Abstract:
A Nisin derivative or variant, comprising an amino acid substitution at amino acid position 29 in the amino acid sequence. The Nisin derivative exhibits enhanced antimicrobial activity when compared to wild type Nisin. The Nisin derivative has an application as a natural food additive and as a therapeutic agent.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the national phase under 35 U.S.C. §371 of International Application No. PCT/EP2010/070597, filed on Dec. 22, 2010, which claims priority to and the benefit of European Patent Application No. 09180498.9 filed on Dec. 22, 2009, the entire disclosures of each of which are incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The present invention relates to lantibiotics and in particular, to the lantibiotic, Nisin. More specifically, the present invention relates to a derivative of Nisin protein that exhibits enhanced bioactivity against a range of microorganisms, compared to the wild type Nisin protein. The present invention further relates to the application of a Nisin derivative as a natural food additive and as a therapeutic agent. 
     BACKGROUND TO THE INVENTION 
     Lantibiotics are gene-encoded, ribosomally synthesized derived peptides that have attracted widespread scientific attention in recent years, not only as promising safe and natural food additives, but also as potential therapeutic agents, such as chemotherapeutic agents. Lantibiotics are produced by a large number of gram-positive bacteria and are considered members of a group of bacterial toxins called bacteriocins. The original and most intensively studied lantibiotic is the Nisin lantibiotic. 
     Nisin is a polycylic, 34 amino acid peptide with antibacterial activity against a range of gram-positive bacteria and a small number of gram-negative bacteria. These include food-borne pathogens, such as staphylococci, bacilli, clostridia and mycobacteria. Nisin A, a natural variant of Nisin, was first marketed in England in 1953 and is FDA approved with a long record of safe use (Delves Broughton, 1990). Nisin A is one of only a few bacteriocins to have been applied commercially (Twomey et al., 2002). To date, six natural variants of Nisin have been identified. These variants are Nisin A (Kaletta and Entian, 1989), Nisin Z (Mulders et al., 1991), Nisin Q (Zendo et al., 2003) and Nisin F (de Kwaadsteniet et al., 2007) which are produced by starter  Lactococcus lactis  species, while Nisin U and Nisin U2 are produced by  Streptococcus uberis  (Wirawan et al., 2006). 
     Studies investigating the mode of action of lanitbiotics have revealed the membrane-bound peptidoglycan precursor lipid II to be the docking molecule for the Nisin lantibiotic. The binding of Nisin to lipid II facilitates two bactericidal activities, namely, membrane pore formation and the inhibition of peptidoglycan biosynthesis (Bonelli et al., 2006; Breukink et al., 1999; Brotz et al., 1998; Wiedemann et al., 2001). The dual activity of Nisin is thought to be due to the presence of two-structural domains located at the N- and C-termini respectively. The N-terminal domain contains three post-translationally incorporated (β-methyl) lanthionine rings (rings A, B, and C) and is linked to the C-terminal rings (rings D and E) by a flexible region, or hinge. It has been established that the A, B and C rings of the N-terminal form a ‘cage’, that facilitates binding to the pyrophosphate moiety of lipid II, thus interfering with the process of cell wall synthesis (Hsu et al., 2004). This binding in turn enhances the ability of the C-terminal segment, containing rings D and E, to form pores in the cell membrane, resulting in the rapid efflux of ions and cytoplasmic solutes, such as amino acids and nucleotides, into the cell (Wiedemann et al., 2001). 
     Nisin&#39;s commercial use in the food industry stems from its ability to suppress gram-positive spoilage and other pathogenic bacteria. It also possesses low anti-gram-negative activity, which increases when combined with other hurdles e.g. high pressure, EDTA chelation, freezing, heating, low pH etc. The use of Nisin is likely to increase in the coming years due to the increased consumer demand for minimally processed foods lacking chemical preservatives. 
     Nisin is also used in the veterinary industry and has been shown to inhibit the gram positive pathogenic bacteria responsible for bovine mastitis including  Streptococcus agalactiae, Strep. dysgalactiae, Strep. uberis  and  Staphylococcus aureus . Bovine mastitis is an inflammation of the udder that is both persistent and costly to treat. Consequently, in recent years Nisin has been incorporated into a number of commercial products that are used as an alternative treatment for bovine mastitis (Sears et al., 1992; Wu et al., 2007). For example, Immucell produce Wipe Out®, used to clean and sanitize the teat area before and after milking. This successfully reduced levels of the mastitis pathogens  Staph. aureus  (99.9%),  Strep. agalactiae  (99.9%),  E. coli  (99%),  Step. uberis  (99%) and  Klebsiella pneumoniae  (99%) in experimental exposure studies (J. Dairy Sci 75:3185-3192). Mast Out®, a Nisin-based treatment for mastitis in lactating cows has been shown to give statistically significant cure rates in an experimental field trial involving 139 cows with subclinical mastitis. Similarly, another lantibiotic, lacticin 3147, has been successfully incorporated into a teat seal product with a view to protecting the seal during the ‘drying-off’ period. 
     Nisin inhibits a number of pathogenic microbes. The effectiveness of Nisin against enterococci and staphylococci and mycobacteria has been shown, as has its activity against  Clostridium difficile.    
     Lantibiotics are generally regarded as possessing poor anti-gram-negative activity. This insensitivity is thought to be due to the inability of the lantibiotic to pass across the outer membrane of the gram-negative cell wall, thus limiting access to lipid II. However, this general trend is not always strictly true. In fact, it has been established that in its purified form, Nisin Z exhibits activity against other gram-negative microbes such as  Escherichia coli  and  S. aureus . Both Nisin A and Z exhibited activity against two antibiotic resistant strains of gram negative  Neisseria gonorrhoeae  and  Helicobacter pylori . Another gram-negative bacteria that has shown susceptibility to Nisin (whether alone or in combination with other antimicrobials) is  Pseudomonas aeruginosa . It should be understood that small amounts of the Nisin peptide may pass through the outer membrane of these targets and, furthermore, this activity can be further enhanced when used in combination with other compounds that disrupt this outer membrane. 
     In yet another application, Nisin has also been shown to have potential as a contraceptive. 
     It has been demonstrated in laboratory settings that bacteria can become resistant to Nisin, e.g. serial exposure of a penicillin-susceptible strain of  Strep. pneumoniae  to Nisin (1 mg/L) in liquid culture resulted in the rapid appearance of stable Nisin-resistant mutants in which the minimum inhibitory concentration (MIC) increased from 0.4 to 6.4 mg/L (Severina, 1998). In these spontaneous mutants, resistance correlates with cell envelope changes such as alterations in membrane charge and fluidity (Li, 2002; Verheul, 1997), cell wall thickness (Maisnier-Patin, 1996), cell wall charge (Mantovani, 2001; Abachin, 2002; Bierbaum, 1987) and combinations thereof (Crandall, 1998), arising following direct exposure to a low level of lantibiotic or as part of an adaptive response to another stress (van Schaik, 1999). The specific mechanism(s) by which cells become resistant to Nisin is not well understood although it is apparent that variations in the lipid II content are not responsible (Kramer, 2004). Genetic loci associated with the development of enhanced Nisin resistance (Cotter, 2002; Gravesen, 2004; Gravesen, 2001) or an innate tolerance of Nisin, have been identified (Peschel, 1999; Abachin, 2002; Cao, 2004). In the latter example, the cell envelope charge would seem to be the most important consideration. While this has not as yet impacted on the application of Nisin in the food industry, it has implications for applications in the future and the potential of Nisin as a clinical antimicrobial. This however, does point to the importance of identifying further antimicrobials, including variants of existing antimicrobials, to overcome resistance problems. 
     The diversity of the Nisin natural variants highlights the ability of certain residues and domains within the molecule to tolerate change. However, comparisons between closely (e.g. subtilin) and more distantly related (e.g. epidermin) lantibiotics revealed that highly conserved elements, with essential structure/function roles, also exist. 
     Despite the relatively plastic nature of the Nisin peptides and of the bioengineered derivatives of Nisin that have been generated and characterized to date, only a limited number (for example, T2S and M17Q/G18T) display increased activity against at least one gram-positive bacteria, and even then, activity is enhanced only with respect to a limited number non-pathogenic indicator strains ( Micrococcus flavus  or  Streptococcus thermophilus ) (Cotter et al., 2005a; Lubelski et al., 2007; Siezen et al., 1996). A recent study by Rink et al, involving the randomization of an N-terminal domain fragment of the Nisin peptide, reported enhanced IC 50 s against specific indicator strains (Rink et al., 2007b). 
     Nisin A is a cationic antimicrobial peptide due to the presence of 5 positively charged residues (Lys12, Lys22, Lys34, His27, His31) and the absence of negatively charged residues. The consequences of charge manipulation to date have been variable. Yuan et al, 2004 disclosed that the incorporation of negatively charged residues had a detrimental impact (e.g. the hinge mutants N20E, M21E and K22E) and subsequently revealed that the introduction of positively charged residues had a more beneficial outcome with respect to anti-gram-negative activity, (N20K and M21K). A further unusual feature of the Nisin lantibiotic is the absence of aromatic residues. To date all aromatic residue-containing forms of Nisin have been bioengineered derivatives and all have displayed reduced antimicrobial activity (i.e. I1W, M17W, V32W, I30W, N20F and N20F/M21L/K22Q (Breukink et al., 1998; Martin et al., 1996; Yuan et al., 2004). Hasper et al, and Wiedemann et al, both established that proline incorporation (i.e. N20P/M21P), resulted in the generation of a Nisin peptide incapable of pore formation. A number of small amino acids have previously been introduced into the hinge region of Nisin Z, including M21G (slightly reduced activity), K22G (slightly reduced activity) and N20A/K22G (as part of an epidermin-like hinge N20A/M21K/Dhb/K22G, greatly reduced activity); (Yuan et al., 2004). It has further been reported by Yuan et al, that an N20Q substitution in Nisin Z results in slightly diminished activity (Yuan et al., 2004). In 2008, Field et al., generated the largest bank of randomly mutated Nisin derivatives reported to date, with the ultimate aim of identifying variants with enhanced bioactivity. This approach led to the identification of a Nisin-producing strain with enhanced bioactivity against the mastitic pathogen  Streptococcus agalactiae  resulting from an amino acid change in the hinge region of the peptide (K22T). Prompted by this discovery, site-directed and site-saturation mutagenesis of the hinge region residues was employed, resulting in the identification of additional derivatives, most notably N20P, M21V and K22S, with enhanced bioactivity and specific activity against Gram-positive pathogens including  Listeria monocytogenes  and/or  Staphylococcus aureus . The identification of these derivatives represents a major step forward in the bioengineering of Nisin and lantibiotics in general. 
     Wirawan et al established that the natural Nisin variants Nisin U and Nisin U2 differ from Nisin A with respect to a number of different amino acids. Chan et al reported that the removal of the C-terminal five residues and a further nine residues, from Nisin to produce Nisin 1-29 or Nisin 1-20, respectively, leads to a 16 fold or 110 fold decrease in bactericidal potency, respectively, compared with that of intact Nisin. Additionally, Sun et al reported that Nisin 1-28 also showed a 100 fold reduced inhibitory activity against  L. lactis  MG1363. 
     Prior to the priority date of the present invention (22 Dec. 2009), no Nisin variants have been reported in which Ser 29 position has been bioengineered. Natural variants such as Nisin U and U2, differ with respect to this location, i.e. contain a natural Ser29His variation, but also contain a number of additional amino acid changes. Thus, the specific significance of the His amino acid change at position 29 is not known. These, and indeed the majority of bioengineered peptides generated to date, have resulted from site-directed approaches, with random bioengineering of the intact Nisin peptide being carried out only on a relatively small scale only. Furthermore, these studies have been largely unsuccessful, yielding derivatives with reduced or absent antimicrobial activity. 
     Published in April 2010, Chinese Patent Application Publication No. CN101691397 documents a Nisin Z mutant variant having S29A change, in which the serine at the 29 position is replaced by alanine. This mutant Nisin Z protein is said to have broader bacteriostatic spectrum for inhibition of gram-positive bacteria such as  Micrococcus flavus, Streptococcus pneumoniae  and  Staphylococcus epidermidis . This Nisin Z mutant is also reported to have a higher stability compared to wild Nisin. 
     The recognition of resistance to lantibiotics such as Nisin is growing, a factor which contributes to the urgent need for alternative antimicrobial peptides that exhibit a superior antimicrobial activity towards gram-positive bacteria. There is thus a need for additional alternative anti-microbial agents, which would be effective against strains that are insensitive to Nisin. The use of Nisin is likely to increase in the coming years due to the increased customer demand for minimally processed foods lacking chemical preservatives. Nisin is also used in the veterinary industry and has potential as a clinical antimicrobial. Despite its general efficacy there exist specific isolates and species of bacteria that are not effectively controlled by Nisin. 
     The invention described herein relates to a set of Nisin derivatives, which possess enhanced antimicrobial activity. Such bioengineered Nisin derivatives demonstrating enhanced activity against specific target strains and producers thereof have a variety of food, veterinary and clinical applications. 
     OBJECT OF THE INVENTION 
     It is an object of the current invention to provide an alternative antimicrobial agent or a producer thereof, with enhanced bioactivity. 
     In particular, it is an object of the current invention to provide an agent or producer thereof, with enhanced bioactivity against gram-positive pathogens and/or gram negative pathogens. 
     In particular, it is an object of the current invention to provide a derivative or variant of the lantibiotic Nisin, displaying enhanced activity against gram-positive and/or gram-negative organisms, particularly against strains of clinical or food relevance. 
     A further object of the current invention is the use of a Nisin derivative in the manufacture of a medicament to treat disease. The disease may be selected from the group consisting of, but not limited to, bovine mastitis, oral infections including dental plaque, gastric ulcers, CDAD ( Clostridum difficile  associated diarrhoea) and acne. 
     It is a still further object of the invention to provide the use of a Nisin derivative as a food additive or a food preservative. 
     It is an additional object of the invention to provide a pharmaceutical composition comprising Nisin derivatives for use in the treatment and prevention of infections caused by gram-positive and/or gram-negative organisms. The pharmaceutical composition can be adapted for use in food/cheese/beverages or it may be formulated with conventional carriers or excipients as oral capsules, intravenously administrable compositions, suppositories, topical creams or ointments or the like 
     SUMMARY OF THE INVENTION 
     In the first aspect of the invention there is provided a mutant of a natural Nisin variant comprising an amino acid substitution resulting in a G, A, E, D, C, M, Q, R, V, P, W, T, N, I, L, H, K, Y or an F amino acid at the 29 position of the amino acid sequence, wherein the Nisin mutant exhibits an antimicrobial activity compared to wild type Nisin, wherein Nisin Z Ser29Ala is excluded. 
     The antimicrobial agent of the invention is a mutant derivative of the lantibiotic Nisin. The mutant of a number of Nisin variants has activity as an antimicrobial agent. By derivative it is meant a mutant of Nisin or a mutant of a natural Nisin variant. 
     The derivative of the Nisin variant may have increased or enhanced antimicrobial activity when compared to wild type Nisin. In other words, a lower concentration of the Nisin derivative is required to inhibit the growth of a microorganism, than the wild type Nisin. Thus, the invention provides a library of Nisin antimicrobial agents or a producer thereof, with enhanced bioactivity. Preferably bioactivity relates to bacteristatic activity which inhibits bacteria function. Most preferably of all, bioactivity refers to bactericidal activity which kills bacteria. 
     Suitably, the derivative of Nisin may be selected from the group of Nisin variants consisting of: Nisin A, Nisin Z, Nisin F and Nisin Q. Preferably, the derivative is of a Nisin variant selected from Nisin A, Nisin F and Nisin Q. More preferably still, the derivative is of a Nisin variant Nisin A. In one embodiment, a preferred derivative is of a Nisin variant Nisin Z. In another embodiment, the derivative is of a Nisin variant Nisin F. In another embodiment still, the derivative is of a Nisin variant Nisin Q. The choice of Nisin variant will typically depend on the desired application and microbes against which activity is desired. 
     The Nisin derivative may comprise at least one amino acid substitution or mutation in the amino acid sequence. Preferably, the amino acid substitution is at amino acid position 29 in the amino acid sequence of a particular variant of the Nisin peptide. Suitably, the 29 position of the variant may comprise any one of an amino acid selected from the group consisting of: G, A, E, D, C, M, Q, R, V, P, W, T, N, I, L, H, K, Y and F. 
     Suitably, the 29 position of the variant may consist of G. Suitably, the 29 position of the variant may consist of A. Suitably, the 29 position of the variant may consist of E. Suitably, the 29 position of the variant may consist of D. Suitably, the 29 position of the variant may consist of C. Suitably, the 29 position of the variant may consist of M. Suitably, the 29 position of the variant may consist of Q. Suitably, the 29 position of the variant may consist of R. Suitably, the 29 position of the variant may consist of V. Suitably, the 29 position of the variant may consist of P. Suitably, the 29 position of the variant may consist of W. Suitably, the 29 position of the variant may consist of T. Suitably, the 29 position of the variant may consist of N. Suitably, the 29 position of the variant may consist of I. Suitably, the 29 position of the variant may consist of L. Suitably, the 29 position of the variant may consist of H. Suitably, the 29 position of the variant may consist of K. Suitably, the 29 position of the variant may consist of Y. Suitably, the 29 position of the variant may consist of F. 
     The substitution at amino acid position 29 may be in any form of Nisin, i.e. Nisin A, U, U2, Z, F or Q. However, the U and U2 variants are less preferred, as they are quite difficult to bioengineer and less relevant structurally in the context of the invention. Therefore in a particularly preferred embodiment, the Nisin variant may be anyone selected from the group of variants comprising Nisin A, Z, F and Q. Suitably, the Nisin variant may be Nisin A. Suitably, the Nisin variant may be Nisin Z. Suitably, the Nisin variant may be Nisin F. Suitably, the Nisin variant may be Nisin Q. In the case where the Nisin variant is Nisin Z, the amino acid substitution at the Serine 29 position may not be Alanine (A). Thus the Nisin Z Ser29Ala mutant per se is excluded, as are vectors, cell lines containing gene encoding for this particular mutant. However, the use of this mutant in bacteriocidal applications is contemplated by the invention. Use of this mutant against gram-negative bacterial and applications involving gram negative bacteria are also comtemplated. 
     The amino acid substitution in the amino acid sequence of any of the Nisin peptide variants may be selected from the substitutions listed in Table 1, Table 1A or Table, shown below. Table 1 also lists the corresponding nucleotide changes, which result in the amino acid mutation at the 29 position. While the table refers to any Nisin variant, the skilled person will appreciate that the nucleotide changes for the given position are identical to those that would be used in any desired variant, with the exception of changes that would result in the Nisin Z Ser29Ala mutant, which is exclude per se from the scope of the invention. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Mutations/substitutions of the Nisin derivatives 
               
