First report of livestock-associated MRSA ST398 in Lithuania

Abstract

Objectives: To investigate the occurrence of methicillin-resistant Staphylococcus aureus (MRSA) among food-producing animals in Lithuania and to characterize isolated strains. Methods: During 2011, 400 nasal samples were taken from livestock animals, including pigs, cattle and poultry from Lithuania. MRSA was screened on BrillianceTM MRSA 2 Agar and confirmed by PCR for the presence of the mecA gene. MRSA isolates were subjected to spa typing, SCCmec typing, ST398 PCR, and underwent PFGE analysis after Cfr9I restriction. Isolates were also tested for the presence of lukF/lukS genes, encoding the Panton–Valentine leukocidin (PVL). Antimicrobial susceptibility testing was performed using the broth microdilution method and interpreted according to CLSI guidelines. The presence of tetK, tetM, ermA, ermB, ermC, vgaA, vgaC and dfrK genes was studied by PCR. Results: Four nasal swabs out of the 400 samples were MRSA-positive (1%). The isolates were obtained from finishing pigs at slaughterhouse, all belonging to the same farm. The strains were ST398, spa type t011 and SCCmec V and none carried the PVL genes. Analysis obtained by PFGE revealed that three isolates had similar profiles, while the other clustered differently. Susceptibility testing revealed resistance to tetracycline, attributed to tet(K) and tet(M) genes, and resistance to erythromycin and clindamycin owing to the ermB gene. One MRSA strain was resistant to trimethoprim/sulfamethoxazole and carried the dfrK resistance gene. All isolates were susceptible to fluoroquinolones, mupirocin, fosfomycin, fusidic acid, rifampicin, chloramphenicol, gentamicin, netilmicin, linezolid, nitrofurantoin, teicoplanin and vancomycin. Conclusions: This study is the first report on the prevalence and characteristics of livestock-associated MRSA isolated in Lithuania. Since the MRSA strains were isolated just before slaughtering, pigs can potentially be reservoirs of bacteria... [...].