Antibiotic resistance profiles of coagulase-negative staphylococci in livestock environments.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) have globally emerged in animal husbandry. In addition to methicillin resistance, LA-MRSA may carry a variety of novel and uncommon antimicrobial resistance genes. Occurrence of the same resistance genes in coagulase-negative staphylococci (CoNS) and S. aureus suggests an ongoing genetic exchange between LA-MRSA and other staphylococci whose driving forces in the ecological niche of the farm environment are, however, still poorly understood. To assess the potential of CoNS as putative reservoirs for antibiotic resistance genes, we analysed the antimicrobial susceptibility of CoNS from dust and manure samples obtained in 41 pig farms in Germany, most of them (36 of 41) with a proven LA-MRSA/MSSA history. Among the 344 isolates analysed, 18 different CoNS species were identified and S. sciuri represented the most prevalent species (46%). High resistance rates were detected for tetracycline (71%), penicillin (65%) and oxacillin (64%) as well as fusidic acid (50%), which was mainly due to reduced susceptibility among S. sciuri isolates. S. sciuri exhibited pronounced multiresistance, and many isolates were characterised by the carriage of a number of uncommon (multi)resistance genes (e.g. cfr, apmA, fexA) and decreased susceptibility towards last resort antibiotics such as linezolid and daptomycin. The combined data suggest that S. sciuri harbours a significant resistance gene pool that requires further attention. We hypothesise that members of this species, due to their flexible lifestyle, might contribute to the spread of such genes in livestock environments.