               
                 of the current invention (all mutants identified 
               
               
                 and by mass spectroscopy and/or sequence analysis). 
               
             
          
           
               
                 Nisin amino  
                   
               
               
                 acid 
                   
               
               
                 mutation at 
                   
               
               
                 position 29 
                 Nucleotide change(s) 
               
               
                   
               
               
                 Nisin S29G 
                 AGT, AGC to GGT, GGG, GGA, or GGG 
               
               
                 Nisin S29A 
                 AGT, AGC to GCT, GCC, GCA or GCG 
               
               
                 Nisin S29E 
                 AGT, AGC to GAG or GAA 
               
               
                 Nisin S29D 
                 AGT, AGC to GAT or GAC 
               
               
                 Nisin S29C 
                 AGT, AGC to TGT 
               
               
                 Nisin S29M 
                 AGT, AGC to ATG 
               
               
                 Nisin S29Q 
                 AGT, AGC to CAA or CAG 
               
               
                 Nisin S29R 
                 AGT, AGC to CGT, CGC, CGA, CGG, AGA, or 
               
               
                   
                 AGG 
               
               
                 Nisin S29V 
                 AGT, AGC to GTT, GTC, GTA or GTG 
               
               
                 Nisin S29P 
                 AGT, AGC to CCT, CCC, CCA, CCG 
               
               
                 Nisin S29W 
                 AGT, AGC to TGG 
               
               
                 Nisin S29T 
                 AGT, AGC to ACT, ACC, ACA, or ACG 
               
               
                 Nisin S29N 
                 AGT, AGC to AAT or AAC 
               
               
                 Nisin S29I 
                 AGT, AGC to ATT, ATC or ATA 
               
               
                 Nisin S29L 
                 AGT, AGC to CTT, CTC, CTA, CTG, TTA or 
               
               
                   
                 TTG 
               
               
                 Nisin S29H 
                 AGT, AGC to CAC, or CAT 
               
               
                 Nisin S29K 
                 AGT, AGC to AAA, or AAG 
               
               
                 Nisin S29Y 
                 AGT, AGC to TAT, or TAC 
               
               
                 Nisin S29F 
                 AGT, AGC to TTT, or TTC 
               
               
                   
               
               
                 (Ser29 in Nisin A corresponds to the codon AGT; in Nisin F and Nisin Q, the Ser corresponds to AGC; Serine codons corresponding to TCT, TCC, TCA, TCG are proposed) 
               
             
          
         
       
