Background: Staphylococci are some of the most common causes of infections in birds. Worldwide, the dramatic increase in the prevalence of antimicrobial-resistant Staphylococcus aureus (S. aureus) is receiving widespread attention, due to multi-resistant strains, diminishing the usefulness of antibiotics in human medicine and, thereby limiting therapeutic options. Objectives: In this study, we characterized the distribution and antibiotic resistance patterns of methicillin resistant S. aureus (MRSA) strains, isolated from lying hen farms in Karaj, Iran. The pulsed field gel electrophoresis patterns and the staphylococcus cassette chromosome mec (SCCmec) types were also determined. Materials and Methods: Over a period of 90 days (collected at days: 0, 45, 90) during 2013, nine samplings, consisting of swab samples and litter collection, were done from three poultry farms (three each) and a total of 55 MRSA isolates were isolated from chromogenic MRSA selective agar. The clonality of MRSA strains was determined using pulsed field gel electrophoresis (PFGE) and the diversity in the structure of SCCmec elements and also different ccr types was studied. Susceptibility to seventeen antibiotics was determined, using disc diffusion method, according to Clinical and Laboratory Standards Institute recommendation. Results: Out of the 55 MRSA strains, all isolates were at least resistant to penicillin, 58% showed resistance to erythromycin and 55% were resistant to ciprofloxacin. On the other hand, all isolates showed susceptibility to vancomycin, quinuprostin-dalfopristin, linezolid, fusidic acid, nitrofurantoin and minocycline. The results of PFGE showed diverse pulsotypes, consisting of 13 common types and 18 single types, with seven common PFGE types, which were found among the MRSA strains, isolated from different farms, suggestive of an epidemiological link. Moreover, 67% of MRSA isolates shared SCCmec type III and showed type 3 ccr, indicating the hospital origin of the strains.
Conclusions:The results of this study illustrated the persistence of resistant bacteria in the environment, and highlight the reservoir of resistance, associated with use of antibiotics, as feed additive in poultry production.
