bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of enterobacteria and Listeria growth by lactic, acetic and formic acids
Authors: östling Charlotta E. , Lindgren S. E.
Published: March 2008

Minimum inhibitory concentrations (MIC) of undissociated lactic, acetic and formic acids were evaluated for 23 strains of enterobacteria and two of Listeria monocytogenes. The evaluation was performed aerobically and anaerobically in a liquid test system at pH intervals of between 4.2 and 5.4. Growth of the enterobacteria was inhibited at 2–11 mmol 1−1, 0.5–14 mmol 1−1 and 0.1–1.5 mmol 1−1 of undissociated lactic, acetic and formic acids, respectively. The MIC value was slightly lower with anaerobic conditions compared with aerobic conditions. The influence of protons on the inhibition was observed for acetic acid at the low pH values. Undissociated lactic acid was 2 to 5 times more efficient in inhibiting L. monocytogenes than enterobacteria. Acetic acid had a similar inhibitory action on L. monocytogenes compared with enterobacteria. Inorganic acid (HCl) inhibited most enterobacteria at pH 4.0; some strains, however, were able to initiate growth to pH 3.8. The results indicate that the values of undissociated acid which occur in a silage of pH 4.1–4.5 are about 10–100 times higher than required in order to protect the forage from the growth of enterobacteria and L. monocytogenes.
Classification of the spoilage flora of raw and pasteurized bovine milk, with special reference to Pseudomonas and Bacillus
Authors: Ternström A. , Lindberg A.‐M. , Molin G.
Published: March 2008

Eighty‐one bacterial strains isolated from refrigerated raw milk, 124 from pasteurized milk and cream stored at 5°C and 7°C, and 19 type and reference strains of Pseudomonas spp. and Bacillus spp. were characterized by numerical phenotypic analysis. Data were processed with simple matching (SSM) and Jaccard (SJ) coefficients, and UPGMA clustering. Fourteen clusters of Gram‐negative bacteria were formed at SJ= 79% (SSM= 90%). Raw milk was exclusively spoilt by Gram‐negative bacteria, the majority of which were Pseudomonas fluorescens biovar I, Ps. fragi, Ps. lundensis and Ps. fluorescens biovar III. Minor groups in raw milk included Enterobacteriaceae spp. and Acinetobacter spp. Pasteurized milk was spoilt by essentially the same Gram‐negative organisms in 65% (5°C) and 50% (7°C) of the cases. The phenotypic characteristics of Gram‐negative bacteria are given. Bacillus polymyxa (both temperatures) and B. cereus (only at 7°C) were responsible for 77% of samples spoiled by the Gram‐positive organisms. Minor milk spoilage groups included other Bacillus spp. and lactic acid bacteria. All Bacillus spp. grew fermentatively in milk, and most strains denitrified. It is suggested that: (i) industrial recontamination tests of pasteurized milk are directed against Pseudomonas; (ii) milk is stored at 5°C or lower to avoid growth of B. cereus; and (iii) the significance of gas‐producing and nitrate/nitrite‐reducing Bacillus strains is recognized in cheese production.
Occurrence of campylobacters in small domestic and laboratory animals
Authors: Moreno G.S. , Griffiths P.L. , Connerton I.F. , Park R.W.A.
Published: March 2008

Faeces samples from 156 healthy domestic pets and laboratory animals were examined for campylobacters with both a selective medium (Campylobacter Blood Free Medium; Oxoid, CM739) and selective filtration through a 0.65 μm pore size filter. Campylobacter spp. were isolated from 78 of the samples; filtration was the most effective method. Isolates were characterized by biochemical tests and DNA/DNA hybridization with whole chromosomal DNA from reference strains as probes. Campylobacter upsaliensis was the most common species isolated from cats (45 from 68 samples) whilst Camp. jejuni was more often isolated from dogs (19 from 56 samples). More attention should be paid to pets as a potential source of campylobacters capable of causing diarrhoea in human beings. Procedures other than those involving currently‐used selective agents must be employed to efficiently detect all campylobacters.
In vitro susceptibility of Clostridium perfringens isolated from farm animals to growth‐enhancing antibiotics
Authors: Devriese L.A. , Daube G. , Hommez J. , Haesebrouck F.
Published: March 2008

Minimal inhibitory concentration (MIC) determinations were carried out with seven growth‐enhancing antibiotics against 95 Clostridium perfringens field isolates obtained during 1991 and 1992 from poultry, pigs and calves. All were resistant to 64 μg ml−1 of the bambermycin antibiotic, flavomycin (flavophospholipol) and susceptible to avoparcin (MIC90 0.25 μg ml−1), avilamycin (MIC90 0.5 μg ml−1) and salinomycin (MIC90≤ 0.12 μg ml−1). Acquired resistance against bacitracin was detected in some isolates from poultry and bovines and resistance to tylosin and virginiamycin in some strains from all species investigated. Overall, the prevalence of resistance was comparable to the low levels recorded in 1979 in Cl. perfringens isolates from the same animal host species.
Revival of biocide‐treated spores of Bacillus subtilis
Authors: Williams Nicola D. , Russell A.D.
Published: March 2008

Spores of Bacillus subtilis NCTC 8236 were treated with biocides and then subjected to various revival procedures. Sodium hydroxide (optimum concentration 25 mmol 1−1) revived a small portion of glutaraldehyde‐treated spores but not of spores exposed to formaldehyde, polyvinylpyrrolidone‐iodine (PVP‐I), Lugol's iodine, sodium hypochlorite or sodium dichloroisocyanurate (NaDCC). Post‐treatment heat shock (at 70° or 80°C) increased the numbers of colony‐forming units (cfu) of formaldehyde‐injured spores. Coat‐extraction procedures had the greatest effect on iodine‐pretreated spores. The uptake of iodine and chlorine was more rapid and occurred to a greater extent with outgrowing, germinating and especially coat‐deficient spores than with mature, resting spores.
A new method for the concentration of Cryptosporidium oocysts from water
Authors: Vesey G. , Slade J.S. , Byrne M. , Shepherd K. , Fricker C.R.
Published: March 2008