     
     Mutations, other than the above, which also change the nature of the residue are also relevant. A skilled person in the art will appreciate, that alternative nucleotide substitutions yielding equivalent amino acid changes are possible. 
     Suitably, the amino acid substitutions at amino acid position Serine (S) 29 of the Nisin peptide variant may be any amino acid substitution selected from the group consisting of: Glycine (G), Alanine (A), Glutamate (E) or Aspartate (D), Glutamine (Q), Arginine (R), Valine (V), Proline (P), Tryptophan (W), Threonine (T), Asparagine (N), or Isoleucine (I), Leucine (L), Cysteine (C), Methionine (M), Histidine (H), Lysine (K), Tyrosine (Y), Phenylalanine (F) and equivalents thereof. For some variants, these substitutions do not lead to enhanced activity for some strains and so are less preferred. These will be apparent from the description below. 
     Preferably, the amino acid substitutions at amino acid position Serine (S) 29 of the Nisin variant peptide are selected from the group consisting of: Glycine (G), Alanine (A), Glutamate (E), Aspartate (D), Cysteine (C), or Methionine (M) or equivalents thereof. For some variants, these substitutions do not lead to enhanced activity for some strains and so are less preferred, for example Cysteine (C), or Methionine (M) in examples below. These will be apparent from the description below. Thus, in one embodiment, a particularly preferred mutant arises wherein the amino acid substitution results in a Glycine (G), Alanine (A), Aspartate (D), Glutamine (E), Arginine (R), Asparagine (N) or Valine (V) at amino acid position 29 of the amino acid sequence. Most preferred are amino acid substitutions at the Serine 29 position of Arginine (R), Asparagine (N), and Valine (V). For some variants, these substitutions do not lead to enhanced activity for some strains and so are less preferred. These will be apparent from the description below. 
     In one embodiment the preferred amino acid substitution is Glycine (G). 
     In one embodiment the preferred amino acid substitution is Alanine (A) 
     In one embodiment the preferred amino acid substitution is Glutamate (E). 
     In one embodiment the preferred amino acid substitution is Aspartate (D). 
     In one embodiment the preferred amino acid substitution is Glutamine (Q). 
     In one embodiment the preferred amino acid substitution is Arginine (R). 
     In one embodiment the preferred amino acid substitution is Valine (V). 
     In one embodiment the preferred amino acid substitution is Proline (P). 
     In one embodiment the preferred amino acid substitution is Tryptophan (W). 
     In one embodiment the preferred amino acid substitution is Threonine (T). 
     In one embodiment the preferred amino acid substitution is Asparagine (N). 
     In one embodiment the preferred amino acid substitution is Isoleucine (I). 
     In one embodiment the preferred amino acid substitution is Leucine (L). 
     In one embodiment the preferred amino acid substitution is Cysteine (C). 
     In one embodiment the preferred amino acid substitution is Methionine (M). 
     In one embodiment the preferred amino acid substitution is Histidine (H). 
     In one embodiment the preferred amino acid substitution is Lysine (K). 
     In one embodiment the preferred amino acid substitution is Tyrosine (Y). 
     In one embodiment the preferred amino acid substitution is Phenylalanine (F). 
     The mutant Nisin variants as described herein, which comprise an amino acid substitution at amino acid position 29 in the amino acid sequence exhibit an antimicrobial activity compared to wild type Nisin and wherein the antimicrobial activity is against gram-positive bacteria and/or gram-negative bacteria. Thus, the mutant Nisin variants as described herein may be used as an antibacterial. 
     The Nisin derivatives of the current invention display an increased antimicrobial activity against a range of bacterial species compared to the wild type form of the Nisin variant without a mutation or substitution at, at least amino acid position 29. 
     Suitably, the bacterial species are gram-positive organisms. Advantageously, the mutants may be used against gram-negative bacteria. Such enhanced anti gram-negative activity is a surprising find considering to the lack of such activity for the natural strains. Importantly, this anti gram-negative activity is without the need for simultaneous compounds/conditions that disrupt bacterial cell membranes. The skilled person will appreciate that if such cell membrane disruption is initiated, the mutants of the invention will display further activity. 
     It is expected that the mutant Nisin variants as described herein show antimicrobial activity against at least one gram-positive bacteria selected from the group consisting of: lactococci, lactobacilli, carnobacteria, enterococci, streptococci, bacilli, clostridia,  Listeria , staphylococci, propionibacteria,  corynebacteria, eubacterium , mycobacteria and micrococci, with the exception that where the mutant is Nisin Z Ser29Ala, use against  Micrococcus flavus, Streptococcus pneumoniae  and  Staphylococcus epidermidis  is excluded. 
     More specifically, the antimicrobial activity is expected against at least one gram-positive bacteria selected from the group consisting of:  L. lactis, L. monocytogenes, L. innocua, E. faecium, E. faecalis, E. durans, S. aureus, S. epidermidis, S. pyogenes, S. pneumoniae, S. mutans, S. agalactiae, S. dysgalactiae, B. cereus, B. firmus, B. licheniformis, B. stearothermophilus, B. thuringiensis, B. subtilis, C. sporogenes, C. perfringens, C. difficile, P. acnes, M. tuberculosis, M. avium  subsp.  paratuberculosis, M. luteus, M. flavus , with the exception that where the mutant is Nisin Z Ser29Ala, use against  Micrococcus flavus, Streptococcus pneumoniae  and  Staphylococcus epidermidis  is excluded. 
     The inventors have shown that the mutant Nisin variants show enhanced activities against gram-positive bacteria selected from the group consisting of:  L. monocytogenes , MRSA,  S. aureus, C. difficile, L. lactis, C. sporogenes, B. cereus, Strep. galactiae , VISA,  S. epidermidis, S. hominis, Bacillus firmus, Strep. dysgalactiae, Strep. mutans , VRE,  Enterococcus durans, Propionibacterium acnes  and  Micrococcus luteus , with the exception that where the mutant is Nisin Z Ser29Ala, use against  Staphylococcus epidermidis  is excluded. 
     It is expected that the mutant Nisin variants as described herein show antimicrobial activity against at gram-negative bacteria selected from the group consisting of:  C. sakazakii, Escherichia coli, Shigella flexneri, Salmonella enteritidis, Pseudomonas aeruginosa, Campylobacter jejuni, Campylobacter coli, Hemophilus influenzae, Klebsiella pneumoniae, Legionella pneumophila, Proteus mirabilis, Enterobacter cloacae, Serratia marcescens, Helicobacter pylori, Salmonella typhi, Acinetobacter baumannii, Yersinia enterocolitica, Aeromonas hydrophila, Bacteroides fragilis, Bacteroides  spp.,  Prevotella  spp.,  Porphyromonas  spp. and  Fusobacterium  spp. 
     More specifically, the antimicrobial activity is expected against gram-negative organisms selected from the group consisting of:  Escherichia coli, Salmonella enteritidis, Pseudomonas aeruginosa, Campylobacter jejuni, Campylobacter coli, Hemophilus influenzae, Klebsiella pneumoniae, Legionella pneumophila, Proteus mirabilis, Enterobacter cloacae, Serratia marcescens, Helicobacter pylori, Salmonella typhi, Acinetobacter baumannii  and  Cronobacter sakazakii.    
     In particular, gram-negative organisms are preferably  Cronobacter sakazakii.    
     For some mutant variants, these substitutions do not lead to enhanced activity for some strains and so are less preferred. These will be apparent from the description below. 
     In particular, the following uses are preferred: 
     Nisin A S29G, S29A, S29R mutants against  L. monocytogenes,    
     Nisin A S29G, S29A, S29D, S29E, Nisin Z S29G, NisinQ S29A against  S. aureus,    
     Nisin A S29G, S29A, S29D against MRSA, 
     Nisin A S29G, S29A, S29E against VISA, 
     Nisin A S29G, Nisin A S29A against  S. epidermidis,    
     Nisin A S29G, Nisin A S29A, Nisin A S29D against  S. hominis,    
     Nisin A S29G, S29A, S29D, S29E, Nisin Z S29G, S29D, S29E, S29N, Nisin F S29A, S29E, S29V, S29N, Nisin Q S29A, S29D, S29E, S29P against  L. lactis,    
     Nisin A S29G, S29A against  B. cereus,    
     Nisin A S29A, S29D against  Bacillus firmus,    
     Nisin A S29G, Nisin A S29A, Nisin A S29D against  Strep. agalactiae,    
     Nisin A S29G, Nisin A S29A, Nisin A S29D, Nisin A S29E against  Strep. dysgalactiae,    
     Nisin A S29G, Nisin A S29A, Nisin A S29D, Nisin A S29E against  Strep. mutans,    
     Nisin A S29G, Nisin A S29D, Nisin A S29E against VRE, 
     Nisin A S29G, Nisin A S29A, Nisin A S29D, Nisin A S29E against  Enterococcus durans,    
     Nisin A S29G, Nisin A S29D, Nisin A S29E against  Propionibacterium acnes , and 
     Nisin A S29G, Nisin A S29D against  Micrococcus luteus.    
     Suitably, the amino acid substitution at position Serine (5) 29 may be Glycine (G), wherein the Nisin variant is Nisin A. This Nisin A S29G mutant is particularly useful against  L. monocyotgenes, L. lactis, S. aureus, S. hominis, S. epidermidis, S. agalactiae, S. dysgalactiae, S. mutans , Vancomycin resistant  Enterococcus, E. faecium  and  E. durans  5133 , P. acnes, B. cereus, M luteus  and  C. sakazakii.    
     Suitably, the amino acid substitution at position Serine (5) 29 may be Alanine (A), wherein the Nisin variant is Nisin A. This Nisin A S29A mutant is particularly useful against  L. lactis, S. aureus, S. hominis, S. epidermidis, S. mutans, S. agalactiae, Enterococcus durans, Enterococcus faecium, Bacillus cereus, Bacillus firmus, Enterococcus durans, L. monocytogenes  LO28 and  C. sakazakii    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Aspartate (D), wherein the Nisin variant is Nisin A. This Nisin A S29D mutant is particularly useful against  L. lactis, S. aureus, S. hominis  IMF12 , S. agalactiae, S. mutans, S. dysgalactiae  43078, Vancomycin resistant  Enterococcus, E. faecium, E. durans, P. acnes, B. firmus, M. luteus  and  C. sakazakii.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Glutamate (E), wherein the Nisin variant is Nisin A. This Nisin A S29E mutant is particularly useful against  L. lactis, S. aureus, S. dysgalactiae, S. mutans , Vancomycin resistant  Enterococcus, E. durans, P. acnes  and  C. sakazakii.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Glycine (G), wherein the Nisin variant is Nisin Z. This Nisin Z S29G mutant is particularly useful against  S. aureus  and  L. lactis.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Aspartate (D), wherein the Nisin variant is Nisin Z. This Nisin Z S29D mutant is particularly useful against  L. lactis.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Glutamate (E), wherein the Nisin variant is Nisin Z. This Nisin Z S29E mutant is particularly useful against  L. lactis.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Alanine (A), wherein the Nisin variant is Nisin F. This Nisin F S29A mutant is particularly useful against  L. lactis.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Glutamate (E), wherein the Nisin variant is Nisin F. This Nisin F S29E mutant is particularly useful against  L. lactis.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Alanine (A), wherein the Nisin variant is Nisin Q. This Nisin Q S29A mutant is particularly useful against  L. lactis  and  S. aureus.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Aspartate (D), wherein the Nisin variant is Nisin Q. This Nisin Q S29D mutant is particularly useful against  L. lactis.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Glutamate (E), wherein the Nisin variant is Nisin Q. This Nisin Q S29E mutant is particularly useful against  L. lactis.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Arginine (R), wherein the Nisin variant is Nisin A. This Nisin A S29R mutant is particularly useful against  Listeria monocytogenes  and  Cronobacter sakazakii.    
     Suitably, the amino acid substitution at position Serine (S) 29 may be Asparagine (N), wherein the Nisin variant is Nisin Z and/or Nisin F. The Nisin Z S29N mutant is particularly useful against  L. lactis  HP. The Nisin F S29N mutant is particularly useful against  L. lactis  HP. 
     Suitably, the amino acid substitution at position Serine (S) 29 may be Valine (V), wherein the Nisin variant is Nisin F. The Nisin F S29V mutant is particularly useful  L. lactis  HP. 
     Suitably, the amino acid substitution at position Serine (S) 29 may be Proline (P), wherein the Nisin variant is Nisin Q. The Nisin F S29P mutant is particularly useful  L. lactis  HP. 
     In the case where the variant is the Nisin Z variant, mutation at the 29 position cannot be Alanine (A). 
     The skilled person will appreciate that the advantages arising from Nisin variants having Serine-29 mutations may still arise where other substitutions are made to the Nisin variant amino acid sequence. In other words, included within the scope of the invention are all Nisin Serine-29 mutants with at least one further amino acid sequence substitutions wherein the advantageous activity is retained. 
     In a related aspect, the Nisin variant mutants may comprise at least one further amino acid substitution at amino acid position 30 in the amino acid sequence. Thus, the Nisin variant may be derivatized to comprise two mutations or more mutations in the peptide chain. Suitably, for example, a double mutants arises wherein the amino acids at the 29 and 30 positions are altered simultaneously. Suitably, double mutants arises wherein the amino acid substitution results in a Glycine (G), Alanine (A), Aspartate (D), Glutamine (E), Arginine (R), Asparagine (N) or Valine (V) at amino acid position 29 of the amino acid sequence and wherein the further amino acid substitution results in a Valine (V), Leucine (L), Isoleucine (I), Alanine (A), Glycine (G) at amino acid position 30 of the amino acid sequence. Most preferably, the double mutants comprise an A, D, E or N at the 29 position. Suitably, the 30 position comprises a V, L, I, A, or G substitution. 
     Any combinations of these substitutions are contemplated and are expected to show antimicrobial activity. Particularly preferred double mutants are shown below in Table 1A, as are their activities against the bacteria indicated. 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 
                   L. lactis 
                 
                 
                   S. aureus 
                 
                 
                   L. mono 
                 
               
               
                 Serine29X 
                 Isoleucine30X 
                 HP 
                 RF122 
                 LO28 
               
               
                   
               
             
             
               
                 D 
                 V 
                 ✓ 
                   
                   
               
               
                 D 
                 L 
                 ✓ 
                   
                   
               
               
                 D 
                 I 
                 ✓ 
                 ✓ 
                 ✓ 
               
               
                 A 
                 V 
                   
                 ✓ 
                   
               
               
                 E 
                 L 
                 ✓ 
                 ✓ 
                 ✓ 
               
               
                 E 
                 A 
                 ✓ 
                   
                   
               
               
                 S 
                 G 
                 ✓ 
                   
                   
               
               
                 S 
                 V 
                 ✓ 
                 ✓ 
                 ✓ 
               
               
                 N 
                 L 
                 ✓ 
               
               
                   
               
             
          
         
       
     
     Suitably, the gram-positive organisms are selected from the group consisting of bacilli, clostridia, mycobacteria,  S. aureus  including met(h)icillin resistant (MRSA), vancomycin insensitive (VISA) and heterogeneous vancomycin insensitive (hVISA) forms,  Listeria , enterococci including vancomycin resistant (VRE) forms, lactobacilli, lactococci, propionibacteria, micrococci and streptococci. In another embodiment, gram-positive organisms clostridia is expected to be susceptible. The gram positive bacteria may be selected from the group consisting of:  L. monocyotgenes  10403s,  L. monocyotgenes  EGDe ΔvirR,  L. monocytogenes  EGDe Δmprf,  L. monocytogenes  LO28 , Lactococcus lactis  MG1363 , L. lactis  HP,  S. hominis  IMF12 , Staphylococcus aureus  SA113 , S. aureus  DPC 5247 , S. aureus  NCD1499 , S. aureus  RF122 , S. aureus  Newman,  S. aureus  528 (MRSA),  S. aureus  530 (MRSA),  S. aureus  523 (MRSA),  S. epidermidis  IMF54, hVISA32652, hVISA32679 , Streptococcus agalactiae  ATCC13813 , Streptococcus dysgalactiae  43078, and  Streptococcus mutans , Vancomycin resistant  Enterococcus  VRE Ec520, VRE Ec295, VRE Ec533, VRE Ec725, VRE Ec538 , Enterococcus faecium  IMF91 , Enterococcus durans  5133 , Enterococcus durans  IMF90 , Propionibacterium acnes, Bacillus cereus  IMF4 , Micrococcus luteus. Bacillus cereus  DPC 6088 and  Bacillus firmus  IMF68. 
     Suitably, the gram negative bacteria may be selected from the group consisting of  C. sakazakii  DPC 6440 , C. sakazakii  DPC 6441 , C. sakazakii  DPC 6442 , C. sakazakii  DPC 6443 , C. sakazakii  DPC 6444 , C. sakazakii  DPC 6448 , C. sakazakii  DPC 6522 , C. sakazakii  DPC 6524 , C. sakazakii  DPC6440 , C. sakazakii  DPC6442 and  C. sakazakii  DPC6446. 
     Table 2 lists a number of Nisin variant mutant derivatives of Nisin A, Z, F and Q of the current invention, all of which contain substitutions at amino acid position 29 of the Nisin peptide. Enhanced bioactivity against the strains listed is observed when compared to wild type Nisin with no amino acid substitution at amino acid position 29 (i.e. deferred antagonism agar-based overlay assays) against the strains listed. The Nisin Z Ser29Ala mutant per se is excluded. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Nisin derivatives with enhanced bioactivity 
               
             
          
           
               
                   
                 Strain 
               
               
                   
               
               
                 Nisin A 
                   
               
               
                 Derivative 
                   
               
               
                 Nisin 
                 Gram Positive:  L. monocyotgenes  10403s,  L. monocyotgenes   
               
               
                 S29G 
                 EGDe ΔvirR and  L. monocytogenes  EGDe Δmprf,  Lactococcus   
               
               
                   
                   lactis  MG1363,  L. lactis  HP,  S. hominis  IMF12, 
               
               
                   
                   Staphylococcus aureus  SA113,  S. aureus  DPC 5247,  S. aureus   
               
               
                   
                 NCD1499,  S. aureus  RF122,  S. aureus  Newman,  S. aureus  528 
               
               
                   
                 (MRSA),  S. aureus  530 (MRSA),  S. aureus  523 (MRSA),  S.   
               
               
                   
                   epidermidis  IMF54, hVISA32652, hVISA32679,  Streptococcus   
               
               
                   
                   agalactiae  ATCC13813,  Streptococcus dysgalactiae  43078, 
               
               
                   
                 and  Streptococcus mutans , Vancomycin resistant  Enterococcus   
               
               
                   
                 VRE Ec520, VRE Ec295, VRE Ec533, VRE Ec725, VRE 
               
               
                   
                 Ec538,  Enterococcus faecium  IMF91,  Enterococcus durans   
               
               
                   
                 5133,  Enterococcus durans  IMF90,  Propionibacterium acnes , 
               
               
                   
                   Bacillus cereus  IMF4 and  Micrococcus luteus . 
               
               
                   
                 Gram Negative:  C. sakazakii  DPC 6440,  C. sakazakii  DPC 
               
               
                   
                 6441,  C. sakazakii  DPC 6442,  C. sakazakii  DPC 6443,  C.   
               
               
                   
                   sakazakii  DPC 6444,  C. sakazakii  DPC 6448,  C. sakazakii   
               
               
                   
                 DPC 6522,  C. sakazakii  DPC 6524,  C. sakazakii  DPC6440,  C.   
               
               
                   
                   sakazakii  DPC6442,  C. sakazakii  DPC6446. 
               
               
                 S29A 
                 Gram Positive:  L. lactis  MG1363,  L. lactis  HP,  S. aureus   
               
               
                   
                 SA113,  S. aureus  DPC 5247,  S. aureus  NCD01499,  S. aureus   
               
               
                   
                 RF122,  S. hominis  IMF12,  S. epidermidis  IMF54,  S. mutans ,  S.   
               
               
                   
                   agalactiae  ATCC13813,  S. aureus  528 (MRSA),  S. aureus  530 
               
               
                   
                 (MRSA), hVISA32652, hVISA32679,  Enterococcus durans   
               
               
                   
                 5133,  Bacillus cereus  DPC 6088,  Bacillus cereus  IMF4, 
               
               
                   
                   Bacillus firmus  IMF68,  Enterococcus faecium  IMF91, 
               
               
                   
                   Enterococcus durans  IMF90,  L. monocytogenes  LO28 and  L.   
               
