Abstract
ABSTRACT
Ten penicillin-resistant and -susceptible staphylococci, isolated from bovine mastitis milk, were studied for the presence of genes that are, or may be, involved in resistance against penicillin. The repressor (blaI), anti-repressor (blaR1), and structural (blaZ) genes of the β-lactamase-operon were found to be closely linked in all penicillin-resistant strains. The β-lactamase gene cluster was more commonly located on chromosomal rather than plasmid DNA in the strains studied. The transposase (p480) gene, which has been identified in the Staphylococcus aureus β-lactamase transposon Tn552, was found in only one single penicillin-resistant S. aureus strain. The other penicillin-resistant S. aureus isolates contained IS1181 in close location with the β-lactamase gene cluster. In only one S. haemolyticus isolate was the β-lactamase gene cluster found in close association with IS257. Penicillin-resistant S. aureus strains, which were additionally resistant to tetracycline, contained IS257 in close association with the tetracycline resistance gene (tetK). Sequence analysis of blaI, blaR1, and blaZ in two penicillin-resistant S. aureus strains revealed 94–96% sequence homology with but in staphylococci of human origin. The results indicate a predominance of class I bla transposons rather than Tn3 family class II transposons in the isolates used in this study.
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