A novel method for the concentration of Cryptosporidium oocysts from water has been developed, based upon the precipitation of calcium carbonate. A 10 1 water sample is treated by adding solutions of calcium chloride and sodium bicarbonate and raising the pH value to 10 with sodium hydroxide. Crystals of calcium carbonate form and enmesh particles in the Cryptosporidium oocyst size range. The crystals are allowed to settle, the supernatant fluid is discarded and the calcium carbonate precipitate dissolved in sulphamic acid. The sample can be concentrated further by centrifugation. Recoveries of oocysts from seeded samples of deionized, tap and river water were in excess of 68%.
Time‐resolved fluoroimmunoassay as a method for detection of Erwinia chrysanthemi in potato peel extracts
Authors: van der Wolf J.M.
Published: March 2008

J.M. VAN DER WOLF. 1993. Time‐resolved fluoroimmunoassay (TR‐FIA) was compared with double antibody sandwich (DAS)‐ELISA for detection of Erwinia chrysanthemi antigens in potato peel extracts. Pure cultures were used to optimize TR‐FIA with respect to the microplate washing procedure and dilution buffer compositions.

The detection threshold level for spiked potato peel extracts with the optimized TR‐FIA format was 105 cells ml‐1 as for the detection level of DAS‐ELISA. The signal to background ratios at concentrations above 105 cells ml‐1 were higher with TR‐FIA than with DAS‐ELISA. The dynamic range of TR‐FIA was also superior to that of DAS‐ELISA.

It can be concluded that TR‐FIA is an attractive alternative to DAS‐ELISA as a detection method for Erw. chrysanthemi, especially when quantification is required.
Enterocin 226NWC, a bacteriocin produced by Enterococcus faecalis 226, active against Listeria monocytogenes
Authors: Villani F. , Salzano G. , Sorrentino Elena , Pepe Olimpia , Marino P. , Coppola S.
Published: March 2008

F. VILLANI, G. SALZANO, E. SORRENTINO, O. PEPE, P. MARINO AND S. COPPOLA. 1993. Enterococcus faecalis 226, isolated from natural whey cultures utilized as starters in the manufacture of mozzarella cheese from water‐buffalo milk, produces a bacteriocin designated enterocin 226NWC. The bacteriocin was isolated from culture supernatant fluids of the producer strain and was active against strains of the same species and Listeria monocytogenes, but not against useful lactic acid bacteria. Enterocin 226NWC is a protein with an apparent molecular weight of about 5800; it is relatively heat‐stable and has a bactericidal mode of action. Listeria monocytogenes, growing in the presence of the enterocin 226NWC producer strain in broth and in reconstituted skim milk, was inhibited.
A laboratory apparatus for the generation and biocide efficacy testing of Legionella biofilms
Authors: Green P.N. , Pirrie R.S.
Published: March 2008

P.N. GREEN AND R.S. PIRRIE. 1993. The construction and operation of a laboratory biofilm generator designed to grow sessile populations of legionellas for biocide efficacy testing is described. Some examples of static biocide testing on both sessile and planktonic populations of Legionella bozemanii are discussed along with other potential applications of the apparatus.
Characterization of bacteriocin produced by Pediococcus pentosaceus from wine
Authors: de Saad Ana M. Strasser , de Nadra María C. Manca
Published: March 2008

A.M. STRASSER DE SAAD AND M.C. MANCA DE NADRA. 1993. Twenty strains of Pediococcus pentosaceus isolated from wine were examined for production of bacteriocins. Only two of them showed inhibitory activity, Ped. pentosaceus N4p against the indicator strains of the same species and N5p against 19 strains of the three genera of lactic acid bacteria from wine. The antimicrobial substance from N5p strains was removed by membrane (0.2 μm) filtration, destroyed by organic solvents and proteolytic enzymes. It was stable for 60 min at 100d̀C. The bacteriocin was produced early in the growth cycle and its production was maximum after 48 h of culture in tomato juice medium at an initial pH of 6.5. The bactericidal effect was observed.
Comparison of Signal and Bactec NR‐660 blood culture systems
Authors: Stevens M. , Prentice M.B. , Swann R.A. , Mitchell C.J. , Donkin A.
Published: March 2008

M. STEVENS, M.B. PRENTICE, R.A. SWANN, C.J. MITCHELL AND A. DONKIN. 1993. The Signal blood culture system was compared with the Bactec NR‐660. A total of 1617 blood culture sets yielded 143 (8.8%) significant isolates; 113 (79.0%) were from positive bottles in both the Bactec and Signal systems. Twelve organisms (8.4%) were detected and isolated from the Signal system only and another 18 (12.6%) from the Bactec system only. Of these 18, five were Signal‐positive but the organism was not recovered and four organisms were isolated from negative Signal bottles on terminal subculture. The time taken to detection for each system was similar; the Signal system detected 68% and the Bactec 63% of significant positives within 24 h. At 48 h Bactec detected 91% and the Signal 85%. A significantly‐reduced number of bottles which gave a positive signal but were negative by microscopical and cultural methods was found, compared with previous reports. The 1 h incubation period prior to the insertion of the Signal growth indicator device was considered to be the cause of this reduction in the proportion of false positives.

