Comparison of genes involved in penicillin resistance in staphylococci of bovine origin

Ten penicillin-resistant and -susceptible staphylococci, isolated from bovi ne mastitis milk, were studied for the presence of genes that are, or may b e, involved in resistance against penicillin. The repressor (blaI), antirep ressor (blaR1), and structural (blaZ) genes of the beta-lactamase-operon we re found to be closely linked in all penicillin-resistant strains. The beta -lactamase gene cluster was more commonly located:on chromosomal rather tha n plasmid DNA in the strains studied. The transposase (p480) gene, which ha s been identified in the Staphylococcus aureus beta-lactamase transposon Tn 552, was found in only one single penicillin-resistant S, aureus strain. Th e other penicillin-resistant S, aureus isolates contained IS1181 in close l ocation with the beta-lactamase gene cluster, In only one S, haemolyticus i solate was the beta-lactamase gene cluster found in close association with IS257, Penicillin-resistant S, aureus strains, which were additionally resi stant to tetracycline, contained IS257 in close association with the tetrac ycline resistance gene (tetK), Sequence analysis of blaI blaR1, and blaZ in two penicillin-resistant S, aureus strains revealed 94-96% sequence homolo gy with bla in staphylococci of human origin, The results indicate a predom inance of class I bla transposons rather than Tn3 family class II transposo ns in the isolates used in this study.