ABSENCE OF mecA GENE IN METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS ISOLATES

Abstract

Methicillin-resistant Staphylococcus aureus has emerged as a serious threat to public health, causing both hospital and community-associated infections. The gold standard for MRSA detection is the amplification of the mecA gene that codes for the production of the altered penicillin-binding protein (PBP2a) responsible for classical methicillin resistance. This work determined the nature of methicillin-resistance observed in staphylococcal isolates. Staphylococcus aureus isolates with phenotypic resistance to methicillin (oxacillin) were tested for the carriage of the mecA gene by multiplex PCR to detect and type the SCCmec. The isolates were tested for the production of the altered PBP2a by latex agglutination test and β-lactamase production/hyper production by microplate Nitrocefin assay. None of the isolates hybridized with any of the 16 sets of primers representing the five major SCCmec types, nor contained the mecA gene; and none was positive for the gene product PBP2a determined by the MRSA screen latex agglutination test. Majority of the isolates 72.2 % (26/36) tested positive for β-lactamase production while 11/26 (42.3%) were β-lactamase hyper producers. The MRSA phenotype observed in the isolates was not the classical mecA-mediated resistance, but most probably due to hyper-production of β-lactamase. Reports of loss of the mecA gene (believed to be stable) during storage and the fact that all PCR detection of mecA gene reported in Nigeria were done outside the country calls for attention on building local capacity for prospective molecular screening for MRSA in clinical and environmental isolates to adequately document their prevalence and monitor the increase. Appropriate guidelines should also be drawn up for the proper screening and reporting of MRSA isolates with the establishment of regional Reference Laboratories.