bluuebunny/crossref_metadata_2025_split huggingface dataset:
Competitive Exclusion of
Salmonella enterica
serovar Enteritidis by
Lactobacillus crispatus
and
Clostridium lactatifermentans
in a Sequencing Fed-Batch Culture
Authors: van der Wielen Paul W. J. J. , Lipman Len J. A. , van Knapen Frans , Biesterveld Steef 
Published: February 2003

ABSTRACT

Competitive exclusion of
Salmonella enterica
serovar Enteritidis by a mixed culture of
Lactobacillus crispatus
and
Clostridium lactatifermentans
was studied in a sequencing fed-batch reactor mimicking the cecal ecophysiology of broiler chickens. Growth of serovar Enteritidis was inhibited by a mixed culture of
L. crispatus
and
C. lactatifermentans
at pH 5.8 but not by a monoculture of
L. crispatus
at the same pH. Moreover, experiments performed at pH 7.0 did not show growth inhibition of serovar Enteritidis.
L. crispatus
fermented lactose to lactate, and
C. lactatifermentans
fermented the lactate to acetate and propionate in a mixed culture of
L. crispatus
and
C. lactatifermentans
growing on lactose. In contrast, only lactate was produced from lactose by a monoculture of
L. crispatus
. At pH 5.8 considerable concentrations of acetate and propionate were present as undissociated acids, whereas only trace levels of undissociated lactate were present at pH 5.8 due to the low pK
a
of lactate. At pH 7.0 all three acids were present in their dissociated forms. We conclude that a mixed culture of
L. crispatus
and
C. lactatifermentans
inhibits growth of serovar Enteritidis under cecal growth conditions. The undissociated forms of acetate and propionate produced in the mixed culture inhibited the growth of serovar Enteritidis.
Antimicrobial Resistance of
Escherichia coli
O157 Isolated from Humans, Cattle, Swine, and Food
Authors: Schroeder Carl M. , Zhao Cuiwei , DebRoy Chitrita , Torcolini Jocelyn , Zhao Shaohua , White David G. , Wagner David D. , McDermott Patrick F. , Walker Robert D. , Meng Jianghong 
Published: February 2003

ABSTRACT

A total of 361
Escherichia coli
O157 isolates, recovered from humans, cattle, swine, and food during the years 1985 to 2000, were examined to better understand the prevalence of antimicrobial resistance among these organisms. Based on broth microdilution results, 220 (61%) of the isolates were susceptible to all 13 antimicrobials tested. Ninety-nine (27%) of the isolates, however, were resistant to tetracycline, 93 (26%) were resistant to sulfamethoxazole, 61 (17%) were resistant to cephalothin, and 48 (13%) were resistant to ampicillin. Highest frequencies of resistance occurred among swine isolates (
n
= 70), where 52 (74%) were resistant to sulfamethoxazole, 50 (71%) were resistant to tetracycline, 38 (54%) were resistant to cephalothin, and 17 (24%) were resistant to ampicillin. Based on the presence of Shiga toxin genes as determined by PCR, 210 (58%) of the isolates were identified as Shiga toxin-producing
E. coli
(STEC). Among these, resistance was generally low, yet 21 (10%) were resistant to sulfamethoxazole and 19 (9%) were resistant to tetracycline. Based on latex agglutination, 189 (52%) of the isolates were identified as
E. coli
O157:H7, among which 19 (10%) were resistant to sulfamethoxazole and 16 (8%) were resistant to tetracycline. The data suggest that selection pressure imposed by the use of tetracycline derivatives, sulfa drugs, cephalosporins, and penicillins, whether therapeutically in human and veterinary medicine or as prophylaxis in the animal production environment, is a key driving force in the selection of antimicrobial resistance in STEC and non-STEC O157.
Expression of Antisense RNA Targeted against
Streptococcus thermophilus
Bacteriophages
Authors: Sturino Joseph M. , Klaenhammer Todd R. 
Published: February 2003

