Classification of macrolide-lincosamide-streptogramin-B-type antibiotic resistance determinants.

We have examined the relationship between the genes specifying resistance towards macrolid-lincosamide-streptogramin-B-type (MLS) antibiotics from group D and H streptococci, Staphylococcus aureus, Bacillus licheniformis, and Bacteroides fragilis by DNA annealing. We detected homology between the MLS resistance determinants from the Gram-positive cocci (streptococci and staphylococci) but not between these and the genes from B. licheniformis and B. fragilis. Based on these DNA-DNA hybridizations and on data obtained from the literature, at least four distinct classes of MLS R determinants could be defined: classes A and B for the Gram-positive cocci, class C for B. licheniformis and class D and B. fragilis. These genetic classes did not correlate with differences in phenotypic expression or in regulation (inducibility or constitutivity) of resistance towards MLS antibiotics. These findings are in favor of a recent common origin of R determinants in streptococci and staphylococci but do not suggest that gene transfer may occur between Gram-positive cocci and anaerobes (B. fragilis) despite the fact that these pathogenic bacterial genera share common human eco-systems.