Abstract
Staphylococcus aureus is a well-known agent of zoonotic infections. Livestock-associated methicillin-resistant S. aureus (LA-MRSA) had been receiving public health attention for over a decade. Recently, the genomes of some MRSA strains evolved further by enabling acquisition of vanA gene from enterococcus which drives the emergence of vancomycin-resistant S. aureus (VRSA), thus signaling a higher threat to antimicrobial chemotherapy and diagnostic microbiology. This study was designed to examine slaughtered chicken carcasses in Omu-Aran, North-Central Nigeria for the presence of VRSA using vancomycin agar screen (VAS) as recommended by the Clinical and Laboratories Standards Institute (CLSI). To provide independent witness to further support the evidences from VAS, a 235 bp marker for vanA gene was simultaneously detected by Original Research Article Okolie et al.; BBJ, 6(2): 87-92, 2015; Article no.BBJ.2015.030 88 PCR. From April 2013 through May 2014, chicken carcasses (n=784) were collected and studied. Among 155 (19.8%) samples which yielded S. aureus, VAS and vanA PCR methods unequivocally identified VRSA in 22 (14.2%). Compared with 46.2% VRSA report from Zaria, North-Western Nigeria, the incidence of VRSA is much less in Omu-Aran chicken carcasses than those of Zaria. Further investigation in other parts of Nigeria is recommended in order to generate nation-wide data on VRSA in this country.
Highlights
While the world battles the menace visited upon public health by horizontal gene transfer (HGT)-associated resistance to antibiotics, the recent report of methicillin resistant Staphylococcus aureus (MRSA) which transformed into vancomycin resistant S. aureus (VRSA) within the same patient [4] makes the story of VRSA more complex than MRSA
All the strains identified as VRSA by vancomycin agar screen (VAS) tested positive for vanA gene. vanA-negative strains did not grow on the vancomycin (6 mg/L) agar used for VAS
Our findings show low prevalence of VRSA compared with the Zaria study which reported 46.2% VRSA [9], it still calls for attention in the use of antibiotics in animal production
Summary
The evolution of antimicrobial resistant clones in bacteria including the staphylococci is impacting adversely on humans as well as on domesticated animals. Several reports have provided evidences for the mechainism of acquisition of mecA gene which drives MRSA as prerequisite to the acquisition via horizontal gene transfer (HGT) of vanA gene which encodes staphylococcal vancomycin resistance [1,2,3]. We isolated VRSA during routine testing of poultry and human specimens in Omu-Aran. In addition to this new finding, the possibility of emission via the airborne route [8] and there cent report of high prevalence of VRSA among poultry S. aureus in Zaria, North-Western Nigeria [9] all informed our interest in investigating chickens in Omu-Aran, North-Central Nigeria for VRSA by random sampling of retail carcasses
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