Incidence and identification of mesophilic Aeromonas spp. from retail foods

Sixty-eight food samples were examined for the presence of mesophilic Aeromonas species both qualitatively and quantitatively. Aeromonads were isolated from 26% of the vegetable samples, 70% of the meat and poultry samples and 72% of the fish and shrimps. Numbers of motile aeromonads present in the food samples varied from <10(2) cfu g(-1) to >10(5) cfu g(-1). GLC analysis of FAMEs was used to identify a selection of presumptive Aeromonas colonies to fenospecies or genomic species level. Aeromonas strains belonging to the Aer. caviae complex, which also includes the potentially pathogenic genospecies HG4, were mostly isolated from vegetables but were also found in meat, poultry and fish. In addition, three strains of the virulent taxon Aer. veronii biovar sobria HG8 were isolated from poultry and minced meat. All members of the Aer. hydrophila complex, predominant in the fish, meat and poultry samples, were classified in the non-virulent taxon HG3. Although the significance of Aeromonas in foods remains undefined, the isolation of Aeromonas HG4 and HG8 strains from a variety of retail foods may indicate that these products can act as possible vehicles for the dissemination of food-borne Aeromonas gastroenteritis.     

Characterization of oxytetracycline-resistant heterotrophic bacteria originating from hospital and freshwater fishfarm environments in England and Ireland

This ecotaxonomic study compared the antibiotic tolerance among culturable oxytetracyline-resistant (Ot(r)) heterotrophic strains isolated from two aquatic environments representing human activities in health care and aquaculture, namely hospital effluents and freshwater fishfarms. Using a standardized methodology, samples taken in England and Ireland were analyzed to determine the antibiotic tolerance profiles of two groups of culturable Ot(r) bacterial isolates at the intergeneric and intrageneric level comprising heterotrophs (189 strains) and mesophilic Aeromonas spp. (153 strains), respectively. Antibiogram data of heterotrophic isolates revealed that Irish hospital strains comprised higher frequencies of multi-tolerance than those originating from fishfarm environments whereas a reverse correlation was found among the English heterotrophs. Polyphasic identification of the isolates using fatty acid analysis and API 20E profiling showed that this difference arose from the unique taxonomic diversity within each heterotrophic strain set. Acinetobacter (27%) and Brevundimonas (22%) were predominant among the Irish Ot(r) fishfarm isolates, whereas isolates originating from the English aquaculture site almost entirely consisted of Stenotrophomonas maltophilia (86%) exhibiting high frequencies of tolerance to ampicillin and streptomycin. Within both the English and the Irish Ot(r) Aeromonas strain sets, on the other hand, the hospital strain sets displayed higher numbers of multi-tolerant isolates than to fishfarm isolates although country-specific differences were observed for individual antimicrobial agents. The typical occurrence of kanamycin-tolerant aeromonads in the Irish hospital site could to some extent be linked to the typical presence of A. hydrophila DNA hybridization group (HG) 3 strains as determined by fatty acid analysis and fluorescent amplified fragment length polymorphism (FAFLP) fingerprinting. Essentially, these data indicate that tolerance profiles in a specific environment of one country do not necessarily reflect the corresponding tolerance profiles of the same type of environment in another country, and this mainly as a result of the unique taxonomic composition of each site. Ot(r) representatives of Acinetobacter, S. maltophilia, and A. veronii biovar sobria HG8 were common to most if not all of the four sites under study, indicating that these three taxa may serve as potential indicator organisms for monitoring antibiotic tolerance among indigenous bacterial populations in various aquatic environments.     

Antipredator Benefits of Schooling Behaviour in a Cyprinodontid Fish,the Banded Killifish (Fundulus diaphanus)

Fish schools are believed to provide antipredator benefits to their members. Two potential antipredator benefits, the dilution and confusion effects, of schooling were investigated in the laboratory using banded killifish (Fundulus diaphanus). Individual risk of being attacked and killed by a fish predator (white perch, Morone americana) declined with increasing killifish school size in a manner closely predicted by the dilution hypothesis. Perch were apparently not confused by schooling killifish since fish in groups of one did not suffer a disproportionately greater predation rate than fish in all larger school sizes. However, killifish straggling from the school were preferentially attacked and more successfully captured compared with school members. Schooling in the banded killifish therefore confers a considerable antipredator benefit to individual group members, at least through a dilution effect, and straying from a school has an associated increased risk of mortality to predation, which selects for schooling behaviour.     

