Resistance behaviour of inducible clindamycin-resistant staphylococci from clinical samples and aquatic environments

In this study, the species diversity of staphylococci with inducible resistance to macrolides, lincosamides and streptogramin B (MLSB) isolated from clinical samples, sewage and river water was investigated. Inducible clindamycin resistance was tested using a D-test and macrodilution assays. Inducible cross-resistance (iMLSB phenotype) was examined by PCR of erm gene classes A, B, C, F, G, Q, T and 43. Although ermC was the most frequently detected resistance gene in iMLSB phenotypes of environmental staphylococci (61.2%), resistance genes encoding iMLSB were more diverse than in staphylococci from hospital samples. In 22.4% of iMLSB staphylococci from aquatic environments, none of the eight tested erm genes was found. Those isolates and erm43-expressing Staphylococcus lentus displayed low erythromycin MICs (3-16 µg ml(-1)) compared with ermC-positive environmental staphylococci (≥256 µg ml(-1)). In contrast to clinical isolates with clearly defined resistance behaviour, resistance patterns against MLSB and MICs for clindamycin of environmental isolates were more diverse. Although the abundance of iMLSB staphylococci in the aquatic environment was lower than in staphylococci from hospital samples, the diversity of resistance genes encoding this phenotype seemed to be higher. Oleandomycin is the best marker to correlate iMLSB phenotype and the respective erm gene. The phenotypical behaviour of environmental isolates may differ from the resistance pattern of clinical iMLSB staphylococci expressing ermA or ermC, and this should be considered for successful treatment of infections.