ABSTRACT

Antisense RNA complementary to a putative helicase gene (
hel3.1
) of a
cos
-type
Streptococcus thermophilus
bacteriophage was used to impede the proliferation of a number of
cos
-type
S. thermophilus
bacteriophages and one
pac
-type bacteriophage. The putative helicase gene is a component of the Sfi21-type DNA replication module, which is found in a majority of the
S. thermophilus
bacteriophages of industrial importance. All bacteriophages that strongly hybridized a 689-bp internal
hel3.1
probe were sensitive to the expression of antisense
hel3.1
RNA. A 40 to 70% reduction in efficiency of plaquing (EOP) was consistently observed, with a concomitant decrease in plaque size relative to that of the
S. thermophilus
parental strain. When progeny were released, the burst size was reduced. Growth curves of
S. thermophilus
NCK1125, in the presence of variable levels of bacteriophage κ3, showed that antisense
hel3.1
conferred protection, even at a multiplicity of infection of approximately 1.0. When the
hel3.1
antisense RNA cassette was expressed in
cis
from the κ3-derived phage-encoded resistance (PER) plasmid pTRK690::
ori3.1
, the EOP for bacteriophages sensitive to PER and antisense targeting was reduced to between 10
−7
and 10
−8
, beyond the resistance conferred by the PER element alone (less than 10
−6
). These results illustrate the first successful applications of antisense RNA and explosive delivery of antisense RNA to inhibit the proliferation of
S. thermophilus
bacteriophages.
Novel Fungitoxicity Assays for Inhibition of Germination-Associated Adhesion of
Botrytis cinerea
and
Puccinia recondita
Spores
Authors: Slawecki Richard A. , Ryan Eileen P. , Young David H. 
Published: February 2003

ABSTRACT

Botrytis cinerea
and
Puccinia recondita
spores adhere strongly to polystyrene microtiter plates coincident with germination. We developed assays for inhibition of spore adhesion in 96-well microtiter plates by using sulforhodamine B staining to quantify the adherent spores. In both organisms, fungicides that inhibited germination strongly inhibited spore adhesion, with 50% effective concentrations (EC
50
s) comparable to those for inhibition of germination. In contrast, fungicides that acted after germination in
B. cinerea
inhibited spore adhesion to microtiter plates only at concentrations much higher than their EC
50
s for inhibition of mycelial growth. Similarly, in
P. recondita
the ergosterol biosynthesis inhibitors myclobutanil and fenbuconazole acted after germination and did not inhibit spore adhesion. The assays provide a rapid, high-throughput alternative to traditional spore germination assays and may be applicable to other fungi.
Effect of Commercial-Scale High-Temperature, Short-Time Pasteurization on the Viability ofMycobacterium paratuberculosisin Naturally Infected Cows' Milk
Authors: Grant Irene R. , Hitchings Edward I. , McCartney Alan , Ferguson Fiona , Rowe Michael T. 
Published: February 2003

ABSTRACTRaw cows' milk naturally infected withMycobacterium paratuberculosiswas pasteurized with an APV HXP commercial-scale pasteurizer (capacity 2,000 liters/h) on 12 separate occasions. On each processing occasion, milk was subjected to four different pasteurization treatments, viz., 73°C for 15 s or 25 s with and without prior homogenization (2,500 lb/in2in two stages), in an APV Manton Gaulin KF6 homogenizer. Raw and pasteurized milk samples were tested forM. paratuberculosisby immunomagnetic separation (IMS)-PCR (to detect the presence of bacteria) and culture after decontamination with 0.75% (wt/vol) cetylpyridinium chloride for 5 h (to confirm bacterial viability). On 10 of the 12 processing occasions,M. paratuberculosiswas detectable by IMS-PCR, culture, or both in either raw or pasteurized milk. Overall, viableM. paratuberculosiswas cultured from 4 (6.7%) of 60 raw and 10 (6.9%) of 144 pasteurized milk samples. On one processing day, in particular,M. paratuberculosisappeared to have been present in greater abundance in the source raw milk (evidenced by more culture positives and stronger PCR signals), and on this occasion, survivingM. paratuberculosisbacteria were isolated from milk processed by all four heat treatments, i.e., 73°C for 15 and 25 s with and without prior homogenization. On one other occasion, survivingM. paratuberculosisbacteria were isolated from an unhomogenized milk sample that had been heat treated at 73°C for 25 s. Results suggested that homogenization increases the lethality of subsequent heat treatment to some extent with respect toM. paratuberculosis, but the extended 25-s holding time at 73°C was found to be no more effective at killingM. paratuberculosisthan the standard 15-s holding time. This study provides clear evidence thatM. paratuberculosisbacteria in naturally infected milk are capable of surviving commercial high-temperature, short-time pasteurization if they are present in raw milk in sufficient numbers.
Conversion of
l
-Leucine to Isovaleric Acid by
Propionibacterium freudenreichii
TL 34 and ITGP23
Authors: Thierry Anne , Maillard Marie-Bernadette , Yvon Mireille 
Published: February 2003

