Distribution of mecA gene amongst Staphylococcus aureus isolates from Southwestern Nigeria

Abstract

Staphylococcus aureus (S. aureus) is an important pathogen in human infections and is implicated in a wide variety of infections, from mild skin infections to more serious and invasive infections. Methicillin resistant S. aureus (MRSA) is one of the major causes of nosocomial infection in hospital setting. The study was aimed at determining the distribution of mecA gene among the S. aureus isolates from south western tertiary hospitals, Nigeria. In this study, a total of 194 isolates of S. aureus were collected from the specimen submitted to diagnostic section of Medical Microbiology Department, University College Hospital (UCH) Ibadan, Obafemi Awolowo University Teaching Hospital, Ile-Ife, and LAUTECH Teaching Hospital (LTH) Osogbo, in the South Western Nigeria. Antibiotics susceptibility testing including methicillin sensitivity testing, beta lactamase testing, PCR for detection of mecA gene, and minimum inhibitory concentrations to methicillin were carried out on all the 194 isolates of S. aureus. Among the 194 strains, 40 (20.6%) were MRSA using 10 μg methicillin disc. PCR analysis showed that mecA gene was present only in 43 (22.2%) of 194 S. aureus isolates. Minimum inhibitory concentration (MIC) was also carried out to determine the degree of resistant of the isolates showed that the MIC₅₀ and MIC₉₀ for MRSA or mecA⁺ were > 128 μg/ml while the MIC₅₀ and MIC₉₀ for mecA^- were 0.5 and 2 μg/ml, respectively. Furthermore, 124 (64 %) of the 194 S. aureus isolates were β-lactamase producers. The study found that there were strong associations between isolation site of specimens / nature of specimens (Χ²= 16.74; p < 0.05), beta lactamase producing S. aureus strains (Χ²= 29.21; p < 0.05) and no association was found between the hospitals, gender, age and the prevalence of MRSA in this study (p > 0.05). The study concludes that the prevalence of mecA gene in S. aureus in South Western, Nigeria is 22% and mecA gene detection is a good predictor of methicillin resistance in S. aureus in Nigeria, hence use as a method of detection of MRSA

Keywords: Staphylococcus aureus, mecA gene, MRSA, antibiotic resistance, Nigeria.