ABSTRACT
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.
Subject(s)
Anti-Bacterial Agents/pharmacology , Coagulase/metabolism , Drug Resistance, Microbial/genetics , Food Microbiology , Staphylococcus/drug effects , Staphylococcus/isolation & purification , Animals , Cheese/microbiology , Chloramphenicol Resistance/genetics , Meat Products/microbiology , Microbial Sensitivity Tests , Nucleic Acid Hybridization , Staphylococcus/classification , Staphylococcus/genetics , Tetracycline Resistance/geneticsABSTRACT
For 77 strains of Staphylococcus aureus freshly isolated from different foods, growth, enterotoxin and TNase production were determined in intervals of 1.5 degrees C +/- 0.5 degrees C by cultivating them in a temperature-gradient incubator between 5 and 50 degrees C for up to 7 days. All the strains were coagulase, DNase and lysostaphin positive but only 58% formed one or two enterotoxins type SEA, SEB or SEE. All strains grew within 7 days in brain heart infusion and had lower and upper temperature limits for growth and TNase production of between 6.5 and 12.5 degrees C, and 39.5 and 48.5 degrees C respectively. The lower and upper temperature limits for production of enterotoxins were between 14 and 38 degrees C, and between 35 and 44 degrees C respectively. Enterotoxin forming isolates either showed narrow (3 to 4 degrees C) or wide (10 to 20 degrees C) ranges of enterotoxin production, irrespective of their temperature range of growth and TNase production. None of the 12 specific physiological attributes used for differentiation could be correlated to toxin type or the temperature requirement of the toxin production. No correlation between the origin and the physiological characters could be detected.