               
                   
                   monocyotgenes  10403s. 
               
               
                   
                 Gram Negative:  C. sakazakii  DPC 6440,  C. sakazakii  DPC 
               
               
                   
                 6441,  C. sakazakii  DPC 6442,  C. sakazakii  DPC 6443,  C.   
               
               
                   
                   sakazakii  DPC 6444,  C. sakazakii  DPC 6522,  C. sakazakii   
               
               
                   
                 DPC 6524,  C. sakazakii  DPC6440,  C. sakazakii  DPC6442, 
               
               
                   
                   C. sakazakii  DPC6446 
               
               
                 S29D 
                 Gram Positive:  L. lactis  HP,  S. aureus  DPC 5247,  S. aureus   
               
               
                   
                 NCD01499,  S. hominis  IMF12,  S. agalactiae  ATCC13813, 
               
               
                   
                   Streptococcus mutans ,  Streptococcus dysgalactiae  43078,  S.   
               
               
                   
                   aureus  Newman,  S. aureus  528 (MRSA),  S. aureus  523 
               
               
                   
                 (MRSA), VRE Ec295, VRE Ec725, VRE Ec538,  Lactococcus   
               
               
                   
                   lactis  MG1363,  L. lactis  HP,  Propionibacterium acnes , 
               
               
                   
                   Bacillus firmus  IMF68,  Enterococcus faecium  IMF91, 
               
               
                   
                   Enterococcus durans  IMF90, and  Micrococcus luteus . 
               
               
                   
                 Gram Negative:  C. sakazakii  DPC6446. 
               
               
                 S29E 
                 Gram Positive:  L. lactis  HP,  S. aureus  DPC 5247,  S. aureus   
               
               
                   
                 NCD01499,  Streptococcus dysgalactiae  43078,  S. mutans ,  S.   
               
               
                   
                   aureus  Newman, hVISA32652 Ec295, VRE Ec533  L. lactis   
               
               
                   
                 HP,  Enterococcus durans  5133,  Enterococcus durans  IMF90, 
               
               
                   
                 and  Propionibacterium acnes . 
               
               
                   
                 Gram Negative:  C. sakazakii  DPC 6442,  C. sakazakii  DPC 
               
               
                   
                 6443,  C. sakazakii  DPC 6448,  C. sakazakii  DPC6446. 
               
               
                 S29R 
                 Gram Positive:  Listeria monocytogenes  LO28, 
               
               
                   
                 Gram Negative:  C. sakazakii  DPC6446. 
               
               
                 Nisin Z 
                   
               
               
                 Derivative 
                   
               
               
                 S29G 
                   S. aureus  RF122,  L. lactis  HP 
               
               
                 S29D 
                   L. lactis  HP 
               
               
                 S29E 
                   L. lactis  HP 
               
               
                 S29N 
                   L. lactis  HP 
               
               
                 Nisin F 
                   
               
               
                 Derivative 
                   
               
               
                 S29A 
                   L. lactis  HP 
               
               
                 S29E 
                   L. lactis  HP 
               
               
                 S29V 
                   L. lactis  HP 
               
               
                 S29N 
                   L. lactis  HP 
               
               
                 Nisin Q 
                   
               
               
                 Derivative 
                   
               
               
                 S29A 
                   L. lactis  HP,  S. aureus  RF122 
               
               
                 S29D 
                   L. lactis  HP 
               
               
                 S29E 
                   L. lactis  HP 
               
               
                 S29P 
                   L. lactis  HP 
               
               
                   
               
             
          
         
       
     
     Advantageously, Nisin A S29G has been found to be more active against  Listeria monocytogenes  L028 , L. monocytogenes  10403s,  L. monocytogenes  EGDe ΔvirR and  L. monocytogenes  EGDe Δmprf  Lactococcus lactis  MG1363 , L. lactis  HP,  Bacillus cereus, Staphylococcus aureus  SA113 , S. aureus  DPC 5247 , S. aureus  NCD1499 , S. aureus  RF122 , S. aureus  Newman,  S. aureus  528 (MRSA),  S. aureus  530 (MRSA),  S. aureus  523 (MRSA),  S. epidermidis  IMF54, hVISA32652, hVISA32679 , S. hominis  IMF12 , Streptococcus agalactiae ATCC 13813 , Streptococcus dysgalactiae  43078 , Streptococcus mutans , Vancomycin resistant  Enterococcus  VRE Ec520, VRE Ec295, VRE Ec533, VRE Ec725, VRE Ec538 , E. faecium  IMF91 , Enterococcus durans  5133 , Enterococcus durans  IMF90 , Bacillus cereus  IMF4 , Propionibacterium acnes, Micrococcus luteus, Cronobacter sakazakii  DPC 6440 , C. sakazakii  DPC 6441 , C. sakazakii  DPC 6442 , C. sakazakii  DPC 6443 , C. sakazakii  DPC 6444 , C. sakazakii  DPC 6448 , C. sakazakii  DPC 6522 , C. sakazakii  DPC 6524 , C. sakazakii  DPC6440 , C. sakazakii  DPC6442 , C. sakazakii  DPC6446 than natural Nisin A. 
     Nisin A S29A is more active against  L. lactis  MG1363 , L. lactis  HP,  S. aureus  SA113 , S. aureus  DPC 5247 , S. aureus  NCD01499 , S. aureus  RF122 , S. hominis  IMF12 , S. epidermidis  IMF54 , S. mutans, S. agalactiae  ATCC13813 , S. aureus  528 (MRSA),  S. aureus  530 (MRSA), hVISA32652, hVISA32679 , Enterococcus durans  5133 , Bacillus cereus  DPC 6088 , Bacillus cereus  IMF4 , Bacillus firmus  IMF68 , Enterococcus faecium  IMF91 , Enterococcus durans  IMF90 , L. monocytogenes  LO28 , L. monocyotgenes  10403s,  C. sakazakii  DPC 6440 , C. sakazakii  DPC 6441 , C. sakazakii  DPC 6442 , C. sakazakii  DPC 6443 , C. sakazakii DPC  6444 , C. sakazakii  DPC 6522 , C. sakazakii  DPC 6524 , C. sakazakii  DPC6440 , C. sakazakii  DPC6442 , C. sakazakii  DPC6446 than natural Nisin A. 
     Nisin A S29D is more active against  L. lactis  HP,  S. aureus  DPC 5247 , S. aureus  NCD01499 , S. agalactiae  ATCC13813 , Streptococcus mutans, Streptococcus dysgalactiae  43078 , S. aureus  Newman,  S. aureus  528 (MRSA),  S. aureus  523 (MRSA),  S. hominis  IMF12, VRE Ec295, VRE Ec725, VRE Ec538  Lactococcus lactis  MG1363 , L. lactis  HP,  Propionibacterium acnes, Bacillus cereus, Bacillus firmus  IMF68 , Enterococcus faecium  IMF91 , Enterococcus durans  IMF90 , Micrococcus luteus, C. sakazakii  DPC6446 than natural Nisin A. 
     Nisin A S29E is more active against  L. lactis  HP,  S. aureus  DPC 5247 , S. aureus  NCD01499 , Streptococcus  dysgalactiae 43078 , S. mutans, S. aureus  Newman, hVISA32652, Ec295, VRE Ec533 , Enterococcus durans  5133 , Enterococcus durans  IMF90 , Propionibacterium acnes, C. sakazakii  DPC 6442 , C. sakazakii  DPC 6443 , C. sakazakii  DPC 6448 , C. sakazakii  DPC6446 than natural Nisin A. 
     Nisin A S29R is more active against  L. monocytogenes  LO28 and  C. sakazakii  DPC6440 than natural Nisin A. 
     Nisin Z S29G is more active against  S. aureus  RF122 and  L. lactis  HP than natural Nisin Z. 
     Nisin Z S29G is more active against  L. lactis  HP than natural Nisin Z. 
     Nisin Z S29D is more active against  L. lactis  HP than natural Nisin Z. 
     Nisin Z S29E is more active against  L. lactis  HP than natural Nisin Z. 
     Nisin Z S29N is more active against  L. lactis  HP than natural Nisin Z. 
     Nisin F S29A is more active against  L. lactis  HP than natural Nisin F. 
     Nisin F S29E is more active against  L. lactis  HP than natural Nisin F. 
     Nisin F S29V is more active against  L. lactis  HP than natural Nisin F. 
     Nisin F S29N is more active against  L. lactis  HP than natural Nisin F. 
     Nisin Q S29A is more active against  L. lactis  HP and  S. aureus  RF122 than natural Nisin Q. 
     Nisin Q S29D is more active against  L. lactis  HP than natural Nisin Q. 
     Nisin Q S29E is more active against  L. lactis  HP than natural Nisin Q. 
     Nisin Q S29P is more active against  L. lactis  HP than natural Nisin Q. 
     Use of the nisin Z Ser29Ala mutant against gram positive bacteria such as  Micrococcus flavus, Streptococcus pneumoniae  and  Staphylococcus epidermidis  is excluded from the scope of the present invention. This is particularly the case where bacteriostatic activity is desired. However, the Nisin Z Ser29Ala mutant may be advantageously used against gram-negative bacteria. Suitably, such gram-negative bacteria include:  Escherichia coli, Salmonella enteritidis, Pseudomonas aeruginosa, Campylobacter jejuni, Campylobacter coli, Hemophilus influenzae, Klebsiella pneumoniae, Legionella pneumophila, Proteus mirabilis, Enterobacter cloacae, Serratia marcescens, Helicobacter pylori, Salmonella typhi, Acinetobacter baumannii  and  Cronobacter sakazakii.    
     In particular, Nisin Z Ser29Ala mutant may be used against gram-negative organisms are preferably  Cronobacter sakazakii.    
     Suitably, Nisin Z Ser29Ala mutant may be used against the gram negative bacteria may be selected from the group consisting of  C. sakazakii  DPC 6440 , C. sakazakii  DPC 6441 , C. sakazakii  DPC 6442 , C. sakazakii  DPC 6443 , C. sakazakii  DPC 6444 , C. sakazakii  DPC 6448 , C. sakazakii  DPC 6522 , C. sakazakii  DPC 6524 , C. sakazakii  DPC6440 , C. sakazakii  DPC6442 and  C. sakazakii  DPC6446. 
     In a further aspect of the current invention, there is provided the use of a mutant derivative of Nisin or a Nisin variant, as a food or beverage additive, preservative or shelf life extender (the skilled person will appreciate that this is intended to mean that the mutation is found in any natural Nisin variant). Such additives may be in liquid form and/or tablet form. The derivatives of the invention may be incorporated directly, as part of an ingredient or via in situ production by a microorganisms, into liquids (including milk or beer), foods or related packaging either alone or in combination with of a large variety of other agents (or combined with high temp, high pressure, etc.). 
     In a further embodiment, there is provided a food additive comprising a mutant derivative of Nisin or a Nisin variant, as described herein. 
     According to a further embodiment of the invention still, there is provided for use of a mutant derivative of Nisin or a Nisin variant in the manufacture of a medicament for the treatment or prevention of disease caused by gram-positive and/or gram-negative pathogens. 
     Furthermore, the invention contemplates the use of a mutant Nisin or mutant Nisin variant producing strain for the treatment or prevention of disease. 
     Suitably, the disease may include, but is not limited to, bovine mastitis, oral infections including dental plaque and bad breath, gastric ulcers, CDAD ( Clostridum difficile  associated diarrhoea), acne, and bacterial infections generally. 
     The bacterial infections may be caused by gram-positive and/or gram-negative bacteria. 
     The mutant derivative of Nisin or a Nisin variant as described herein may also find use as spermicides, surfactants or preservatives. 
     For example, suitably, the Nisin derivatives of the current invention may be used as a preservative in cosmetics or in eye drops. 
     A further aspect of the current invention provides a pharmaceutical composition for use in the treatment and prevention of infections caused by gram-positive organisms and/or gram-negative organisms, wherein said composition comprises a mutant derivative of Nisin or a Nisin variant derivative of the invention. The pharmaceutical composition, comprising the mutant of any one of may be together with a pharmaceutically acceptable carrier or excipient. 
     A preferred embodiment of the current invention provides for a pharmaceutical composition for use in the treatment and prevention of infections caused by gram-negative organisms, wherein the composition comprises a Nisin derivative of the invention. 
     The pharmaceutical composition may include a carrier or excipient as appropriate. 
     The present invention also provides use of the Nisin and Nisin variant derivatives of the current invention (which have enhanced bioactivity), as a pharmaceutical composition, a disinfectant, or a food additive, together with carriers or excipients, as appropriate. 
     A particularly preferred use of the mutants of the invention are as food additives. 
     Other preferred uses include use of a natural Nisin variant comprising an amino acid substitution at amino acid position 29 in the amino acid sequence; or use of a mutant of a natural Nisin variant comprising an amino acid substitution at amino acid position 29 comprising at least one further amino acid substitution, preferably at the amino acid position 30 in the amino acid sequence, or use of mixtures thereof, wherein the Nisin derivative exhibits an antimicrobial activity compared to wild type Nisin, in cheese pasteurisation, as a compound to extend: shelf-life, increase safety and quality of food products in beverage production, in cosmetic preservation, as a spermicide, as a surfactant or as a disinfectant. 
     According to another embodiment of the present invention, there is provided a vector/plasmid comprising a sequence encoding a Nisin derivative as defined above. Suitably, the sequence may be an amino acid sequence or a nucleotide sequence. 
     The present invention further provides a host cell, for example, a bacterium host cell, with a vector encoding a Nisin derivative of the present invention. In a related aspect, the present invention also relates to a Nisin derivative or a host producing a Nisin derivative of the current invention. 
     In another aspect, the invention also provides a method of treating or preventing a disease comprising a Nisin derivative of the current invention, as described herein. 
     Suitably, the disease may be caused by gram-positive or negative pathogens, or mixtures of both. The disease may be selected from the group consisting of: bovine mastitis, dental plaque, gastric ulcers, CDAD ( Clostridum difficile  associated diarrhoea), acne and bacterial infections. 
     Table 3 provides the molecular weights of the Nisin A S29 derivatives as observed by mass spectrometry are listed. In the case of S29C, colony mass spec did not yield a detectable mass. This mutant was identified by sequence analysis of colonies producing little/no detectable zone of inhibition (Sep. 9, 2009). The molecular weights of some derivatives of the invention are as follows:— 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 S29X derivatives identified in NisinA, 
               
               
                 NisinZ, NisinF and NisinQ backgrounds. 
               