Automated assay for screening the enzymatic release of reducing sugars from micronized biomass

Background  

To reduce the production cost of bioethanol obtained from fermentation of the sugars provided by degradation of lignocellulosic biomass (i.e., second generation bioethanol), it is necessary to screen for new enzymes endowed with more efficient biomass degrading properties. This demands the set-up of high-throughput screening methods. Several methods have been devised all using microplates in the industrial SBS format. Although this size reduction and standardization has greatly improved the screening process, the published methods comprise one or more manual steps that seriously decrease throughput. Therefore, we worked to devise a screening method devoid of any manual steps.     

Identification of lactobacilli isolated from the cloaca and vagina of laying hens and characterization for potential use as probiotics to control Salmonella Enteritidis

AIMS: To select Lactobacillus strains from laying hens for potential use as probiotic to control Salmonella Enteritidis infection. METHODS AND RESULTS: One hundred and eighty-six lactobacilli were isolated from the cloaca and vagina of laying hens, and identified at the species level by a polyphasic taxonomic approach. All isolates belonged to the Lactobacillus acidophilus, Lactobacillus reuteri or Lactobacillus salivarius phylogenetic groups, with the L. reuteri group being the most predominant group. Based on genetic diversity, about 50 representative strains were selected and tested for in vitro properties that could be predictive for probiotic activity in laying hens. Salmonella inhibition was shown to be species dependent, and correlated to some extent with the production of lactic acid. A selection of strains was evaluated in a S. Enteritidis challenge experiment. Two strains, L. reuteri R-17485 and Lactobacillus johnsonii R-17504 significantly decreased the colonization of chicks by S. Enteritidis in caeca, liver and spleen. CONCLUSIONS: Lactobacilli isolated from laying hens were observed to inhibit Salmonella growth in vitro, most probably through production of lactic acid, and to decrease in vivo the S. Enteritidis colonization of chicks. SIGNIFICANCE AND IMPACT OF THE STUDY: The data demonstrate that Lactobacillus isolates from laying hens may have probiotic potential in reducing S. Enteritidis infection.     

Biodiversity of lactic acid bacteria in Moroccan soft white cheese (Jben)

The bacterial diversity occurring in traditional Moroccan soft white cheese, produced in eight different regions in Morocco, was studied. A total of 164 lactic acid bacteria were isolated, purified and identified by whole-cell protein fingerprinting and rep-PCR genomic fingerprinting. The majority of the strains belonged to the genera Lactobacillus, Lactococcus, Leuconostoc and Enterococcus. Sixteen species were identified: Lactobacillus plantarum, Lactobacillus rhamnosus, Lactobacillus paracasei, Lactobacillus brevis, Lactobacillus buchneri, Lactococcus lactis, Lactococcus garvieae, Lactococcus raffinolactis, Leuconostoc pseudomesenteroides, Leuconostoc mesenteroides, Leuconostoc citreum, Eterococcus durans, Enterococcus faecalis, Enterococcus faecium, Enterococcus saccharominimus and Streptococcus sp.     

Mining fatty acid databases for detection of novel compounds in aerobic bacteria

This study examines how the discriminatory power of an automated bacterial whole-cell fatty acid identification system can be significantly enhanced by exploring the vast amounts of information accumulated during 15 years of routine gas chromatographic analysis of the fatty acid content of aerobic bacteria. Construction of a global peak occurrence histogram based upon a large fatty acid database is shown to serve as a highly informative tool for assessing the delineation of the naming windows used during the automatic recognition of fatty acid compounds. Along the lines of this data mining application, it is suggested that several naming windows of the Sherlock MIS TSBA50 peak naming method may need to be re-evaluated in order to fit more closely with the bulk of observed fatty acid profiles. At the same time, the global peak occurrence histogram has put forward the delineation of 32 new peak naming windows, accounting for a 26% increase in the total number of fatty acid features taken into account for bacterial identification. By scrutinizing the relationships between the newly delineated naming windows and the many taxonomic units covered within a proprietary fatty acid database, all new naming windows were proven to correspond with stable features of some specific groups of microorganisms. This latter analysis clearly underscores the impact of incorporating the new fatty acid compounds for improving the resolution of the bacterial identification system and endorses the applicability of knowledge discovery in databases within the field of microbiology.