Fifty‐five percent (42/77) of the Bactec false positives were due to delta growth value. This is when there is an increase in the growth index of ≥ 15 without the positive threshold level of 30 being attained. This occurred in the anaerobic bottle on day 2 with 42 bottles. Another 40% (31/77) of the false positives had a growth value between the positive threshold of 30 and a value of 35.

Eighty (4.9%) of Bactec and 65 (4.0%) of Signal sets yielded clinically non‐significant isolates. Although the yield of significant isolates for the two systems was similar, Signal failed to detect a small number of medically important organisms without subculture.
Heat resistance of Listeria monocytogenes by two recovery media used with and without cold preincubation
Authors: Sörqvist S.
Published: March 2008

S. SÖRQVIST. 1993. Three strains of Listeria monocytogenes were heat‐treated at three temperatures in physiological saline by a capillary tube method. Recovery of heat‐treated bacteria was performed on blood agar and on tryptose phosphate agar with ferric citrate and aesculin (TPA‐FE). Both media were used in two ways: (1) incubation at 37d̀C for 7 d, and (2) preincubation at 4d̀C for 5 d in order to obtain repair of heat‐injured bacteria, followed by incubation at 37d̀C for 1 d. D and z values were determined. In both incubation procedures, better average recovery was obtained on blood agar than on TPA‐FE. Thus, higher D values were recorded when blood agar was used. In most cases the differences were statistically significant. Repair at 4d̀C of heat‐injured bacteria occurred on both media but the proportions of repaired bacteria were higher on blood agar. The repair on this medium was generally reflected in higher D values for preincubated samples. Some significant differences in heat resistance were noted between the strains.
Production and specificity of poly‐ and monoclonal antibodies raised against Shewanella putrefaciens
Authors: Fonnesbech Birte , Frøkiaer Hanne , Gram Lone , Jespersen C. Mosby
Published: March 2008

B. FONNESBECH, H. FRØKIAER, L. GRAM AND C. MOSBY JESPERSEN. 1993. Polyclonal antibodies were raised in rabbits and mice against Shewanella putrefaciens. Murine monoclonal antibodies were produced against the type strain (ATCC 8071) as well as wild type strains isolated from fish products. The specificities of four polyclonal and 12 monoclonal antibodies were tested by dot‐blotting, an indirect and a competitive ELISA against 16 Gram‐negative strains; including six strains of S. putrefaciens and one strain of Pseudomonas rubescens (NC 10695). All polyclonal antibodies reacted strongly with S. putrefaciens and with Ps. rubescens and cross‐reacted with the nine other bacteria (Pseudomonas spp., Aeromonas spp. and Vibrio anguillarum). The monoclonal antibodies could be divided into three groups with different patterns of specificity. The largest group (8 monoclonal antibodies) reacted strongly with S. putrefaciens and with Ps. rubescens and showed only weak reactions with the other strains. The results confirm that Ps. rubescens should be classified as S. putrefaciens.
Manipulation of Pseudomonas aeruginosa alginate pathway by varying the level of biosynthetic enzymes and growth temperature
Authors: Leitão J.H. , Sá‐Correia I.
Published: March 2008

J.H. LEITÃO AND i. SÁ‐CORREIA. 1993. The manipulation of the alginate pathway in two Pseudomonas aeruginosa mucoid variants was attempted at growth temperatures within the range 20d̀C‐40d̀C. This was carried out by increasing the level of either phosphomannose isomerase (PMI) and GDP‐mannose pyrophosphorylase (GMP) or GDP‐mannose dehydrogenase (GMD) encoded by algA or algD respectively, present in recombinant plasmids derived from the controlled expression vector pMMB24. The specific growth rate of cells expressing either algA or algD genes from recombinant plasmids was lower than that of cells harbouring the cloning vector only. Stimulation of alginate synthesis was observed when the expression of the alginate genes was low, in the absence of isopropyl‐β‐D‐thiogalactopyranoside (IPTG) induction. The further increase of the level of alginate enzymes in induced cells, without the simultaneous increase of other limiting steps, had no positive effect on the strictly regulated alginate pathway. Temperature profiles for alginate synthesis were modified reflecting changes in rate limiting steps. Limitations on the polymerization ability and the competition between cell growth and alginate synthesis were possibly involved in the modification of the temperature profiles for alginate production, or in the decrease of the molecular weight of polymers produced by recombinants under conditions that led to highly active alginate synthesis. The acetyl content of alginates produced by the recombinants was higher than that of the biopolymer controls, possibly due to the higher acetyl‐CoA availability in slower growing cells.
Phenotypic characteristics of the three hybridization groups of Aeromonas hydrophila complex isolated from different sources
Authors: HäUnninen Marja‐Liisa
Published: March 2008

Biochemical characteristics, SDS‐PAGE analysis of whole cell proteins and maximum growth temperature were used for phenotypic characterization of the three DNA hybridization groups (HG 1, HG 2 and HG 3) of the Aeromonas hydrophila complex (96 strains). DNA‐DNA hybridization was made with 22 strains using both 32P‐ and digoxigenin‐labelled probes. The strains originated from raw foods of animal origin, drinking water, fresh water, diseased fish and clinical material. The biochemical tests which were shown to be of value in the separation of the three hybridization groups (HG) were DL‐lactate and urocanic acid utilization and acid production from D‐sorbitol and from D‐rhamnose. A new marker, the maximum growth temperature determined with a temperature‐gradient incubator, was shown to separate HG 1 from HG 2 and HG 3. The mean maximum growth temperature (Tmax) of confirmed and putative HG 1 strains was significantly higher (41.1 ±0.56°C;P<0.001>)than that of HG 2 (38.2 ± 0.79°C) or HG 3 (38.6 ± 0.75°C) strains. The lower Tmax of HG 2 and HG 3 may explain why the results of biochemical tests may differ if incubation temperatures of 30° or 37°C are used. The SDS‐PAGE protein pattern analysis indicated that the strains of HG 3 have a band of variable molecular weight of 24, 25 or 26 kDa not possessed by strains of HG 1 and HG 2. HG 2 strains had two weak bands of molecular weight 24 and 25 kDa. HG 1 organisms were isolated from ground beef, chicken and clinical material but not from fresh water or drinking water. HG 2 and HG 3 organisms were isolated from foods of animal origin and from the water samples.
Microbiological evaluation of jejunal aspirates and faecal samples after oral administration of bifidobacteria and lactic acid bacteria
Authors: Nielsen O.H. , Jøorgensen S. , Pedersen K. , Justesen T.
Published: March 2008