             
          
           
               
                 Amino 
                   
                   
                   
                   
               
               
                 acid 
                 NisinA-S29X 
                 NisinZ-S29X 
                 NisinF-S29X 
                 NisinQ-S29X 
               
               
                   
               
               
                 N 
                 3379.66 
                 3358.92 
                 3341.45 
                 nd 
               
               
                 Q 
                 3393.69 
                 3372.41 
                 nd 
                 3367.38 
               
               
                 C 
                 3368.70 
                 nd 
                 nd 
                 nd 
               
               
                 G 
                 3322.60 
                 3300.64 
                 3286.77 
                 3299.07 
               
               
                 A 
                 3336.64 
                 3314.55 
                 3299.41 
                 3311.85 
               
               
                 S 
                 3353.15 
                 3331.63 
                 3316.85 
                 3327.50 
               
               
                   
                 (WT) 
                 (WT) 
                 (WT) 
                 (WT) 
               
               
                 T 
                 3366.66 
                 3344.91 
                 3329.03 
                 3342.64 
               
               
                 V 
                 3364.69 
                 3343.08 
                 3327.44 
                 3340.10 
               
               
                 L 
                 3378.71 
                 3356.42 
                 3341.95 
                 3353.85 
               
               
                 I 
                 3378.71 
                 3356.06 
                 3340.50 
                 3353.85 
               
               
                 P 
                 3362.67 
                 3341.27 
                 3326.56 
                 3338.64 
               
               
                 M 
                 3396.74 
                 3374.82 
                 3360.86 
                 nd 
               
               
                 F 
                 3412.73 
                 3390.79 
                 3376.40 
                 nd 
               
               
                 Y 
                 3428.73 
                 3407.16 
                 3394.39 
                 3403.74 
               
               
                 W 
                 3451.76 
                 3429.48 
                 3415.04 
                 nd 
               
               
                 D 
                 3380.64 
                 3355.30 
                 3343.60 
                 3354.11 
               
               
                 E 
                 3394.67 
                 3373.15 
                 3357.93 
                 3367.97 
               
               
                 R 
                 3421.74 
                 3399.69 
                 3385.13 
                 3397.29 
               
               
                 H 
                 3402.69 
                 nd 
                 3364.28 
                 3376.93 
               
               
                 K 
                 3393.72 
                 3372.66 
                 nd 
                 nd 
               
               
                   
               
               
                 nd—derivative not detected 
               
             
          
         
       
     
     In a related aspect, the invention further provides primers or probes to detect or amplify the substitutions or a Nisin derivative of the current invention. 
     The terms “Nisin Derivative” or “Nisin Variant” as used herein refer to a Nisin peptide or protein or natural variant thereof, with at least one amino acid mutation or substitution in the amino acid sequence. 
     The term “wild type Nisin” refers to a Nisin peptide or protein without an amino acid substitution or mutation at amino acid position 29. 
     Unless otherwise defined, all terms of scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art. In some cases, terms are defined herein for clarity and should not be intended to limit the scope of the invention in any way. It is to be understood that the following detailed description and accompanying figures, are exemplary and explanatory only and are intended to provide a further explanation of the present invention, as claimed and not to limit the scope of the invention in any way. 
     The current invention will now be described with reference to the following examples. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates a photograph of the results of an Agar-based deferred antagonism assay (spot on lawn) of Nisin A S29 derivatives (left) and agarose-based antagonism assays (supernatants) (right) against the indicator strain  Lactococcus lactis  HP; 
         FIG. 2  illustrate a growth curve analysis of purified Nisin A and Nisin A S29G and S29A derivatives against  C. sakazakii  DPC6440 (1×10 5  initial inoculum) at 100 μg/ml final concentration and of the same peptides, as well as Nisin A S29R, at a 30 μM concentration against the same target. 
         FIG. 3  illustrates a photo of the deferred antagonism assays of Nisin A-S29X variants against  L. lactis  HP. 
         FIG. 4  illustrates the results of deferred antagonism assays of Nisin Z-S29X variants against  S. aureus  RF122 and  L. lactis  HP; 
         FIG. 5  illustrate the results of deferred antagonism assays of Nisin F-S29X variants against  L. lactis  HP; 
         FIG. 6  illustrate the results of deferred antagonism assays of Nisin Q-S29X variants against  L. lactis  HP; 
         FIG. 7  illustrates the results of deferred antagonism assays of select Nisin A-S29XX variants against  L. lactis  HP and  S. aureus  RF122. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Materials and Methods 
     Bacterial Strains and Growth Conditions 
     Bacterial strains and plasmids used in this study are listed in Table 4 . L. lactis  strains were grown in M17 broth supplemented with 0.5% glucose (GM17) or GM17 agar at 30° C.  E. coli  was grown in Luria-Bertani broth with vigorous shaking or agar at 37° C.  S. aureus  and  Micrococcus luteus  strains were grown in Mueller-Hinton (MH) broth (Oxoid) or MH agar at 37° C., streptococci and  Bacillus  strains were grown in Tryptic soy broth (TSB) or TSB agar at 37° C.,  Listeria  strains were grown in Brain Heart Infusion (BHI) or BHI agar at 37° C. Vancomycin resistant enterococci (VRE) were cultured in cation-adjusted Mueller-Hinton broth in accordance with the CLSI microbroth method at 37° C. without aeration. Antibiotics were used where indicated at the following concentrations: Chloramphenicol at 10 and 20 μg ml −1 , respectively for  L. lactis  and  E. coli . Tetracycline was used at 10 μg ml −1  for  L. lactis  and  E. coli  and ampicillin was used at 50 μg ml for  E. coli . 
                                   TABLE 4                   Bacterial strains and plasmids utilised in the current study.            Strain/plasmids   Relevant characteristics   Reference               Strains                 L. lactis  NZ9700   Wild type Nisin producer   (Kuipers et al. 1993;               Kuipers et al. 1998)         L. lactis  NZ9800     L. lactis  NZ9700 ΔnisA   (Kuipers et al. 1993;               Kuipers et al. 1998)         L. lactis  NZ9800     L. lactis  NZ9800    (Field et al., 2008)       pPTPL   harbouring             L. lactis  NZ9800   pPTPL           pDF05                     L. lactis  NZ9800   (Field et al., 2008)           harbouring pDF05             E. coli  MC1000     E. coli  host for pPTPL   (O&#39;Driscoll et al., 2004)         E. coli  MC1000     E. coli  harbouring pPTPL   (O&#39;Driscoll et al., 2004)       pPTPL                 E. coli  Top10   Intermediate cloning host   Stratagene       Indicator organisms                 Strep. agalactiae     Nisin sensitive indicator   American Type Culture       ATCC13813                 Strep. mutans     Nisin sensitive indicator   Collection         S. dysgalactiae     Nisin sensitive indicator   UCC Culture Collection       ATCC43078                 S. aureus  NCDO 1499   Nisin sensitive indicator   American Type Culture         S. aureus  SA113   Nisin sensitive indicator   Collection         S. aureus  RF122   Nisin sensitive indicator   DPC Collection         S. aureus  Newman   Nisin sensitive indicator   UCC Culture Collection         S. aureus  DPC5247   Nisin sensitive indicator   UCC Culture Collection         S. aureus  ST528   Nisin sensitive indicator   UCC Culture Collection       (MRSA)                 S. aureus  ST530   Nisin sensitive indicator   DPC Collection       (MRSA)                 S. aureus  ST523   Nisin sensitive indicator   BSAC       (MRSA)               hVISA32679   Nisin sensitive indicator   BSAC       hVISA32652   Nisin sensitive indicator   BSAC       VRE Ec538   Nisin sensitive indicator   BSAC       VRE Ec295   Nisin sensitive indicator   BSAC       VRE Ec725   Nisin sensitive indicator   BSAC       VRE Ec533   Nisin sensitive indicator   BSAC       VRE Ec520   Nisin sensitive indicator   BSAC         L. monocytogenes     Nisin sensitive indicator   BSAC       10403S                 L. monocytogenes     Nisin sensitive indicator   BSAC       LO28                 L. monocytogenes     Nisin sensitive indicator   UCC Culture Collection       EGDeΔvirR                 L. monocytogenes     Nisin sensitive indicator   UCC Culture Collection       EGDeΔmprf                 L. lactis  ssp  cremoris     Nisin sensitive indicator   UCC Culture Collection       HP                 Lactococcus lactis     Nisin sensitive indicator   UCC Culture Collection       MG1363                 Micrococcus luteus     Nisin sensitive indicator   UCC Culture Collection         Bacillus cereus     Nisin sensitive indicator   UCC Culture Collection         Propionibacterium     Nisin sensitive indicator   UCC Culture Collection         acnes                   B. cereus  DPC 6088   Nisin sensitive indicator   UCC Culture Collection         B. cereus  DPC 6089   Nisin sensitive indicator   DPC Collection         E. durans  5133   Nisin sensitive indicator   DPC Collection         Bacillus cereus  IMF4   Infant milk formula   DPC Collection           (IMF isolate)             Staphylococcus     IMF isolate   UCC Culture Collection         hominis  IMF12                 Staphylococcus     IMF isolate   UCC Culture Collection         epidermidis  IMF54                 Bacillus firmus  IMF68   IMF isolate   UCC Culture Collection         Enterococcus durans     IMF isolate   UCC Culture Collection       IMF90                 Enterococcus faecium     IMF isolate   UCC Culture Collection       IMF91                 C. sakazakii  DPC6448   Indicator strain   UCC Culture Collection         C. sakazakii  DPC6445   Indicator strain   DPC Collection         C. sakazakii  DPC6444   Indicator strain   DPC Collection         C. sakazakii  DPC6443   Indicator strain   DPC Collection         C. sakazakii  DPC6442   Indicator strain   DPC Collection         C. sakazakii  DPC6441   Indicator strain   DPC Collection         C. sakazakii  DPC6522   Indicator strain   DPC Collection         C. sakazakii  DPC6524   Indicator strain   DPC Collection         C. sakazakii  DPC6440   Indicator strain   DPC Collection         C. sakazakii  DPC6442   Indicator strain   DPC Collection         C. sakazakii  DPC6446   Indicator strain   DPC Collection           Indicator strain   DPC Collection       Plasmids               pCI372   Cm R ; High-copy cloning   (Hayes et al., 1990)           vector           pDF05   pCI372 with nisA under    This study       pPTPL   its ownpromoter   (O&#39;Driscoll et al., 2004)       pDF03   Tet R ; lacZ; Low-copy   (Field et al., 2008)       pUC19   cloning vector           pDF04   pPTPL with nisA under   (Field et al., 2008)           its own promoter               AMP R ; lacZ; High-copy               cloning vector.               pUC19 with nisA under               its own promoter                    
Random Mutagenesis
 
