mec A Gene Profile of Methicillin-Resistant Staphylococcus aureus Isolates from Clinical Sources in Port Harcourt, Nigeria

Abstract

Staphylococcus aureus strains are responsible for a range of acute to chronic infections in humans and other animals. There is scanty information about the genetic background of S. aureus strains in Rivers State, Nigeria. The aim of this study was to determine the occurrence of MRSA among S. aureus isolates as well as detect the presence of mecA gene among methicillin-resistant Staphylococcus aureus isolates in Port Harcourt, Nigeria. Two hundred and five (205) non duplicate Staphylococcus aureus previously isolated from human sources were randomly collected from three health facilities-University of Port Harcourt Teaching Hospital, Braithwaite Memorial Specialist Hospital and De-Integrated Laboratories-all located in Port Harcourt, Nigeria, for this study from August, 2012 to July, 2013. Isolates were grouped as hospital in-patient (Hospital-acquired – Nosocomial; n = 76) and out-patient cases (community-acquired; n = 129). Isolates were reconfirmed following standard laboratory protocols and stored in duplicate -one set at +4°C (for phenotypic detection of MRSA) and another set at -70°C for molecular analysis. Using the disk diffusion method, detection of MRSA was carried out with 1µg of oxacillin (OXOID) placed on Mueller-Hinton agar with 4% NaCl supplementation). Molecular Analyses were carried out on all ORSA strains as follows-Bacterial genomic DNA extraction and PCR amplification for detection of 16S rRNA and mecA genes. Amplified products were analyzed using 2.0% agarose gel electrophoresis and subsequently visualized on a UV trans-illuminator. About twelve percent (12.2%) of the 205 Staphylococcus aureus studied were resistant to oxacillin. MRSA detection was significantly higher in in-patient isolates (23.7% of 76) than out-patient (5.4% of 129) S. aureus (p = 0.00031). Urine samples accounted for majority of the isolates (52 of 205) but MRSA detection was highest in Wound swabs (9 of 48 isolates. Of the 25 MRSA, mecA gene was detected in 17, being significantly higher in in-patient MRSA (14) than out-patient MRSA (3) (p<0-05). This study has established the presence of the methicillin resistance encoding gene-mecA, among MRSA isolates in Port Harcourt and that this gene is largely responsible for the MRSA phenotype. Study further establishes that these MRSA are more frequent in the Hospital environment. Further studies on molecular epidemiology of S. aureus are recommended in this region. Improved infection control measures in the healthcare facilities as well as sustained surveillance of methicillin-resistant S. aureus in this region are also advocated.