A double‐blind placebo controlled investigation was carried out to study the effect of peroral colonization. Human volunteers were given mixtures of bifidobacteria and lactic acid bacteria. Measurements were made over a 1 week treatment period and for another week after the end of the treatment. Two different bacteriological preparations were used, one consisted of Enterococcus faecium and Bifidobacterium longum (a total of 6.4 times 108 cfu d‐1); the other consisted of Lactobacillus acidophilus, Bif. bifidum, Lact. delbrueckii ssp. bulgaricus, and Streptococcus thermophilus (a total of 9 times 109 cfu d‐1). Together with a placebo preparation, they were given to 24 healthy controls (eight in each group). Microbiological examinations of jejunal aspirates showed that viable counts of most species were below the detection limit. However, the test preparation containing Ent. faecium and Bif. longum significantly reduced the anaerobe: aerobe ratio in faeces by a factor of three during treatment (P= 0.03), and increased it by a factor of 30 during the following week (P<0.02>). This study shows that peroral administration of certain bacterial cultures may affect the distal intestinal microflora.
The use of Kluyveromyces fragilis for the extraction of orange peel pectins
Authors: Donaghy J.A. , McKay A.M.
Published: March 2008

Samples of orange peel were inoculated with the yeast Kluyveromyces fragilis and the yield and composition of the extracted pectin was monitored over a 3 d fermentation period. A maximum yield of 12.8% from dry albedo pulp was obtained after 24 h. The yield and the molecular weight distribution (measured by gel permeation) of the released pectins did not vary greatly over the 3 d process. Gas chromatography of the alditol acetates of the constituent monosaccharides present in the pectins showed that the highest rhamnosyl and galacturonide content coincided with maximum growth of the yeast. The glucose content of the pectins decreased throughout the extraction process.
Unmodified and recombinant strains of Lactobacillus plantarum are rapidly lost from the rumen by protozoal predation
Authors: Sharp R. , Hazlewood G.P. , Gilbert H.J. , O'Donnell A.G.
Published: March 2008

A genetically‐manipulated strain of Lactobacillus plantarum and the unmodified parent strain were introduced into the rumen of sheep at an initial inoculum level of 1 times 107 cfu ml‐1 of rumen fluid. There were no significant differences between the viable counts of the two inoculants throughout a 24 h sampling period. The rates of loss were 0.36 and 0.29 h‐1 (proportion of colony‐forming units lost, measured over the first 2 h) for the parent strain and recombinant strain respectively, and within 24 h of inoculation neither of the strains were detectable in rumen fluid. Further experiments in vitro revealed that the inoculants persisted in sterile rumen fluid with a loss rate of 0.044 and 0.057 h‐1 for the parent strain and the recombinant strain respectively. Incubations with rumen fluid alone, protozoa‐free rumen fluid and protozoa‐enriched rumen fluid revealed that protozoal predation was the most significant factor in the loss of the introduced population. The loss rates from protozoa‐free rumen fluid were not significantly different (P < 0.05) from those observed in sterile rumen fluid.
Antimicrobial activity of shredded carrot extracts on food‐borne bacteria and yeast
Authors: Babic I. , Nguyen‐the C. , Amiot M.J. , Aubert S.
Published: March 2008

Purified ethanolic extracts of peeled and shredded carrots showed an antimicrobial effect against a range of food‐borne micro‐organisms. The minimum inhibitory concentration, expressed as mg ml‐1 dried carrot material used for the extraction were: Leuconostoc mesenteroides, 27; Listeria monocytogenes, >27 <55; Staphylococcus aureus, >27 <55; Pseudomonas fluorescens, >55 <110; Candida lambica, >55 < 110; Escherichia coli, > 110 <220. The antimicrobial activity was not linked to phenolic compounds but was presumably due to apolar components. Free saturated fatty acid (dodecanoic acid) and methyl esters of saturated fatty acids (of dodecanoic and pentadecanoic acids) were identified in purified active extracts of carrots by gas chromatography coupled to mass spectrometry and could be responsible for the antimicrobial activity. This effect did not seem to play a role in the resistance of shredded carrots to microbial spoilage, although the antimicrobial activity was present in fresh carrots at concentrations sufficient to inhibit spoilage bacteria.
Storage of poultry meat under modified atmospheres or vacuum packs: possible role of microbial metabolites as indicator of spoilage
Authors: Kakouri Athanasia , Nychas G.J.E.
Published: March 2008

The effect of carbon dioxide (100%), nitrogen (100%), carbon dioxide/oxygen (20% : 80%) or vacuum pack at 3 and 10°C was studied on the microbial flora, in skinless poultry breast fillets or thigh meat. Lactic acid bacteria and Brochothrix thermosphacta were the predominant organisms in samples stored in vacuum packs, carbon dioxide and nitrogen. Pseudomonads grew only in oxygen/carbon dioxide packaging systems. The concentration of lactate diminished in both thigh and breast meat during storage at 3 and 10°C. This decrease was more pronounced in thigh meat stored under 20% : 80% carbon dioxide/oxygen. Acetate increased to varying degrees in all samples regardless of the storage conditions.
Comparative study of the frequency and flagellar serotype flora of Bacillus thuringiensis in soils and silkworm‐breeding environments
Authors: Ohba M. , Aratake Y.
Published: March 2008