     DNA obtained from  L. lactis  NZ9700 (Hoffmann et al., 2004) was used as template for the amplification of a 372 bp fragment encompassing the nisA gene with KOD polymerase (Novagen) using the primers oDF101 and oDF102. PCR amplicons were purified using the QIAquick PCR purification kit (QIAGEN Inc.), digested with BglII and XbaI (Roche) and cloned into similarly digested and Shrimp Alkaline Phosphatase (SAP; Roche) treated pPTPL. Following introduction into  E. coli  MC1000, plasmid was isolated from one clone and was sequenced (MWG Biotech, Germany) using the primer TETK P1 to ensure its integrity. The introduction of this plasmid, pDF03, into competent  L. lactis  NZ9800 successfully reinstated Nisin activity. To provide sufficient quantities of template DNA for error-prone PCR (ep-PCR), nisA was reamplified using pDF03 as template with KOD polymerase using the primers oDF101 and oDF103, digested with Xba1 and EcoR1 and cloned into similarly digested pUC19. Following introduction into  E. coli  Top 10 (Invitrogen), plasmid was isolated from one clone and was sequenced (MWG Biotech, Germany) using the primers M13FOR and M13REV to ensure its integrity. This plasmid, pDF04 was isolated from 100 ml overnight culture using the Maxi-prep plasmid kit (QIAGEN Inc.) to a concentration of approx 1,100 ng/μl. pDF04 was used as template for the Genemorph II random mutagenesis kit (Stratagene) according to manufacturer&#39;s guidelines. To introduce an average of one base change in the 372 bp cloned fragment, amplification was performed in a 50 μl reaction containing approximately 500 ng of target DNA (pDF04), 2.5 units Mutazyme DNA polymerase, 1 mM dNTPs and 200 ng each of primers oDF101 and oDF102. The reaction was preheated at 96° C. for 1 min, and then incubated for 22 cycles at 96° C. for 1 min, 52° C. for 1 min and 72° C. for 1 min, and then finished by incubating at 72° C. for 10 min. Amplified products were purified by gel extraction using the Qiaquick gel extraction kit (QIAGEN Inc), and reamplified with KOD polymerase before being digested with BglII and XbaI (Roche), ligated with similarly digested and SAP treated pPTPL and introduced into  E. coli  MC1000. To determine if the correct rate of mutation had been achieved recombinant plasmid DNA was isolated from selected clones using the QIAprep Spin miniprep kit (QIAGEN Inc) and sequenced (MWG Biotech). Transformants were pooled and stored in 80% glycerol at −20° C. Plasmid DNA isolated from the mutant bank was used to transform  L. lactis  NZ9800. Transformants (approx. 8000) were isolated from Q trays using the Genetix QPIX II-XT colony-picking robot and inoculated into 96 well plates containing GM17 freezing buffer, incubated overnight and subsequently stored at −20° C. 
     Saturation Mutagenesis 
     To generate a template for mutagenesis, the 372 base pair fragment encompassing the nisA gene was amplified with KOD polymerase using the primers oDF102 and oDF103, was digested and subsequently cloned into pCI372. Following introduction into  E. coli  Top 10 cells, plasmid was isolated from one clone and was sequenced (MWG Biotech, Germany) using the primer pCI372REV to ensure its integrity. Saturation mutagenesis of the serine codon at position 29 of nisA was carried out with pDF05 (pCI372-nisA) as template and using oligonucleotides NisS29deg FOR5′ Pho-TGTCATTGTNNKATTCACGTAAGCAAATAA 3′ and NisS29deg REV 5′ TACGTGAATMNNACAATGACAAGTTGCTGTTTTCATGTT 3′ containing an NNK codon in place of each native codon. PCR amplification was performed in a 50 μl reaction containing approximately 0.5 ng of target DNA (pDF05), 1 unit Phusion High-Fidelity DNA polymerase (Finnzymes, Finland), 1 mM dNTPs and 500 ng each of the appropriate forward and reverse oligonucleotide. The reaction was preheated at 98° C. for 2 mins, and then incubated for 29 cycles at 98° C. for 30 secs, 55° C. for 15 secs and 72° C. for 3 mins 30 secs, and then finished by incubating at 72° C. for 3 mins 30 secs. Amplified products were treated with Dpn1 (Stratagene) for 60 mins at 37° C. to digest template DNA and purified using the QIAquick PCR purification kit. Following transformation of  E. coli  Top 10 cells plasmid DNA was isolated and sequenced to verify that mutagenesis had taken place. The purified products were subsequently introduced by electroporation into the strain NZ9800 which has all the genes necessary for Nisin production. Approximately 180 transformants were chosen at random and inoculated into 96 well plates containing GM17 chloramphenicol, incubated overnight and stored at −20° C. after addition of 80% glycerol. A similar strategy was employed to carry out site saturation mutagenesis of residue 29 in Nisin Z, Nisin F and Nisin Q as well as the simultaneous saturation of residues 29 and 30 in Nisin A. 
     Nisin Purification 
       L. lactis  NZ9700 (Nisin A producer) or the mutant Nisin strain of interest was subcultured twice in GM17 broth at 1% at 30° C. before use. Two liters of modified TY broth were inoculated with the culture at 0.5% and incubated at 30° C. overnight. The culture was centrifuged at 7,000 rpm for 15 minutes. The cell pellet was resuspended in 300 mls of 70% isopropanol 0.1% TFA and stirred at room temperature for approximately 3 h. The cell debris was removed by centrifugation at 7,000 rpm for 15 minutes and the supernatant retained. The isopropanol was evaporated using a rotary evaporator (Buchi) and the sample pH adjusted to 4 before applying to a 10 g (60 ml) Varian C-18 Bond Elut Column (Varian, Harbor City, Calif.) pre-equilibrated with methanol and water. The columns were washed with 100 mls of 20% ethanol and the inhibitory activity was eluted in 100 mls of 70% IPA 0.1% TFA. 15 ml aliquots were concentrated to 2 ml through the removal of propan-2-ol by rotary evaporation. 1.5 ml aliquots were applied to a Phenomenex (Phenomenex, Cheshire, UK) C12 reverse phase (RP)-HPLC column (Jupiter 4u proteo 90 Å, 250×10.0 mm, 4 μm) previously equilibrated with 25% propan-2-ol, 0.1% trifluoroacetic acid TFA. The column was subsequently developed in a gradient of 30% propan-2-ol containing 0.1% TFA to 60% propan-2-ol containing 0.1% TFA from 10 to 45 minutes at a flow rate of 1.2 ml min −1 . 
     Mass Spectrometry 
     For Colony Mass Spectrometry (CMS) bacterial colonies were collected with sterile plastic loops and mixed with 50 μl of 70% isopropanol adjusted to pH 2 with HCl. The suspension was vortexed, the cells centrifuged in a benchtop centrifuge at 14,000 r.p.m. for 2 mins, and the supernatant was removed for analysis. Mass Spectrometry in all cases was performed with an Axima CFR plus MALDI TOF mass spectrometer (Shimadzu Biotech, Manchester, UK). A 0.5 μl aliquot of matrix solution (alpha-cyano-4-hydroxy cinnamic acid (CHCA), 10 mg ml −1  in 50% acetonitrile-0.1% (v/v) trifluoroacetic acid) was placed onto the target and left for 1-2 mins before being removed. The residual solution was then air-dried and the sample solution (resuspended lyophilised powder or CMS supernatant) was positioned onto the precoated sample spot. Matrix solution (0.5 μl) was added to the sample and allowed to air-dry. The sample was subsequently analysed in positive-ion reflectron mode. 
     Bioassays for Antimicrobial Activity 
     Deferred antagonism assays were performed by replicating strains on GM17 agar plates and allowing them to grow overnight before overlaying with either GM17/BHI/TSB-YE/MH agar (0.75% w/v agar) seeded with the appropriate indicator strain. For higher throughput screening of the S29X bank, deferred antagonism assays were performed by replicating strains using a 96 pin replicator (Boekel) or spotting 5 μl of a fresh overnight culture on GM17 agar plates and allowing them to grow overnight. Following overnight growth the strains were subjected to UV radiation for 30 minutes prior to overlaying with either GM17/BHI/TS/MH agar (0.75% w/v agar) seeded with the appropriate indicator 
     Minimum Inhibitory Concentration Assays 
     Minimum inhibitory concentration determinations were carried out in triplicate in 96 well microtitre plates. 96 well microtitre plates were pre-treated with bovine serum albumin (BSA) prior to addition of the peptides. Briefly, to each well of the microtitre plate 200 μL of phosphate buffered saline (PBS) containing 1% (w/v) bovine serum albumin (PBS/BSA) was added and incubated at 37° C. for 30 min. The wells were washed with 200 μL PBS and allowed to dry. Target strains were grown overnight in the appropriate conditions and medium, subcultured into fresh broth and allowed to grow to an OD 600  of  ˜ 0.5, diluted to a final concentration of 10 5  cfu ml −1  in a volume of 0.2 ml. Wild type Nisin and Nisin mutant peptides were adjusted to a 5 μM (hVISA), 2.5 μM (MRSA), 7.5 μM ( L. monocytogenes  10403S) or 500 nM ( L. lactis  strains) starting concentration and 2-fold serial dilutions of each peptide were added to the target strain. After incubation for 16 h at 37° C. the MIC was read as the lowest peptide concentration causing inhibition of visible growth. 
     Results 
     Creation and Screening of a Bank of Nisin A Derivatives 
     Screening of the Nisin mutants for enhanced bioactivity uses deferred antagonism assays which are performed by replicating strains on GM17 agar plates and allowing them to grow overnight before overlaying with either GM17/BHI/TSB-YE/MH agar (0.75% w/v agar) seeded with the appropriate indicator strain. The procedure is as follows: 
     A DNA fragment containing the nisA gene and its native P nis  promoter was amplified, and cloned into pPTPL (a reporter vector with a promoterless lacZ) to generate pDF03. This was subsequently introduced into  L. lactis  NZ9800. NZ9800 is derivative of a Nisin-producing strain,  L. lactis  NZ9700, from which the nisA gene has been deleted (Table 3). The heterologous expression of nisA from pDF03 successfully restored Nisin production to wildtype levels, confirming that this complementation system is suitable for expressing randomly mutagenized nisA genes. A second plasmid, pDF04 (pUC19-nisA), was used as a template for the generation of randomly mutated nisA fragments via mutazyme II PCR amplification (using conditions designed to achieve one nucleotide change on average per copy of nisA). These fragments were cloned into pPTPL and ultimately introduced into  L. lactis  NZ9800 resulting in a bank consisting of approximately 8000 potential variants. Screening of the bank was undertaken by way of deferred antagonism assays using two indicator strains  S. aureus  SA113 and  L. monocytogenes  LO28. One mutant colony tested exhibited an increased bioactivity against the two indicator strains. The exceptional strain exhibited an enhanced bioactivity (approx. 50% increase in zone size compared to the corresponding positive control) against  S. aureus  SA113 and  L. monocytogenes  LO28. Further testing of the mutant reveals enhanced bioactivity against  Lactococcus lactis  spp  cremoris  HP,  S. aureus  NCDO 1499 and  S. aureus  DPC5247. 
     Sequencing 
     DNA sequencing of the corresponding nisA gene revealed an alteration predicted to result in a change in residue 29 from a serine to glycine. 
     Site-Directed Mutagenesis 
     To determine if other Nisin A mutant derivatives that have been altered at amino acid 29 possess enhanced antimicrobial activity, site saturation mutagenesis of position 29 was carried out to generate a collection of such derivatives. A bank of approx 180 Nisin A S29X mutants was created. 
     The bank of 180 producers was screened against  Lactococcus lactis  HP and  S. aureus  DPC5247 and against  S. agalactiae  ATCC 13813 and  S. aureus  NCD01499 and a number of producers were found to produce zones of enhanced size relative to an unaltered control. 
     16 S29X mutants with enhanced activity were sent for mass spectrometric analysis which revealed the presence of 9 candidates producing a peptide of mass consistent with that of S29G as well as other peptides with masses of 3381, 3395, 3335 respectively. Sequencing of the corresponding genes confirmed that these masses correspond to S29G, as well as S29D (3381), S29E (3395) and S29A (3336). 
     Mass Spectrometry 
     Mass spectrometric analysis of 48 of the Nisin A mutants established that the residue at position 29 has been randomly altered as masses consistent with the following amino acid substitutions were observed: S29G, S29A, S29D, S29E, S29R, S29V, S29P, S29W, S29T, S29N, S291/L, S290, S29F, S29W. S29D, S29E, S29R, S29H, S29K. 
     The molecular weights of the Nisin A S29 derivatives as observed by mass spectrometry are listed in Table 5. In the case of S29C, colony mass spec did not yield a detectable mass. This mutant was identified by sequence analysis of colonies producing little/no detectable zone of inhibition. 
                                   TABLE 5                   Molecular weights of the Nisin A derivatives       of the current invention.            Amino acid   S29Predicted   Actual               N   3379.66   3379.05       Q   3393.69   3394.04       C   3368.70   Not detected (sequenced)       G   3322.60   3322.97       A   3336.64   3336.67       S   WT   3352.63       T   3366.66   3366.75       V   3364.69   3364.81       L   3378.71   3379.33       I   3378.71   3378.60       P   3362.67   3362.73       M   3396.74   3396.19       F   3412.73   3412.94       Y   3428.73   3429.17       W   3451.76   3451.61       D   3380.64   3381.32       E   3394.67   3395.56       R   3421.74   3421.93       H   3402.69   3404.81       K   3393.72   3394.16                    
Antimicrobial Activity of Nisin A Derivatives as Assessed by Deferred Antagonism Assays
 
     A collection of Nisin producers, in which the Nisin peptide encoding gene nisA has been randomly altered, were subjected to a screening study to identify Nisin derivatives with enhanced antimicrobial activity. 
     Nisin A S29G exhibits enhanced bioactivity, compared to a corresponding Nisin A producing control against a number of different strains. This was determined by deferred antagonism assays. 
     S29G is more active against  Listeria monocytogenes  L028 , L. monocyotgenes  10403s,  L. monocyotgenes  EGDe ΔvirR and  L. monocytogenes  EGDe Δmprf (the latter two being mutants of  L. monocytoenes  EGDe which exhibit an altered sensitivity to lantibiotics),  Lactococcus lactis  MG1363 , L. lactis  HP,  Bacillus cereus, Staphylococcus aureus  SA113 , S. aureus  DPC 5247 , S. aureus  NCD1499 , S. aureus  RF122 , S. aureus  Newman,  S. aureus  528 (MRSA),  S. aureus  530 (MRSA),  S. aureus  523 (MRSA), hVISA32652, hVISA32679 , S. agalactiae  ATCC13813 , Streptococcus dysgalactiae  43078, and  Streptococcus mutans , Vancomycin resistant  Eneterococcus  VRE Ec520, VRE Ec295, VRE Ec533, VRE Ec725, VRE Ec538 , Propionibacterium acnes , and  Micrococcus luteus  compared to Nisin A. 
     Nisin A S29A is more active against  L. lactis  MG1363 , L. lactis  HP,  S. aureus  SA113 , S. aureus  DPC 5247 , S. aureus  NCD01499 , S. mutans, S. agalactiae  ATCC13813 , S. aureus  528 (MRSA),  S. aureus  530 (MRSA), hVISA32652, hVISA32679 and  L. monocyotgenes  10403s compared to Nisin A. 
     Nisin A S29D is more active against  L. lactis  HP,  S. aureus  DPC 5247 , S. aureus  NCD01499 , S. agalactiae  ATCC13813 , Streptococcus mutans, Streptococcus dysgalactiae  43078 , S. aureus  Newman,  S. aureus  528 (MRSA),  S. aureus  523 (MRSA), VRE Ec295, VRE Ec725, VRE Ec538  Lactococcus lactis  MG1363 , L. lactis  HP,  Propionibacterium acnes, Bacillus cereus  and  Micrococcus luteus  compared to Nisin A. 
     Nisin A S29E are more active against  L. lactis  HP,  S. aureus  DPC 5247 , S. aureus  NCD01499 , Streptococcus  dysgalactiae 43078 , S. aureus  Newman, hVISA32652, Ec295, VRE Ec533  L. lactis  HP,  Propionibacterium acnes  and  Bacillus cereus  compared to Nisin A. 
     Broth-based MIC assays with purified peptides the S29G peptide possesses enhanced activity against  St. aureus  528 (MRSA),  St. aureus  530 (MRSA), hVISA 32679 , L. lactis  HP,  L. lactis  MG1363 and  L. monocytogenes  10403S compared to Nisin A. 
     The S29A peptide possesses enhanced activity against  St. aureus  528 (MRSA),  St. aureus  530 (MRSA), hVISA 32679 , L. lactis  HP,  L. lactis  MG1363 and  L. monocytogenes  10403S compared to Nisin A. 
     The S29D peptide possesses enhanced activity against  St. aureus  528 (MRSA),  L. lactis  HP and  L. lactis  MG1363 compared to Nisin A. 
     The S29E peptide possesses enhanced activity against  L. lactis  HP. 
     Minimum Inhibitory Concentration Assay 
     To assess if enhanced activity could be attributed to enhanced specific activity, broth-based minimum inhibitory concentration assays with purified peptides were carried out against selected strains. Results are given in micromolar values. Instances where antimicrobial activity is increased are indicated by bold text. 
                                                                           STRAIN   NisinA   S29G   S29A   S29D   S29E                                ST 528 a     0.156     0.078       0.078       0.078     0.156       ST 530 a     0.156     0.078       0.078     0.156   0.156       hVISA 32679 b     1.25     0.625       0.625     1.25    1.25          L. lactis  HP   0.062     0.031       0.015       0.015       0.015           L. lactis  1363   0.250     0.125       0.062       0.125     0.250         L. mono  10403S   3.75     1.875       1.875     3.75    3.75                  a Methicillin resistant  S. aureus .         b heterogenous Vancomycin insensitive  S. aureus              
Agarose-Based Diffusion Assays to Detect Bioactivity
 
