Species identification of staphylococci and micrococci isolated from ewes' milk cheeses

Antibiotic resistance genes in coagulase-negative staphylococci isolated from food

Coagulase-negative staphylococci were isolated from different raw milk cheeses and raw meat products and screened for their antibiotic resistances. They were identified as Staphylococcus xylosus, S. lentus, S. caprae, S. epidemidis and S. haemolyticus. The most frequent resistances found were those to chloramphenicol, tetracycline, erythromycin and lincomycin. They have been characterized on the molecular level. The chloramphenicol resistance genes were localized in several S. xylosus and S. caprae on plasmids with sizes ranging from 3.8-kb to 4.3-kb and were identified as chloramphenicol acetyltransferase (cat). All the tetracycline resistant strains were identified as S. xylosus and harboured a 4.4-kb plasmid carrying the tetracycline efflux resistance gene (tetK). The two erythromycin/lincomycin resistant S. caprae and S. epidermidis strains did not hybridize with the MLSB resistance genes ermAM, ermA, ermB and ermC. Three erythromycin resistant Staphylococcus sp. strains harboured an erythromycin efflux resistance gene (msr) localized twice on a 18-kb plasmid and once on the chromosome. A S. haemolyticus strain showing resistance to both lincomycin and clindamycin harboured a linA gene-carrying 2.2-kb plasmid. Further resistances to gentamicin, penicillin and kanamycin were less frequently observed and yet not characterized on a molecular level.

Numerical taxonomy of an 'atypical' population of gram-positive cocci isolated from freshly dressed lamb carcasses

One hundred Gram-positive, catalase-positive strains were isolated from freshly dressed lamb carcasses. They were randomly selected from a non-selective medium and tested for 75 characters. Only nine cultures could be identified by conventional methods. A numerical taxonomic study was conducted on the whole population and 25 reference strains. At the 80% similarity level (Ssm), ten clusters were formed. Five of them were entirely composed of reference strains. Phena V and VIII contained seven isolates and two reference strains of Micrococcus. Phena VI (six unidentified isolates), VII (nine staphylococci) and IX (69 unidentified isolates) were more related to M. kristinae than to the remaining reference strains. Properties with possible implications in meat spoilage were: strong lipolytic activity (76%), anaerobic growth (85%), tolerance to 15% (w/v) NaCl (95%) and ability to grow at 15 degrees C (95%) and 4 degrees C (26%).