Two environments, soils and silkworm (Bombyx mort)‐breeding farms, in Kumamoto Prefecture, Japan, were explored for the comparative analysis of the frequency and the flagellar (H) serotype flora of Bacillus thuringiensis. This organism was found in 39.3% of the sericulture farms and 18.5% of the silkworm litter samples. The frequency of B. thuringiensis was 4.5% among the populations of the Bacillus cereus/B. thuringiensis group in silkworm‐breeding insectaries. The predominant H serotype detected in silkworm litters was 4ac (35.6%), followed by serotypes 3abc (20.0%), 8ab (13.3%), 4ab (13.3%) and 7 (2.2%). The majority (87.1%) of sericulture‐derived isolates exhibited larvicidal activity against the silkworm and/or the mosquito, Aedes aegypti. Of soil samples examined, 8.1% contained B. thuringiensis. The frequency of B. thuringiensis colonies was 0.6% among soil populations of the B. cereus/B. thuringiensis group. Of 22 soil isolates, 14 were assigned to five H serotypes: 10, 17, 18, 21 and 29. Most soil isolates showed no insecticidal activity against B. mori and A. aegypti, but two, belonging to H serotype 10 and an undescribed serotype, exhibited moderate larvicidal activity against A. aegypti.
Biochemical and chemotaxonomic characterization of Pseudomonas stutzeri genomovars
Authors: Rosselló‐Mora R.A. , Lalucat J. , Dott W. , Kämpfer P.
Published: March 2008

A total of 48 strains representing the seven Pseudomonas stutzeri genomovars (DNA/DNA homology groups) were studied for cellular fatty acid composition, physiological characteristics and protein profiles. All strains were found to be homogeneous with respect to their fatty acid patterns. Numerical analysis of physiological properties demonstrated a considerable phenotypic heterogeneity within the genomovars. Characterization of the individual genomic groups on the basis of biochemical tests was not possible. In a numerical study of cellular protein patterns, two main clusters were obtained, one representing genomovars 1, 6 and 7 characterized by a high G + C content (mean value > 64 mol%), the other representing genomovars 2, 3, 4 and 5 with a low G + G content (< 64 mol%). The standardized cellular protein patterns have potential for differentiation of the genomic groupings within the species Ps. stutzeri as currently circumscribed.
Evaluation of a chromogenic chito‐oligosaccharide analogue, p‐nitrophenyl‐β‐D‐N,N'‐diacetylchitobiose, for the measurement of the chitinolytic activity of bacteria
Authors: Frändberg Emma , Schnürer J.
Published: March 2008

Three methods of quantifying chitinase activity were compared. The activities of crude chitinases of 10 bacterial isolates from different environments were estimated in terms of (1) the release of p‐nitrophenol from the chromogenic chito‐oligosaccharide analogues, p‐nitrophenyl‐β‐D‐N,N'‐diacetylchitobiose, p‐nitrophenyl‐N‐acetyl‐β‐D‐glucosamine and p‐nitrophenyl‐β‐D‐N,N',N″‐triacetylchitotriose, (2) the release of reducing sugars from chitin and (3) the formation of clearing zones on chitin agar. When crude chitinase from Bacillus pabuli was used the hydrolysis of p‐nitrophenyl‐β‐D‐N,N'‐diacetylchitobiose correlated well with the release of reducing sugars from chitin and the formation of clearing zones on chitin agar. However, when the activity of crude chitinases from the different bacterial isolates were compared no agreement was found between the hydrolysis of p‐nitrophenyl‐β‐D‐N,N'‐diacetylchitobiose and the release of reducing sugars from chitin or the formation of clearing zones on chitin agar. It was concluded that the assay with chromogenic p‐nitrophenyl chito‐oligosaccharide analogues is not well suited for studies that compare the chitinase activity of different bacteria.
Effect of some factors on determination of viable microbial cells by peroxyoxalate chemiluminescence method
Authors: Kon Oh Sang , Hee Cha Seung
Published: March 2008

The effects of physical and chemical factors on the production of H2O2 from Escherichia coli cells were studied. When 20 mmol 1‐1 Tris‐HCl buffer was used for this purpose the electron transport system (ETS) showed the highest activity at pH 7.6‐8.2. KCN promoted the production of H2O2 from E. coli cells, and the optimum concentration was changed in different reaction times and pH values. Glucose, 5 mg ml‐1, increased the ETS activity about twofold. The other substrates and surfactants did not increase the chemiluminescence intensity. NaNO2 and Na2SO4 in inorganic salts significantly reduced the ETS activity above 70%. In addition, the optimum temperature for the production of H2O2 was 30°C in this study. When glucose (5 mg ml‐1) and KCN (0.2 mmol 1‐1) were added to the reaction buffer containing 0.5 mmol 1‐1 menadione, the detectable minimum cell densities (averages of triplicate assay) of E. coli, Enterobacter cloacae and Serratia marcescens were 5 times 103 cells ml‐1, 104 cells ml‐1 and 104 cells ml‐1 respectively.
Inhibition of enterotoxigenic Escherichia coli by the microflora of the porcine ileum, in an in vitro semicontinuous culture system
Authors: Hillman K. , Murdoch Tracy A. , Spencer R.J. , Stewart C.S.
Published: March 2008