     A modified agarose-based assay has been developed and has been found to be more sensitive when assessing bacteriocin activity from the supernatant of producing strains. The Nisin A S29 derivatives were retested using this assay (See  FIG. 1 ). 
     The modified agarose-based assay was performed against 2 indicator strains,  L. lactis  spp  cremoris  HP (Table. 6) and  Listeria monocytogenes  LO28 (Table. 7). 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Agarose-based diffusion assays of Nisin 
               
               
                 A S29 supernatants Vs  L. lactis  HP. 
               
             
          
           
               
                 Amino acid 
                   L. lactis  HP 
                   L. lactis  HP 
                   L. lactis  HP 
                 Average 
               
               
                 (S29X) 
                 (a) 
                 (b) 
                 (c) 
                 a + b + c 
               
               
                   
               
             
          
           
               
                 wt 
                 15.4 
                 15.4 
                 15.0 
                 15.26 
               
               
                 G 
                 15.5 
                 15.9 
                 14.8 
                 
                   
                     15.40 
                   
                 
               
               
                 A 
                 16.3 
                 16.9 
                 16.7 
                 
                   
                     16.63 
                   
                 
               
               
                 D 
                 19.8 
                 21.3 
                 19.9 
                 
                   
                     20.33 
                   
                 
               
               
                 Q 
                 15.3 
                 15.2 
                 15.4 
                 15.30 
               
               
                 N 
                 12.9 
                 13.5 
                 11.5 
                 12.63 
               
               
                 E 
                 18.7 
                 19.0 
                 18.3 
                 
                   
                     18.66 
                   
                 
               
               
                 C 
                 10.9 
                 11.3 
                 9.4 
                 10.53 
               
               
                 K 
                 8.9 
                 10.9 
                 9.8 
                  9.86 
               
               
                 T 
                 11.0 
                 12.9 
                 12.4 
                 12.1  
               
               
                 V 
                 11.7 
                 12.0 
                 11.2 
                 11.63 
               
               
                 L 
                 12.6 
                 13.5 
                 12.2 
                 12.76 
               
               
                 I 
                 9.2 
                 11.3 
                 9.2 
                 9.9 
               
               
                 W 
                 11.6 
                 13.5 
                 11.2 
                 12.1  
               
               
                 Y 
                 10.0 
                 11.3 
                 10.7 
                 10.66 
               
               
                 F 
                 10.6 
                 12.2 
                 10.2 
                 11.0  
               
               
                 M 
                 13.2 
                 14.5 
                 13.0 
                 13.56 
               
               
                 P 
                 13.3 
                 14.8 
                 12.9 
                 13.66 
               
               
                 R 
                 10.4 
                 11.5 
                 11.2 
                 11.03 
               
               
                 H 
                 11.2 
                 10.7 
                 10.9 
                 10.93 
               
               
                   
               
               
                 Measurement of inhibitory zone in mm 
               
             
          
         
       
     
     The results against  L. lactis  HP confirmed the previously identified enhanced Nisin A mutants S29G, S29A, S29D and S29E (highlighted above in bold underline). The results against  L. monocytogenes  LO28 established that just one of the 4 lead candidates, S29A, exhibited an enhanced phenotype against this target. Surprisingly, a derivative previously thought to be reduced in activity, Nisin A S29R (approx 50% reduced activity against HP), displayed an enhanced effect against  L. monocytogenes  LO28 (Table. 7). This result was confirmed in growth assays with serial dilutions of each S29 supernatant against  L. monocytogenes  LO28. (Data not shown) 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Agarose-based diffusion assays of selected Nisin 
               
               
                 A S29 supernatants Vs  L. monocytogenes  LO28. 
               
             
          
           
               
                   
                 S29 
                 LO28a 
                 LO28b 
                 Avg 
               
               
                   
               
             
          
           
               
                   
                 wt 
                 11.4 
                 11.1 
                 11.25 
               
               
                   
                 G 
                 10.1 
                 9.6 
                  9.85 
               
               
                   
                 A 
                 12.0 
                 12.5 
                 
                   12.25 
                 
               
               
                   
                 E 
                 10.5 
                 10.8 
                 10.65 
               
               
                   
                 D 
                 9.2 
                 9.0 
                  9.10 
               
               
                   
                 R 
                 11.2 
                 11.5 
                 
                   11.35 
                 
               
               
                   
               
             
          
         
       
     
     On the basis of the enhanced activity of Nisin A S29R against  L. monocytogenes  LO28, this peptide was selected to be included in further studies using purified peptides and MIC determination (Table. 8). It was decided to include the Nisin A M21V enhanced Nisin A derivative (also known as Nisin V) as a control. This peptide has previously been shown to display a two-fold increase in activity compared to wild-type against all strains tested in MIC assays. These studies confirmed the enhanced activity of Nisin A S29A and Nisin A S29R against  L. monocytogenes  LO28. 
                                                                                 TABLE 8                   Minimum Inhibitory concentrations of purified Nisin A S29       derivatives against  L. monocytogenes  LO28            Wt Nisin   M21V   S29G   S29A mg   S29E   S29D   S29R       mg l −1     mg l −1     mg l −1     l −1     mg l −1     mg l −1     mg l −1         (μM)   (μM)   (μM)   (μM)   (μM)   (μM)   (μM)                    6.28     3.14     6.28     3.14     6.28   12.56     3.14         (1.875)     (0.937)     (1.875)     (0.937)     (1.875)   (3.75)     (0.937)                      
Minimum Inhibitory Concentration Assay
 
     The sensitivity of a greater variety of target strains to the lead Nisin A S29 derivatives, including in some instances S29R, was assessed using the MIC approach. Results (Table. 8) are given in micromolar values. Instances where antimicrobial activity is increased are indicated by bold text. 
                                                                                 TABLE 8                   Minimum inhibitory activity (micromolar values) of Nisin A       S29 derivatives against a selection of strains            STRAIN   NisinA   S29G   S29A   S29D   S29E   S29R                    ST 528 a     0.156     0.078       0.078       0.078     0.156   Nd       ST 530 a     0.156     0.078       0.078     0.156   0.156   Nd       hVISA 32679 b     1.25     0.625       0.625     1.25   1.25   Nd         L. lactis  HP   0.062     0.031       0.015       0.015       0.015     0.125         L. lactis  MG1363   0.250     0.125       0.062       0.125     0.250   Nd         L. mono  10403S   3.75     1.875       1.875     3.75   3.75   Nd         L. mono  LO28   1.875   1.875     0.937     3.75   1.875     0.937           S. aureus  RF122   0.312     0.156       0.156     1.25   0.625   Nd         S. mutans     2.5   2.5     1.25     5.0     1.25     5.0         B. cereus  DPC 6088   2.5     1.25       0.612     5.0   1.25   2.5         B. cereus  DPC 6089   2.5     1.25       1.25     2.5     1.25     2.5         E. durans  5133   0.156     0.078       0.039     0.156     0.156     0.156                 a Methicillin resistant  S. aureus .         b heterogenous Vancomycin insensitive  S. aureus .       nd = not determined            
Growth Curve Analysis
 
     The adoption of a modified growth assay (peptides are incubated with strains in sodium phosphate buffer for 3 hours prior to spectrophotometer analysis) provided a more sensitive means of assessing the antimicrobial effect of peptides on some bacterial strains. 
     A Gram negative strain  Cronobacter sakazakii  DPC 6440 was used as indicator in growth assays with wild-type peptide and the lead Nisin derivatives S29G, S29A, S29E, and S29D. The derivatives S29D and S29E displayed equal or less activity respectively than the wild-type peptide (data not shown), while S29G and S29A completely inhibited the growth of  C. sakazakii . Triplicate plate counts taken at 24 hours revealed 1×10 9    C. sakazakii  for the wild-type but no detectable cell numbers for either S29G and S29A ( FIG. 2 ). 
     This is a significant break-through as Nisin, and indeed lantibiotics in general, are not noted for their activity against Gram negative bacteria (NB. Existing Nisin variants of note such as M21V [Nisin V] did not exhibit this potent anti- C. sakazakii  activity). 
       FIG. 2  shows growth curve analysis of purified Nisin A and Nisin A S29G and S29A derivatives against  C. sakazakii  DPC6440(1×10 5  initial inoculum) at 100 μg/ml final concentration. Results are representative of triplicate assays. The enhanced activity of these derivatives, and of Nisin A S29R, is also evident at a 30 μM final concentration. 
     Kill Curve Analysis of S29 Derivatives Against  C. sakazakii    
     On the basis of growth curve and well assay analysis, kill curves were carried out using two concentrations of wild-type and S29G, S29A and S29R peptides (Table 9). 
                                                             TABLE 9                   Kill curve (1 hr) results of Nisin S29 mutants and       Wt against  C. sakazakii  DPC 6440 (1 × 10 5 ).                54 μM   30 μM   6 μM                        Nisin A   1.0 × 10 4     4.0 × 10 3         8 × 103           S29G   3.0 × 10 2         5 × 10 2     1.0 × 103           S29A       7 × 10 2     1.0 × 10 2         6 × 102           S29R   2.0 × 10 3     1.6 × 10 3     1.0 × 103                    
Additional  C. sakazakii  Isolates from Powdered Infant Formula (PIF)
 
     Modified agarose assays were carried out with 11 additional  C. sakazakii . For this assay resuspended purified peptide is inoculated into wells which have been bored in the appropriate solid media plates (to which has been added the phosphate buffer washed indicator strain at a concentration of approx. 1×10 7 ) and allowed to incubate for 3 hours prior to overlay and overnight incubation at the desired temperature. 
     Modified Agarose Assay Method: 
     The media is made up fresh, autoclaved (121° C. for 15 mins) and cooled to 50° C. prior to use as follows: LB underlay 100 ml sodium phosphate buffer, 0.03 g LB, 1 g agarose and 20 uL Tween 20. LB Overlay: 100 ml H2O 5 g LB and 1 g agarose. 
     A fresh overnight of the target indicator is re-inoculated (2%) and allowed to grow for approx 3 hours to early log phase (OD  ˜ 0.3). 1 ml early log phase cells are washed twice in sodium phosphate buffer by centrifuging at 12,000 rpm for 6 min. The cells are resuspended in 1 ml buffer to reach a final concentration of approx 1×10 7 . 100 μl of cells are added to 15 mls of LB underlay, poured into a small petri dish (9 cm) and allowed to set to form a uniform layer before punching wells (approx 5 mm) in the media. 10 μl of peptide is added at the desired concentration (30 μM) and the plates incubated at the appropriate temperature (i.e 37° C.) for 3 hours. Following this, the plates are overlayed with 15 mls of media (i.e. LB overlay), allowed to set and incubated at the appropriate temperature for 24 hours. Zones are measured using a vernier callipers after 24 hours. 
     Those peptides displaying enhanced activity are indicated by bold text. 
     