ABSTRACT

Several branched-chain volatile compounds are involved in the flavor of Swiss cheese. These compounds are probably produced by enzymatic conversion of branched-chain amino acids, but the flora and the pathways involved remain hypothetical. Our aim was to determine the ability of
Propionibacterium freudenreichii
, which is one of the main components of the secondary flora of Swiss cheese, to produce flavor compounds during leucine catabolism. Cell extracts and resting cells of two strains were incubated in the presence of
l
-leucine, α-ketoglutaric acid, and cofactors, and the metabolites produced were determined by high-performance liquid chromatography and gas chromatography. The first step of leucine catabolism was a transamination that produced α-ketoisocaproic acid, which was enzymatically converted to isovaleric acid. Both reactions were faster at pH 8.0 than at acidic pHs. Cell extracts catalyzed only the transamination step under our experimental conditions. Small amounts of 3-methylbutanol were also produced by resting cells, but neither 3-methylbutanal norα-hydroxyisocaproic acid was detected.
l
-Isoleucine and
l
-valine were also converted to the corresponding acids and alcohols. Isovaleric acid was produced by both strains during growth in a complex medium, even under conditions simulating Swiss cheese conditions (2.1% NaCl, pH 5.4, 24°C). Our results show that
P. frendenreichii
could play a significant role in the formation of isovaleric acid during ripening.
Characterization ofWolbachiaHost Cell Range via the In Vitro Establishment of Infections
Authors: Dobson Stephen L. , Marsland Eric J. , Veneti Zoe , Bourtzis Kostas , O'Neill Scott L. 
Published: February 2003

ABSTRACTMaternally transmitted bacteria of the genusWolbachiaare obligate, intracellular symbionts that are frequently found in insects and cause a diverse array of reproductive manipulations, including cytoplasmic incompatibility, male killing, parthenogenesis, and feminization. Despite the existence of a broad range of scientific interest, many aspects ofWolbachiaresearch have been limited to laboratories with insect-rearing facilities. The inability to culture these bacteria outside of the invertebrate host has also led to the existing bias ofWolbachiaresearch toward infections that occur in host insects that are easily reared. Here, we demonstrate thatWolbachiainfections can be simply established, stably maintained, and cryogenically stored in vitro using standard tissue culture techniques. We have examinedWolbachiahost range by introducing differentWolbachiatypes into a single tissue culture. The results show that anAedes albopictus(Diptera: Culicidae) cell line can support five differentWolbachiainfection types derived fromDrosophila simulans(Diptera: Drosophilidae),Culex pipiens(Culicidae), andCadra cautella(Lepidoptera: Phycitidae). These bacterial types include infection types that have been assigned to two of the majorWolbachiaclades. As an additional examination ofWolbachiahost cell range, we demonstrated that aWolbachiastrain fromD. simulanscould be established in host insect cell lines derived fromA. albopictus,Spodoptera frugiperda(Lepidoptera: Noctuidae), andDrosophila melanogaster. These results will facilitate the development of aWolbachiastock center, permitting novel approaches for the study ofWolbachiainfections and encouragingWolbachiaresearch in additional laboratories.
Culture-Independent Analysis of Gut Bacteria: the Pig Gastrointestinal Tract Microbiota Revisited
Authors: Leser Thomas D. , Amenuvor Joanna Z. , Jensen Tim K. , Lindecrona Rikke H. , Boye Mette , Møller Kristian 
Published: February 2003