An in vitro fermentation system capable of maintaining at least part of the microbial population of the contents of the porcine ileum has been developed. The system was tested over the pH range 6.0‐8.5, anaerobically and at dissolved oxygen concentrations within the ranges detected in the ileum of piglets at weaning (50 and 100 μmol 1‐1). The results demonstrated that changes in pH and dissolved oxygen within these ranges had relatively little effect on the total numbers of aerobic and anaerobic bacteria. Lactic acid bacteria, enumerated anaerobically, showed changes in viable counts in response to pH changes but were apparently unaffected by changes in dissolved oxygen, although the proportion of aerotolerant species within this group was increased at high concentrations of dissolved oxygen. The relative proportions of lactobacilli and coliforms were similar to those reported in vivo when dissolved oxygen was present at a concentration of 50 μmol 1‐1. Under these conditions the simulated population was consistently found to resist colonization by an enterotoxigenic Escherichia coli, of a serotype known to cause weaning scours in the piglet.
Characterization of Iarvicidal toxin protein from Bacillus thuringiensis serovar japonensis strain Buibui specific for scarabaeid beetles
Authors: Hori H. , Suzuki N. , Ogiwara K. , Himejima M. , Indrasith L.S. , Minami M. , Asano S. , Sato R. , Ohba M. , Iwahana H.
Published: March 2008

The δ‐endo toxin proteins from Bacillus thuringiensis which kill the larvae of various scarabaeid beetles such as Anomala cuprea, A. rufocuprea and Popillia japonica were purified by DEAE ion exchange chromatography. A protein with a molecular size of 130 kDa was purified. During the purification a minor peak was also detected which was estimated to be 67 kDa by SDS‐PAGE. Both 130 and 67 kDa proteins showed larvicidal activity against A. cuprea. The lethal concentration of the 130 kDa protein which killed 50% of the larvae tested (LC50) against A. cuprea was 2 μg g1 compost. A comparison by SDS‐PAGE of the V8 protease digestion pattern of the 130 and 67 kDa larvicidal proteins showed that proteolytic resistant core peptides of approximately 60 kDa molecular size were resulted. The N‐terminus amino acid sequence of the 130 and 67 kDa proteins was determined to be NH2‐XXPNNQNEYEIIDAL and NH2‐XSRNPGTFI, respectively, which is not identical to the sequence of CryIA, CryIB, CryIC and CryIII proteins.
Tetracycline resistance genes in staphylococci from the skin of pigs
Authors: Schwarz S. , Noble W.C.
Published: March 2008

Forty‐seven tetracycline‐resistant staphylococci from the skin of pigs were examined for genes mediating this resistance. Seventeen isolates were also resistant to minocycline and all hybridized with the tet(M.) gene; 23 carried the tet(K) gene and 10 the tet(L) gene. Three carried more than one gene and two did not hybridize with any of the three probes tested. Maps were constructed for two plasmids carrying the tet(K) gene, all were very similar in size (4.35–4–7 kb) and structure and closely resembled the plasmid pT181. Four plasmids which bore the tet(L) gene differed in size, ranging from 4.3 to 11.5 kb, and were dissimilar in structure except for the portion bearing the gene.
Vitamin and amino acid requirements of Lactobacillus plantarum strains isolated from green olive fermentations
Authors: Ruiz‐Barba J.L. , Jiménez‐Díaz R.
Published: March 2008

The requirement for essential amino acids and vitamins was determined in wild‐type Lactobacillus plantarum strains isolated from green olive fermentation brines. All the strains were found to be auxotrophic with respect to the amino acids but some of them were prototrophic for pyridoxal, p‐aminobenzoic acid and/or nicotinic acid. Their growth response to these nutrients was also studied and found to be quite heterogeneous. Nutritional requirement pattern as a criteria for selecting starter cultures is discussed.
Thermal resistance of partially purified proteinase of Pseudomonas fluorescens P‐26
Authors: Uplacksh V.K. , Mathur D.K. , Malik R.K.
Published: March 2008

Heat resistance of thePseudomonas fluorescensP‐26 proteinase in terms ofD‐value was studied in whole milk, skim milk, whey and 0.05 mol 1‐1phosphate buffer at 72.5, 130, 135, 140, 145 and 150°C subsequent to its partial purification through (NH4)2SO4precipitation (45–65% saturation) and solvent fractionation with 1.0 to 2.0 volumes of isopropanol. TheD‐value was maximum for the proteinase at all temperatures when determined in whole milk (D150= 0.088).
Fermentation of fructans by epiphytic lactic acid bacteria
Authors: Müller Marina , Lier Dorothee
Published: March 2008

A total of 712 strains of lactic acid bacteria isolated from forage grasses were studied for their ability to ferment fructans of phlein‐ as well as inulin‐type. Only 16 strains utilized phlein and eight of these also fermented inulin. They were identified as Lactobacillus paracasei subsp. paracasei, Lact. plantarum, Lact. brevis and Pediococcus pentosaceus. In the species Lact. paracasei subsp. paracasei, all strains gave positive results, whereas the other positive strains possessed unique properties within their own species. In all but two cases (strains of the species Lact. plantarum), the phlein was more intensively fermented than the inulin, as indicated by a lower pH and a higher lactic acid concentration. On the basis of the outcome of this study it seems worthwhile to inoculate grasses of low sugar content before ensiling with an active strain that can ferment fructans.
The effect of electron beam irradiation and modified pH on the survival and recovery of Escherichia coli
Authors: Flelding L.M. , Cook P.E. , Grandison A.S.
Published: March 2008

The severity of radiation processing can be reduced by combining irradiation with other treatments, such as low pH. An exponential phase culture of Escherichia coli was irradiated at doses of 0–2.4 kGy at pH values ranging between 7.0 and 4.0, in an enriched nutrient broth.

