Molecular basis of resistance to macrolides; lincosamides and streptogramins in clinical isolates

International audience; The aim of this study was to evaluate the prevalence of resistance to macrolide-lincosamide-streptogramin (MLS) antibiotics as well as to assess the molecular basis of this resistance among 72 urinary isolates collected from 2005 to 2009 in University Hospital of Caen (France). Of the 72 strains studied, 33 (45.8%) were resistant to at least one MLS antibiotic, including 24 (72.7%) with an M phenotype, 5 (15.2%) with an inducible MLS phenotype, 3 (9.1%) with a combined M+L phenotype and 1 (3.0%) with an L phenotype. All isolates were susceptible to the combination of streptogramins A and B. The resistance genes (A), (B), (C), (A) and (A) were detected alone in 0, 0, 5 (15.2%), 24 (72.7%) and 1 (3.0%) of the 33 MLS-resistant isolates, respectively, whereas 2 strains (6.1%) were positive for both (A) and (A). All (A)-positive isolates exhibited an M phenotype, whereas all five (C)-positive and all three (A)-positive strains displayed, respectively, an inducible MLS phenotype and an L phenotype with a positive Hodge test. Plasmid analysis indicated that (C) and (A) genes were borne by small-size plasmids (ca. 2.5kb), whereas larger plasmids (30-90kb) harboured (A). In conclusion, these findings show a high prevalence of MLS resistance in , which was mainly associated with the presence of the (A) gene. Since colonises the gastrointestinal tract, it may constitute an unexpected reservoir for MLS resistance genes, in particular (A), among coagulase-negative staphylococci.