ABSTRACT

The phylogenetic diversity of the intestinal bacterial community in pigs was studied by comparative 16S ribosomal DNA (rDNA) sequence analysis. Samples were collected from a total of 24 pigs representing a variety of diets, ages, and herd health status. A library comprising 4,270 cloned 16S rDNA sequences obtained directly by PCR from 52 samples of either the ileum, the cecum, or the colon was constructed. In total, 375 phylotypes were identified using a 97% similarity criterion. Three hundred nine of the phylotypes (83%) had a <97% sequence similarity to any sequences in the database and may represent yet-uncharacterized bacterial genera or species. The phylotypes were affiliated with 13 major phylogenetic lineages. Three hundred four phylotypes (81%) belonged to the low-G+C gram-positive division, and 42 phylotypes (11.2%) were affiliated with the
Bacteroides
and
Prevotella
group. Four clusters of phylotypes branching off deeply within the low-G+C gram-positive bacteria and one in the
Mycoplasma
without any cultured representatives were found. The coverage of all the samples was 97.2%. The relative abundance of the clones approximated a lognormal distribution; however, the phylotypes detected and their abundance varied between two libraries from the same sample. The results document that the intestinal microbial community is very complex and that the majority of the bacterial species colonizing the gastrointestinal tract in pigs have not been characterized.
Chemostat Approach for the Directed Evolution of Biodesulfurization Gain-of-Function Mutants
Authors: Arensdorf Joseph J. , Loomis A. Katrina , DiGrazia Philip M. , Monticello Daniel J. , Pienkos Philip T. 
Published: February 2003

ABSTRACT

Chemostat enrichment is a classical microbiological method that is well suited for use in directed-evolution strategies. We used a two-phase sulfur-limited chemostat to select for gain-of-function mutants with mutations in the biodesulfurization (Dsz) system of
Rhodococcus erythropolis
IGTS8, enriching for growth in the presence of organosulfur compounds that could not support growth of the wild-type strain. Mutations arose that allowed growth with octyl sulfide and 5-methylbenzothiophene as sole sulfur sources. An isolate from the evolved chemostat population was genetically characterized and found to contain mutations in two genes,
dszA
and
dszC
. A transversion (G to T) in
dszC
codon 261 resulted in a V261F mutation that was determined to be responsible for the 5-methylbenzothiophene gain-of-function phenotype. By using a modified RACHITT (random chimeragenesis on transient templates) method, mutant DszC proteins containing all possible amino acids at that position were generated, and this mutant set was assayed for the ability to metabolize 5-methylbenzothiophene, alkyl thiophenes, and dibenzothiophene. No mutant with further improvements in these catalytic activities was identified, but several clones lost all activity, confirming the importance of codon 261 for enzyme activity.
16S Ribosomal DNA-Based Analysis of Bacterial Diversity in Purified Water Used in Pharmaceutical Manufacturing Processes by PCR and Denaturing Gradient Gel Electrophoresis
Authors: Kawai Mako , Matsutera Eiichi , Kanda Hisashi , Yamaguchi Nobuyasu , Tani Katsuji , Nasu Masao 
Published: February 2003

ABSTRACT

The bacterial community in partially purified water, which is prepared by ion exchange from tap water and is used in pharmaceutical manufacturing processes, was analyzed by denaturing gradient gel electrophoresis (DGGE). 16S ribosomal DNA fragments, including V6, -7, and -8 regions, were amplified with universal primers and analyzed by DGGE. The bacterial diversity in purified water determined by PCR-DGGE banding patterns was significantly lower than that of other aquatic environments. The bacterial populations with esterase activity sorted by flow cytometry and isolated on soybean casein digest (SCD) and R2A media were also analyzed by DGGE. The dominant bacterium in purified water possessed esterase activity but could not be detected on SCD or R2A media. DNA sequence analysis of the main bands on the DGGE gel revealed that culturable bacteria on these media were
Bradyrhizobium
sp.,
Xanthomonas
sp., and
Stenotrophomonas
sp., while the dominant bacterium was not closely related to previously characterized bacteria. These data suggest the importance of culture-independent methods of quality control for pharmaceutical water.
Listeria monocytogenes
LO28: Surface Physicochemical Properties and Ability To Form Biofilms at Different Temperatures and Growth Phases
Authors: Chavant Patrick , Martinie Brigitte , Meylheuc Thierry , Bellon-Fontaine Marie-Noëlle , Hebraud Michel 
Published: February 2003