At pH 4.3 and above there was no significant effect of lowering the pH prior to irradiation. At pH 4.13 and 4.0, a much higher level of cell death occurred compared with irradiation at pH 7.0. This synergistic effect was observed only when the pH was lowered before radiation processing.
A substrate‐mediated assay of bacterial proton efflux/influx to predict the degree of spoilage of beef mince stored at chill temperatures
Authors: Seymour I.J. , Cole M.B. , Coote P.J.
Published: March 2008

A method was developed to predict spoilage of minced meat at chill temperatures, based on the difference in proton efflux from and influx into bacterial cells. This difference depends on the number of organisms present, the available glucose in the meat sample and the ability of the organisms to metabolize amino acids. The proton efflux/influx of a meat filtrate containing bacteria was measured at 25°C with a pH/ion meter in the presence of peptone with or without glucose. There was a noticeable rate of change of mV h‐1 of the meat filtrate prior to the organoleptic detection of spoilage which may be used semi‐predictively to determine the remaining shelf‐life of meat at different storage temperatures. The method could be investigated further, encompassing type and relative numbers of organisms, incubation temperature, meat type and composition (i.e. available glucose) to produce a spoilage prediction model. The method does not require sophisticated equipment, only a standard pH/ion meter, is cheap, needing only peptone and glucose, is relatively simple, and takes less than 2 h to perform.
Factors that interact with the antibacterial action of thyme essential oil and its active constituents
Authors: Juven B.J. , Kanner J. , Schved F. , Weisslowicz H.
Published: March 2008

The viable counts of Salmonella typhimurium on nutrient agar (NA) decreased upon the addition of either the essential oil of thyme or its constituent thymol, especially under anaerobic conditions. Antagonistic effects of thymol against Staphylococcus aureus were also greater under anaerobic conditions. In contrast to the phenolic constituents of the oil, thymol and carvacrol, the chemically related terpenes p‐cymene and y‐terpinene had no antagonistic effects against Salm. typhimurium.

The addition of Desferal to NA counteracted the antibacterial effects of both thyme oil and thymol. No support was obtained, however, for a possible role of iron in the oxygen‐related antibacterial action of the thyme oil and thymol or for the observed effect of Desferal. In the presence of thymol, the viable counts of Salm. typhimurium obtained on a minimal medium (MM) were lower than those obtained on NA. Addition of bovine serum albumin (BSA) neutralized the antibacterial action of thymol. It is suggested that the effects of BSA or Desferal are due to their ability to bind phenolic compounds through their amino and hydroxylamine groups, respectively, thus preventing complexation reactions between the oil phenolic constituents and bacterial membrane proteins. This hypothesis is supported by the marked decrease in the viable counts of Salm. typhimurium caused by either thyme oil or thymol when the pH of the medium was changed from 6.5 to 5.5 or the concentration of Tween 80 in the medium was reduced.
Survival of genetically‐engineered and wild‐type strains of the yeast Saccharomyces cerevisiae under simulated environmental conditions: a contribution on risk assessment
Authors: Fujimura H. , Sakuma Y. , Amann E.
Published: March 2008

H. FUJIMURA, Y. SAKUMA AND E. AMANN. 1994. A genetically‐engineered strain of Saccharomyces cerevisiae employed for the industrial production of the human coagulation Factor XIIIa (rhFXIIIa) was used for a survival study under simulated environmental conditions. The homologous strain devoid of the recombinant plasmid and the homologous strain bearing the 2 μm‐based vector plasmid without the rhFXIIIa‐encoding DNA insert were compared. The strains were introduced into natural soil/water suspension, into soil/medium suspension and into waste water. After intervals, samples of cell suspensions were taken and viable cell numbers were determined by plating on antibiotic‐containing medium. In addition, a non‐radioactive technique involving enhanced chemiluminescence was employed to detect plasmid‐bearing yeast cells. The rhFXIIIa expression plasmid showed a high stability during the simulated environmental condition. No differences in survival rates, however, could be detected for the plasmid‐bearing and plasmid‐less strains under the three conditions tested, suggesting that the presence of plasmid does not confer selective advantages on the survival of the yeast cells. It is concluded that, even after accidental release of the engineered yeast cells into the environment, elimination rates would be comparable to those for non‐recombinant yeast strains.
Characterization of Aeromonas salmonicida subsp. salmonicida: a comparative study of strains of different geographic origin
Authors: Dalsgaard I. , Nielsen B. , Larsen J.L.
Published: March 2008

A total of 130 strains of the fish pathogen Aeromonas salmonicida isolated in Denmark, Norway, Scotland, Canada and the USA were examined. The strains originated from farmed salmonid fish. The biochemical, physiological and serological characteristics, antibiotic resistance patterns and cell surface‐related properties were compared. Aeromonas salmonicida was found to be remarkably consistent in general cultural and biochemical characteristics. It is noteworthy that the strains were positive in the fermentation of L‐arabinose and were negative in the fermentation of D‐arabinose. All the strains were highly proteolytic. It was observed, however, that 5% of the strains did not digest calf and trout serum and the production of haemolysin and degradation of casein by the same strains were delayed compared with the other strains. Common to all of the rough strains were auto‐aggregation and ability to bind the dyes Coomassie brilliant blue and Congo red and the majority of these strains were highly hydrophobic. The strains were tested for their susceptibility to 22 antibacterial agents. Antibiotic resistance profiles of Aer. salmonicida indicated that resistance to the quinolones and oxytetracycline was increasing and that multi‐resistant strains were found in several countries. The variation found in antibiograms could have potential as epidemiological markers in certain geographic areas.
Differential enumeration of silage inoculants based on utilization of enzymatic activity and antibiotic sensitivity of bacteria
Authors: Kneifel W. , Toros Arzu , Viernstein H.
Published: March 2008

