Molecular diversity and characterization of tetracycline-resistant Staphylococcus aureus isolates from a poultry processing plant.

DNA fingerprinting and molecular characterization showed that the tetracycline-resistant Staphylococcus aureus population of a South African poultry processing plant comprised one or possibly several tet(K)-containing endemic clones that contaminated chicken and machinery surfaces at all sampled processing stages. The tet(K) gene was transferable by filter mating to S. aureus recipient 80CR5 and was located on a pT181-like plasmid.

Bacterial Populations Associated with the Processing of Cape Hake ( Merluccius capensis and Merluccius paradoxus ).

Numbers of bacteria associated with Cape hake from catching through processing to the finished product and final spoilage were determined by pour plating on Sea Water Agar (SWA). Subsequently, a total of 1,020 predominant bacteria from the different stages were isolated and identified to genus level. A significant reduction (p<0.05) in bacterial numbers after the first wash during processing ashore and a significant increase (p<0.05) after day 3 of refrigerated storage of final product were observed. No significant differences in bacterial numbers between the different stages onboard the trawler or during processing ashore were apparent. Psychrotrophic bacteria from predominantly four genera, namely Moraxella , Pseudomonas , Corynebacterium and Micrococcus , were isolated in this study. The relative proportions of these organisms was found to change only to a small extent during the chilled processing chain, with the genus Moraxella (46 to 57%) predominating. After several days of refrigerated storage, however, the relative proportion of Pseudomonas increased (from 34 to 90%) leaving this genus predominating in spoiled product.

Bacterial Populations of Different Sample Types from Carcasses in the Dirty Area of a South African Poultry Abattoir.

Bacterial populations associated with three different sample types from carcasses in the dirty area of a South African poultry abattoir were compared. The three sample types from carcasses before and after scalding included neck skin only, feathers only, and a neck skin and feather combination. The neck skin of carcasses after defeathering was also sampled. Aerobic plate counts, Enterobacteriaceae counts, and Pseudomonas spp. counts were performed on all sample types, as well as on water, air, and equipment samples from the same area. The prevalence of potential pathogens was also investigated. Neck skins sampled before and after scalding consistently exhibited the lowest counts for all bacterial types, and feathers the highest. In most cases, the bacterial numbers of the neck skin samples from pre- and postscalded carcasses were significantly lower (P < 0.05) than those of feather samples and neck skin and feather combination samples. Scalding of carcasses resulted in a consistent decrease of bacterial populations, reflected by all three sample types. Neck skins sampled after defeathering, however, exhibited increased bacterial numbers compared to neck skins sampled postscalding, implicating the rubber fingers of the defeathering machine as contamination sources. These equipment surfaces exhibited aerobic plate counts as high as 7.7 log CFU/cm2. Potential pathogens were isolated from product as well as selected environmental samples. The prevalence of the potential pathogens was found to vary depending on the sample type.

Proteomic analysis reveals differential protein expression by Bacillus cereus during biofilm formation.

Bacillus cereus, a dairy-associated toxigenic bacterium, readily forms biofilms on various surfaces and was used to gain a better understanding of biofilm development by gram-positive aerobic rods. B. cereus DL5 was shown to readily adapt to an attached mode of growth, with dense biofilm structures developing within 18 h after inoculation when glass wool was used as a surface. Two-dimensional gel electrophoresis (2DE) revealed distinct and reproducible phenotypic differences between 2- and 18-h-old biofilm and planktonic cells (grown both in the presence and in the absence of glass wool). Whereas the 2-h-old biofilm proteome indicated expression of 15 unique proteins, the 18-h-old biofilm proteome contained 7 uniquely expressed proteins. Differences between the microcolony (2-h) proteome and the more developed biofilm (18-h) proteome were largely due to up- and down-regulation of the expression of a multitude of proteins. Selected protein spots excised from 2DE gels were subjected to N-terminal sequencing and identified with high confidence. Among the proteins were catabolic ornithine carbamoyltransferase and L-lactate dehydrogenase. Interestingly, increased levels of YhbH, a member of the sigma 54 modulation protein family which is strongly induced in response to environmental stresses and energy depletion via both sigma(B) and sigma(H), could be observed within 2 h in both attached cells and planktonic cultures growing in the presence of glass wool, indicating that this protein plays an important role in regulation of the biofilm phenotype. Distinct band differences were also found between the extracellular proteins of 18-h-old cultures grown in the presence and in the absence of glass wool.

Sequence and structural relationships of leucocins A-, B- and C-TA33a from Leuconostoc mesenteroides TA33a.

Amino acid sequences of two of the three bacteriocins from Leuconostoc mesenteroides TA33a were determined and their sequence-structure relationships investigated. Leucocin B-TA33a consists of 31 amino acid residues, with a molecular mass of 3466 Da. Leucocin B-TA33a does not belong to the pediocin family of bacteriocins, but shares 62% homology with mesenterocin 52B. A partial sequence of 36 amino acids of leucocin C-TA33a (4598 Da) was determined. Leucocin C-TA33a belongs to the class II bacteriocins having the consensus YGNGV motif. The third bacteriocin, leucocin A-TA33a, is identical to leucocin A-UAL 187. Circular dichroism spectra of the leucocins in aqueous solution and micellar SDS indicated that they undergo a structural transition when in a membrane-mimicking environment. Theoretical predictions from circular dichroism data suggest that leucocins A-, B- and C-TA33a adopt a beta-structure (48%) in membrane-mimicking environments. Sequence alignments and secondary structure predictions for the N-terminus of leucocins A- and C-TA33a predicted that Cys-9 and Cys-14 are connected by a disulfide bridge and form two beta-strands.