ABSTRACT

The surface physicochemical properties of
Listeria monocytogenes
LO28 under different conditions (temperature and growth phase) were determined by use of microelectrophoresis and microbial adhesion to solvents. The effect of these parameters on adhesion and biofilm formation by
L. monocytogenes
LO28 on hydrophilic (stainless steel) and hydrophobic (polytetrafluoroethylene [PTFE]) surfaces was assessed. The bacterial cells were always negatively charged and possessed hydrophilic surface properties, which were negatively correlated with growth temperature. The colonization of the two surfaces, monitored by scanning electron microscopy, epifluorescence microscopy, and cell enumeration, showed that the strain had a great capacity to colonize both surfaces whatever the incubation temperature. However, biofilm formation was faster on the hydrophilic substratum. After 5 days at 37 or 20°C, the biofilm structure was composed of aggregates with a three-dimensional shape, but significant detachment took place on PTFE at 37°C. At 8°C, only a bacterial monolayer was visible on stainless steel, while no growth was observed on PTFE. The growth phase of bacteria used to inoculate surfaces had a significant effect only in some cases during the first steps of biofilm formation. The surface physicochemical properties of the strain are correlated with adhesion and surface colonization.
Horizontal Transfer of the Plant Virulence Gene,
nec1
, and Flanking Sequences among Genetically Distinct
Streptomyces
Strains in the Diastatochromogenes Cluster
Authors: Bukhalid R. A. , Takeuchi T. , Labeda D. , Loria R. 
Published: February 2003

ABSTRACT

Evidence for the horizontal transfer of a pathogenicity island (PAI) carrying the virulence gene
nec1
and flanking sequences among
Streptomyces
strains in the Diastatochromogenes cluster is presented. Plant-pathogenic, thaxtomin-producing
Streptomyces
strains, previously classified as
S. scabiei
based on the conventionally used phenotypic characteristics, were found to be genetically distinct from the type strain of
S. scabiei
based on DNA relatedness and 16S rDNA sequence analysis. Pairwise DNA-DNA hybridizations between some of these strains and the
S. scabiei
type strain were as low as 36%, a value much below what is conventionally accepted for species identity (70%). The sequence of the
nec1
gene, however, was identical in all the
S. scabiei
and
S. scabiei
-like strains tested, irrespective of their DNA relatedness to the type strain of
S. scabiei
, their geographic origin, or the isolation host. Furthermore, a 26-kb DNA fragment including and flanking
nec1
was also conserved among these strains based on restriction and Southern analyses. These data indicate that the etiology of potato scab is more complex than previously recognized; this result has important implications for potato scab management strategies. Previous research has suggested that horizontal transfer of a PAI was the mechanism for evolution of pathogenicity in
S. acidiscabies
and
S. turgidiscabies
, species that lie outside of the Diastatochromogenes cluster. Data presented here support this model and indicate that PAI transfer also has occurred frequently in species closely related to
S. scabiei
.
Molecular Analyses of the Natural Transformation Machinery and Identification of Pilus Structures in the Extremely Thermophilic Bacterium
Thermus thermophilus
Strain HB27
Authors: Friedrich Alexandra , Prust Christina , Hartsch Thomas , Henne Anke , Averhoff Beate 
Published: February 2003

ABSTRACT

Thermus thermophilus
HB27, an extremely thermophilic bacterium, exhibits high competence for natural transformation. To identify genes of the natural transformation machinery of
T. thermophilus
HB27, we performed homology searches in the partially completed
T. thermophilus
genomic sequence for conserved competence genes. These analyses resulted in the detection of 28 open reading frames (ORFs) exhibiting significant similarities to known competence proteins of gram-negative and gram-positive bacteria. Disruption of 15 selected potential competence genes led to the identification of 8 noncompetent mutants and one transformation-deficient mutant with a 100-fold reduced transformation frequency. One competence protein is similar to DprA of
Haemophilus influenzae
, seven are similar to type IV pilus proteins of
Pseudomonas aeruginosa
or
Neisseria gonorrhoeae
(PilM, PilN, PilO, PilQ, PilF, PilC, PilD), and another deduced protein (PilW) is similar to a protein of unknown function in
Deinococcus radiodurans
R1. Analysis of the piliation phenotype of
T. thermophilus
HB27 revealed the presence of single pilus structures on the surface of the wild-type cells, whereas the noncompetent
pil
mutants of
Thermus
, with the exception of the
pilF
mutant, were devoid of pilus structures. These results suggest that pili and natural transformation in
T. thermophilus
HB27 are functionally linked.