Decarboxylase activity involved in methyl ketone production by Staphylococcus carnosus 833, a strain used in sausage fermentation.

Staphylococcus carnosus strain 833, inoculated into sausage, increased the levels of methyl ketones which contributed to the cured aroma. These ketones were predicted to arise from incomplete beta-oxidation followed by a decarboxylation. To check this hypothesis, we measured the beta-decarboxylase activity in resting cells of S. carnosus grown in complex or in synthetic medium, using as substrate a beta-ketoacid, which can be an intermediate of the beta-oxidation pathway. This activity was present throughout the growth period. The enzyme appeared to be constitutive because no induction was observed. High aeration, a pH of 5 and the presence of nitrate promoted the production of methyl ketones.

Roles of superoxide dismutase and catalase of Staphylococcus xylosus in the inhibition of linoleic acid oxidation.

Staphylococcus xylosus used as starter culture in sausages decreases the level of volatile organic compounds arising from lipid oxidation and so contributes to the aroma by avoiding rancidity. The aim of this study was to characterize the roles of catalase and superoxide dismutase (SOD) in the inhibition of free fatty acid oxidation by comparing antioxidant capacity of the S. xylosus wild-type strain with those of the katA mutant and the sod mutant. Antioxidant capacity was determined by measuring the volatile organic compounds and the conjugated diene hydroperoxides arising from linoleic acid oxidation. The three strains inhibited the oxidation of linoleic acid. However, the katA mutant, and especially the sod mutant, had less antioxidant capacity than the S. xylosus wild-type strain. Thus both catalase and SOD of S. xylosus contributed to the inhibition of lipid oxidation.

A new chloramphenicol and florfenicol resistance gene flanked by two integron structures in Salmonella typhimurium DT104.

A new chloramphenicol resistance gene from Salmonella typhimurium DT104, designated floR, also conferring resistance to florfenicol, was characterized. Sequence analysis of the deduced FloR protein suggested that it belongs to the 12-TMS (transmembrane segments) multidrug efflux pumps family. The floR gene, and the downstream sequenced tetR and tetA tetracycline resistance genes, were surrounded by two class 1 integrons. The first one contained the resistance gene aadA2 and a deleted sulI resistance gene. The second one contained the beta-lactamase gene pse1 and a complete sulI gene. Thus, the floR gene is included in a multiresistance locus of at least 12.5 kb. Its particular organization and chromosomal location could be involved in the antibioresistance pattern stability of the DT104 Salmonella typhimurium strains.

Validation of random amplified polymorphic DNA assays by ribotyping as tools for epidemiological surveys of Pasteurella from animals.

Two collections of strains of Pasteurella were studied for epidemiological purposes by ribotyping and random amplified polymorphic DNA (RAPD) assays. These strains were isolated through two different structures of animal productions: cattle and rabbit. Forty strains of P. haemolytica from cattle reared in independent breeding-herds belonged to only 3 ribotypes after digestion with HindIII and PvuII. No further discrimination of these strains was obtained by RAPD assays. All these 40 strains showed more than 90% of similarity. This result was consistent with the hypothesis of a clonal dissemination of these strains in bovine herds, possible favoured by the large use of antibiotics. Forty-one strains of P. multocida were isolated in rabbits flocks belonging to 16 breeders. Six of these were linked by commercial relationships. Twenty-eight out of the 29 strains isolated through this commercial network belonged to only three ribotypes whereas the 12 strains from independant breeders belonged to 9 ribotypes. Results of RAPD assays were in accordance with those of ribotyping and validate the use of RAPD assays for epidemiological studies of Pasteurella strains.

Characterization of catalase and superoxide dismutase in Staphylococcus carnosus 833 strain.

AIMS: Staphylococcus carnosus, used as starter culture in fermented meat products, decreases the level of volatiles arising from lipid oxidation. To analyse its antioxidant capacities, catalase and superoxide dismutase (SOD) were characterized. METHODS AND RESULTS: Catalase and SOD activities were measured with spectrophotometric methods and visualized on non-denaturing polyacrylamide gels. The corresponding sod gene was identified by PCR. Southern hybridizations and enzymatic analyses showed that there was a single catalase and a single SOD in Staph. carnosus 833 strain. The gene encoding the Staph. carnosus SOD was found to encode a protein closely related to SOD requiring manganese. Catalase and SOD levels increased in mid-log phase. Only catalase was induced by oxygen, nitrate or nitrite while glucose induced neither enzyme. Metal ion limitation increased catalase and decreased SOD activities. CONCLUSION: Staph. carnosus synthesizes both enzymes in conditions encountered in sausage manufacturing. These results could explain the antioxidant properties of Staph. carnosus starter culture. SIGNIFICANCE AND IMPACT OF THE STUDY: The knowledge of the antioxidant properties of Staphylococci will allow a more rational use of these starters in meat fermented products.

Clonal diffusion of EPEC-like Escherichia coli from rabbits as detected by ribotyping and random amplified polymorphic DNA assays.

The genetic diversity and clonal relationships among 77 Escherichia coli strains isolated in France from diarrhoeic rabbits and that belonged to seven O serogroups including the predominant O103 serogroup, were estimated by ribotyping and random amplified polymorphic DNA (RAPD) assays. Fifteen ribotypes were defined. Most of the highly pathogenic O103 strains could be assigned to two major groups. Non-pathogenic strains were clearly distinguished. RAPD assays generally matched ribotyping, or gave more precision for subdividing strains from the two main O103 groups. The results on strains isolated from different areas and over a 9-year period showed the relevance of the association of these two methods for the survey of the spread of strains in breeding flocks and illustrated clonal diffusion in rabbit production structures.

Genetic diversity of Ornithobacterium rhinotracheale strains isolated from poultry in France.

Twenty-three strains of Ornithobacterium rhinotracheale from various origins, associated with respiratory pathology of birds, were compared using plasmid profiles, ribotyping and Random Amplified Polymorphic DNA (RAPD) in order to achieve a precise strain characterization as well as to highlight the relationships between these strains. No plasmid could be detected. These strains were poorly discriminated by ribotyping although different enzymes were used. The RAPD analysis has given reproducible DNA fingerprints and a good level of discrimination. This method can be used with only one or two primers to differentiate the O. rhinotracheale strains and could be used in epidemiological studies.

Tetracycline resistance determinants, Tet B and Tet M, detected in Pasteurella haemolytica and Pasteurella multocida from bovine herds.

Resistance to antibiotics has recently emerged in Pasteurella haemolytica and Pasteurella multocida isolated from bovine herds. Forty-two clinical strains resistant to antibiotics and isolated through a French national network from different origins were analysed for their resistance to tetracycline. The MICs of tetracycline ranged from 32-256 mg/L. The resistance determinants Tet B and Tet M were detected in two strains, in which they are probably chromosomal.

Characterization of high-level fluoroquinolone resistance in Escherichia coli O78:K80 isolated from turkeys.

Fluoroquinolone resistance was characterized in Escherichia coli O78:K80 isolated from diseased turkeys. The level of resistance to fluoroquinolones of the isolates appeared closely correlated with substitutions in GyrA and ParC, but not with the production of the AcrAB efflux pump. Among isolates highly resistant to ciprofloxacin (MIC 8 mg/L) and harbouring identical substitutions (two in GyrA and one in ParC), two close but distinguishable ribotypes were identified. This indicated that at least two independent selection events may have occurred.