A plate count method for the selective enumeration of silage inoculants is described. On the basis of a screening of lactic acid bacteria for various physiological criteria, enzyme profiles and antibiotic sensitivity, three MRS‐based agar media were developed. Pediococci but not lactobacilli and enterococci produced colonies on MRS agar containing ampicillin at 5 mg 1‐1, whereas only the enterococci grew on MRS agar containing clindamycin at the same level. On MRS‐X‐Gal agar with 50 μg ml‐1 5‐bromo‐4‐chloro‐3‐indolyl‐β‐D‐galactopyranoside (X‐Gal) and 1% (w/v) glucose lactobacilli colonies were blue‐coloured (because of their β‐D‐galactosidase activity) while all cocci gave white colonies. The performance of these media was demonstrated by examining two commonly applied silage culture preparations.
Growth rate and physiology of Yersinia enterocolitica; influence of temperature and presence of the virulence plasmid
Authors: Goverde Rosalina L. J. , Kusters J. G. , Huis in‘t Veld J. H. J.
Published: March 2008

The effect of temperature on the growth rate, protein pattern and fatty acid composition of Yersinia enterocolitica strain W22703 pYV+, its plasmidless isogenic derivative W22703 pYV‐ and four recent field isolates was examined.

The growth rate was clearly influenced by presence or absence of the virulence plasmid: pYV‐ strains grew consistently faster than pYV+ strains. This difference in growth rate was high at 30–35°C, moderate at 1–10°C and 25°C, but hardly significant at 15–20°C.

Increasing the growth temperature above 25°C resulted in the induction of the 220 kDa virulence plasmid‐encoded Yop1 protein. In the 1–20°C range no obvious temperature‐ or plasmid‐related differences in protein patterns could be detected.

The fatty acid composition showed a clear temperature‐dependent change: with all strains the degree of saturation was low at 1°C and gradually increased with raising temperatures. All strains had similar fatty acid patterns, except one of the field isolates which showed aberrant C16 : 1 and cyclic fatty acid contents in the 5–25°C and 15°C ranges respectively. With strain W22703, the presence or absence of the virulence plasmid did not significantly alter the fatty acid pattern.
Verification of ELISA results by immunomagnetic isolation of antigens from extracts and analysis with SDS‐PAGE and Western blotting, demonstrated for Erwinia spp. in potatoes
Authors: van der Wolf J.M. , van Beckhoven J.R.C.M. , de Vries Ph.M. , Vuurde J.W.L. van
Published: March 2008

Isolation of antigens on immunomagnetic beads and subsequent analysis with SDS‐PAGE and Western blotting (immunomagnetic isolation‐Western blotting (IMI‐WB)) was used to verify positive ELISA results for Erwinia chrysanthemi and Erw. carotovora subsp. atroseptica in potato peel extracts. Direct analysis of highly contaminated extracts by Western blotting without previous immuno‐isolation resulted in background reactions, whereas immunomagnetic isolation resulted in distinct bands of specific antigens. Target cells as well as antigenic cell products were captured in IMI‐WB. Band patterns on IMI‐WB of cell‐free culture filtrates and cell suspensions were highly similar, but the removal of cells lowered the detection level by 10‐ to 100‐fold. Threshold levels of IMI‐WB were generally comparable with those of ELISA.

No differences in threshold levels and band patterns were found between a direct format and an indirect format of immuno‐isolation.

In IMI‐WB, blotting patterns differed between Erw. chrysanthemi and Erw. carotovora subsp. atroseptica. The patterns were identical for 15 Erw. chrysanthemi strains, isolated from potato peel extracts in The Netherlands. However, one of 15 strains of Erw. carotovora subsp. atroseptica from potato peel extracts in The Netherlands gave an aberrant pattern. Target bacteria could be easily distinguished from those of cross‐reacting strains on the basis of band patterns.

Potato peel extracts naturally contaminated with Erw. chrysanthemi gave IMI‐WB patterns that were similar to pure cultures of the homologous strains.
An isoelectric focusing study of the effect of methyl‐esterified pectic substances on the production of extracellular pectin isoenzymes by soft rot Erwinia spp.
Authors: McMillan G.P. , Barrett A.M. , Pérombelon M.C.M.
Published: March 2008

The production of extracellular pectic isoenzymes by seven strains of soft rot bacteria, Erwinia carotovora subsp. carotovora, E.c. atroseptica and E. chrysanthemi, when grown in media containing four different pectic substances with different degrees of methylation or with potato tuber cell‐wall extract was examined by isoelectric focusing activity staining. In addition to the isoenzymes of pectate lyase, polygalacturonase and pectin methyl esterase produced constitutively or following induction by polygalacturonic acid (PGA) and coded by known genes, between two and seven novel isoenzymes of the three enzymes with a wider pI range were apparently induced by the pectins and cell‐wall extract. Pectin lyase, which is induced in vitro by DNA‐damaging agents, was not produced in the absence of mitomycin C in a medium containing PGA but up to two isoenzymes were found with pectin or cell‐wall extract. In contrast, cellulase isoenzyme production was not affected by pectin or cell‐wall extract. A greater number of novel isoenzymes of all pectic enzymes except pectin lyase tended to be produced in media containing Link pectin, which is PGA methylated to 98%, than the other pectic substances and cell‐wall extract. Pectate lyase and polygalacturonase were induced by pectin lyase‐degraded products of highly methylated pectin but not by PGA in an E. chrysanthemi strain with all its known pei and peh genes mutated. The results suggest that the production of novel pectic isoenzymes could be related to the presence of CH+3 groups and that their induction differs from that for isomers induced by PGA‐degraded products and DNA‐damaging agents or produced constitutively.