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 Modified agarose assays of Nisin derivatives against  C. sakazakii   
               
               
                 PIF isolates (values represent zone size in mm) 
               
             
          
           
               
                 
                   Cronobacter sakazakii 
                 
                   
                   
                   
                   
                   
                   
               
               
                 strain 
                 NisinA 
                 S29G 
                 S29A 
                 S29D 
                 S29E 
                 S29R 
               
               
                   
               
             
          
           
               
                 DPC 6448 
                 8.4 
                 
                   9.8 
                 
                 
                   10.4 
                 
                 8.3 
                 
                   12.3 
                 
                 8.0  
               
               
                 DPC6445 
                 nz 
                 Nz 
                 nz 
                 nz 
                 nz 
                 nz 
               
               
                 DPC6444 
                 6.2 
                 
                   6.3 
                 
                 
                   6.8 
                 
                 nz 
                 8.6hazy 
                 nz 
               
               
                 DPC6443 
                 nz 
                 
                   6.4 
                 
                 
                   6.8 
                 
                 nz 
                 
                   7.4 
                 
                 nz 
               
               
                 DPC6442 
                 8.0 
                 
                   9.5 
                 
                 
                   9.4 
                 
                 7.4 
                 
                   8.6 
                 
                 nz 
               
               
                 DPC6441 
                 nz 
                 
                   7.5 
                 
                 
                   8.2 
                 
                 nz 
                 9.0 
                 nz 
               
               
                 DPC6522 
                 nz 
                 
                   7.5 
                 
                 
                   7.7 
                 
                 nz 
                 8.0hazy 
                 nz 
               
               
                 DPC 6440 
                 6.53 
                 
                   7.56 
                 
                 
                   7.50 
                 
                 nz 
                 6.96 
                 
                   7.03 
                 
               
               
                 DPC6442 
                 10.1 
                 
                   11.16 
                 
                 
                   11.40 
                 
                 9.90 
                 10.13 
                 9.13 
               
               
                 DPC6446 
                 10.03 
                 
                   11.06 
                 
                 
                   10.40 
                 
                 
                   10.83 
                 
                 
                   11.06 
                 
                 9.06 
               
               
                 DPC6524 
                 8.93 
                 
                   9.63 
                 
                 
                   9.10 
                 
                 8.83 
                 8.92 
                 7.60 
               
               
                   
               
               
                 nz = no zone of inhibition 
               
             
          
         
       
     
     The results indicate that Nisin A S29G and S29A are consistently better than Nisin A against  C. sakazakii  isolates, with Nisin A S29D, S29E and S29R being enhanced in some instances. 
     Activity Against Additional Infant Milk Formula (IMF) Isolates 
     Standard deferred antagonism (spot on lawn) assays were performed on 7 isolates from infant milk formula Table. 11 
                                                                                 TABLE 11                   Assessment of the activity Nisin A S29 derivatives against a       selection of other infant milk formula associated strains                NisinA   S29G   S29A   S29D   S29E   S29R       STRAIN   (mm)   (mm)   (mm)   (mm)   (mm)   (mm)                      Bacillus cereus  IMF4   7.5     8.1       8.6     NZ   7.2   7.2         Staphylococcus     18.5     19.6       20.8       20.0     17.6   13.7         hominis  IMF12         Staphylococcus     10.0     12.3       12.1     6.9   9.4   7.9         epidermidis  IMF54         Bacillus firmus  IMF68   18.8   18.0     19.6       20.3     18.3   13.9         Enterococcus durans     16.3     17.8       16.6       17.9       17.3     9.4       IMF90         Enterococcus faecium     14.1     17.0       16.4       16.5     10.8   9.3       IMF91               Average of duplicate results            
Nisin A, Z, F and Q Mutants
 
Saturation of Serine-29 in Nisin A, Z, F and Q Backgrounds and S29-I30 Combination in Nisin A Background
 
Nisin A S29 Derivatives
 
     As has been previously outlined, randomization of the codon at serine 29 of the nisA gene produced several derivatives with enhanced bioactivity namely S29G, S29A, S29D, S29E and S29R. The latter was recently discovered through the use of a modified overlay and growth curve assay using producing strain supernatants. 
       FIGS. 1 and 3  shows the results of deferred antagonism assays of NisinA-S29X variants against  L. lactis  HP. Amino acid changes are indicated by the single letter code and were determined by Mass Spectrometry. The symbol * denotes amino acid change determined by DNA sequence analysis. 
     Nisin Z S29X Derivatives 
     Saturation mutagenesis of the serine codon at position 29 of nisZ was carried out with pDF05 (pCI372-nisA) as template and using oligonucleotides NisZS29deg FOR5′ Pho-GCA ACT TGT  AAC  TGT NNK ATT CAC GTA AGC AAA TAA TCT AGA and NisZS29deg REV 5′ GCT TAC GTG AAT MNN ACA  GTT  ACA AGT TGC TGT TTT CAT GTT containing an NNK codon in place of each native codon (codons to alter His27Asn are underlined). The purified products were subsequently introduced by electroporation into the strain NZ9800 which has all the genes necessary for Nisin production. Approximately 180 transformants were chosen at random and inoculated into 96 well plates containing GM17 chloramphenicol, incubated overnight and stored at −20° C. after addition of 80% glycerol. 
     Screening of the bank was carried out using deferred antagonism assays using  Lactococcus lactis  HP,  S. aureus  RF122 ( FIG. 4 ) and  Listeria monocytogenes  LO28. 
       FIG. 4 . Deferred antagonism assays of NisinZ-S29X variants against  S. aureus  RF122 and  L. lactis  HP. Amino acid changes are indicated by the single letter code and were determined by Mass Spectrometry. * denotes amino acid change determined by DNA sequence analysis. 
     Summary 
     S29G and S29A derivatives are still enhanced in the Nisin Z background when tested against both strains  L. lactis  HP and  S. aureus  RF122. Interestingly, Nisin A was included as a control and it is observed that Nisin A&lt;Nisin Z&lt;NisinZ S29A/S29G when tested against  S. aureus  RF122. The apparent lack of activity of NisinZ-S29G against  L. lactis  HP is still under investigation. The Nisin Z S29E, S29D but also S29N derivatives show enhanced activity against  L. lactis  HP which for S29E and S29D is also observed in the Nisin A background. However, S29N in Nisin A is not enhanced. 
     Nisin F S29X Derivatives 
     Saturation mutagenesis of the serine codon at position 29 of nisZ was carried out with pDF05 (pCI372-nisA) as template and using oligonucleotides NisFS29deg FOR5′ Pho-GCA ACT TGT  AAC  TGT NNK  GTT  CAC GTA AGC AAA TAA TCT AGA and NisFS29deg REV 5′ GCT TAC GTG  AAC  MNN ACA  GTT  ACA AGT TGC TGT TTT CAT GTT containing an NNK codon in place of each native codon (codon changes for H27N and I30V are underlined). The purified products were subsequently introduced by electroporation into the strain NZ9800 which has all the genes necessary for Nisin production. Approximately 180 transformants were chosen at random and inoculated into 96 well plates containing GM17 chloramphenicol, incubated overnight and stored at −20° C. after addition of 80% glycerol. 
     Screening of the bank was carried out using deferred antagonism assays using  Lactococcus lactis  HP ( FIG. 5 ),  S. aureus  RF122 and  Listeria monocytogenes  LO28. 
       FIG. 5  shows the results of deferred antagonism assays of NisinF-S29X variants against  L. lactis  HP. Amino acid changes are indicated by the single letter code and were determined by Mass Spectrometry. The symbol * denotes amino acid change determined by DNA sequence analysis. 
     Summary 
     S29E and S29A derivatives are still enhanced in the Nisin F background when tested against the strain  L. lactis  HP. Wild-type Nisin A was included as a control and it is observed that Nisin A&lt;Nisin F&lt;Nisin F S29E, and S29A. Moreover, S29V and S29N are enhanced in the Nisin F background, while S29D could not be detected. Importantly, Nisin F S29G appears to be greatly reduced in activity. A mass corresponding to S29G was observed several times, yet all exhibited little/no activity. The reason for this is not yet apparent, though S29G in the Nisin Z background also displayed poor activity against  L. lactis  HP only ( FIG. 4 ). 
     Nisin Q S29X Derivatives 
     Saturation mutagenesis of the serine codon at position 29 of nisQ was carried out with pC1372-nisQ as template and using oligonucleotides NisFS29deg FOR5′ Pho-GCA ACT TGT  AAC  TGT NNK  GTT  CAC GTA AGC AAA TAA TCT AGA 3′ and NisQS29deg REV 5′ GCT TAC GTG  AAC  MNN ACA  GTT  ACA AGT TGC TGT TTT  CAG  3′ containing an NNK codon in place of each native codon (codon changes for H27N and I30V and M21L are underlined). The purified products were subsequently introduced by electroporation into the strain NZ9800 which has all the genes necessary for Nisin production. Approximately 180 transformants were chosen at random and inoculated into 96 well plates containing GM17 chloramphenicol, incubated overnight and stored at −20° C. after addition of 80% glycerol. 
     Screening of the bank was carried out using deferred antagonism assays using  Lactococcus lactis  HP ( FIG. 6 ),  S. aureus  RF122 and  Listeria monocytogenes  LO28. 
       FIG. 6 . Deferred antagonism assays of NisinQ-S29X variants against  L. lactis  HP. Amino acid changes are indicated by the single letter code and were determined by Mass Spectrometry. 
     denotes amino acid change determined by DNA sequence analysis. 
     Summary 
     The Nisin Q S29D, S29E and S29A derivatives all show enhanced activity against  L. lactis  HP. S29A is also enhanced against  S. aureus  RF122. Interestingly, Nisin Q S29G exhibits very reduced activity ( FIG. 6 ) and this was also found to be the case for Nisin F S29G ( FIG. 5 ). Given that Nisin F and Nisin Q are identical at the C-terminus (H27N, I30V), amino acid substitutions at serine 29 would be expected to have similar outcomes for bioactivity in each case. Indeed, enhanced derivatives S29D, S29E, S29A are detected in each background. One exception appears to be Nisin F S29V which exhibits enhanced activity, while Nisin Q S29V exhibits a wild-type phenotype. In contrast, S29P exhibits an enhanced phenotype in the Nisin Q, but not Nisin F backgrounds. 
     The consequences, with respect to the mass of the peptode produced, of subjecting Nisin A, Z, F and Q to saturation mutagenesis at position 29 are summarised in Table 12. 
                                           TABLE 12                   S29X derivatives identified in NisinA,       NisinZ, NisinF and NisinQ backgrounds.            Amino                       acid   NisinA-S29X   NisinZ-S29X   NisinF-S29X   NisinQ-S29X               N   3379.66   3358.92   3341.45   nd       Q   3393.69   3372.41   Nd   3367.38       C   3368.70   Nd   Nd   nd       G   3322.60   3300.64   3286.77   3299.07       A   3336.64   3314.55   3299.41   3311.85       S   3353.15   3331.63   3316.85   3327.50           (WT)   (WT)   (WT)   (WT)       T   3366.66   3344.91   3329.03   3342.64       V   3364.69   3343.08   3327.44   3340.10       L   3378.71   3356.42   3341.95   3353.85       I   3378.71   3356.06   3340.50   3353.85       P   3362.67   3341.27   3326.56   3338.64       M   3396.74   3374.82   3360.86   nd       F   3412.73   3390.79   3376.40   nd       Y   3428.73   3407.16   3394.39   3403.74       W   3451.76   3429.48   3415.04   nd       D   3380.64   3355.30   3343.60   3354.11       E   3394.67   3373.15   3357.93   3367.97       R   3421.74   3399.69   3385.13   3397.29       H   3402.69   Nd   3364.28   3376.93       K   3393.72   3372.66   Nd   nd               nd—derivative not detected            
Nisin A S29XX Derivatives (in which Serine 29 and Isoleucine 30 are Randomized Together).
 
     As a consequence of the altered activity of serine 29 derivatives in the Nisin F background (which differs from Nisin A at positions 27 and 30: His27Asn, Ile30Val), randomization of serine 29 and isoleucine 30 in combination was carried out in the Nisin A background. 
     Saturation mutagenesis of the serine and isoleucine codons at position 29 and 30 respectively of nisA was carried out with pDF05 (pCI372-nisA) as template and using oligonucleotides NisAS29XXdeg FOR5′ Pho-TGT CAT TGT NNK NNK CAC GTA AGC AAA TAA TCT AGA and NisAS29XXdeg REV 5′ GCT TAC GTG MNN MNN ACA TAG ACA AGT TGC TGT TTT CAT GTT containing an NNK codon in place of each native codon. The purified products were subsequently introduced by electroporation into the strain NZ9800 which has all the genes necessary for Nisin production. Approximately 2000 transformants were chosen at random and inoculated into 96 well plates containing GM17 freezing buffer with chloramphenicol (10 μg/ml) incubated overnight and stored at −20° C. 
     Screening of the bank was carried out using deferred antagonism assays using  Lactococcus lactis  HP, and  S. aureus  RF122 ( FIG. 7 ). 
       FIG. 7  shows the results of deferred antagonism assays of select NisinA-S29XX variants against  L. lactis  HP and  S. aureus  RF122. The symbol * denotes amino acid change determined by DNA sequence analysis. 
     Summary 
     From the approximately 2000 mutants screened, 10 mutants exhibiting the strongest zones of inhibition (against one or all the indicator strains tested) were selected for DNA sequence analysis as mass spectrometry alone cannot be used to determine amino acid substitutions where two or more codons are altered simultaneously. The amino acid substitutions and target strain activity in each case are listed in Table. 13. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 13 
               
             
             
               
                   
               
               
                 Nisin 29-30 mutants generated through saturation mutagenesis 
               
               
                 which show potent antimicrobial activity. 
               
             
          
           
               
                   
                   
                 
                   L. lactis 
                 
                 
                   S. aureus 
                 
                 
                   L. mono 
                 
               
               
                 Serine29X 
                 Isoleucine30X 
                 HP 
                 RF122 
                 LO28 
               
               
                   
               
               
                 D 
                 V 
                 ✓ 
                   
                   
               
               
                 D 
                 L 
                 ✓ 
                   
                   
               
               
                 D 
                 I 
                 ✓ 
                 ✓ 
                 ✓ 
               
               
                 A 
                 V 
                   
                 ✓ 
                   
               
               
                 E 
                 L 
                 ✓ 
                 ✓ 
                 ✓ 
               
               
                 E 
                 A 
                 ✓ 
                   
                   
               
               
                 S 
                 G 
                 ✓ 
                   
                   
               
               
                 S 
                 V 
                 ✓ 
                 ✓ 
                 ✓ 
               
               
                 N 
                 L 
                 ✓ 
               
               
                   
               
             
          
         
       
     
     These investigations further highlight the benefits in many instances of having an alanine (A), aspartate (D), glutamate (E), or asparagine (N). Among the combinations generated were those noted above as being enhanced i.e. DI, corresponding to the Ser29Asp derivative of Nisin A, and DV, corresponding to the Ser29Asp derivative of Nisin F, and AV, corresponding to the Ser29Ala derivative of Nisin F. 
     Alanine at position 29 was also detected, in combination with valine 30, which correlates with an equivalent Nisin F S29A derivative exhibiting enhanced activity ( FIG. 5 .) 
     The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. 
     It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.