The Distribution of Acme Gene and MRSA Related Virulence Genes in Staphylococcus Aureus Strains from Nigeria

Background: Arginine Catabolic Mobile Element (acme) is a Staphylococcal genomic island that enhances fitness and ability of bacteria cells to colonize on mucous membrane and skin. It is stongly associated with the epidemic and virulent S. aureus USA 300. This study determined the distribution of acme and Methicillin Resistant Staphyllococus Aureus (MRSA)-related genes in S. aureus isolated from patients in five tertiary hospitals in Nigeria. Methods: A total of 51 S. aureus isolates from the clinical specimens submitted to laboratories in five tertiary hospitals in Nigeria were used in this study. Phenotypic and genotypic identifications of the S. aureus were performed. Antibiotic Susceptibility Test (AST) was carried out to determine the susceptibility pattern of the isolates using various antibiotics discs. Minimum Inhibitory Concentration (MIC) was used to determine the degree of resistance of the isolates to methicillin and vancomycin. Polymerase Chain Reaction (PCR) was used to screen for the presence of mecA, acme sae, sarA, PVL, α-psm and norB genes using specific primers. The SCCmec type was determined for all the MRSA isolates using polymerase chain reaction. Results: The MIC for mecA negative strains was ≤4 µg/ml, while the MIC for mecA positive was 8 µg/ml. mecA gene was detected in 35 (68.6%) of 51 strains of S. aureus. The prevalence of sae, sarA, mecA, acme, PVL, α-psm and norB gene were estimated to be 70.6%, 68.6%, 68.6%, 29.4%, 5.1%, 39.2% and 33.3% respectively. There was an association between the distribution of mecA+ and norB+ strains (P = 0.034) and the hospitals (P =0.008) where the isolates were obtained from, whereas there was no association between acme positive strains and the hospitals (P = 0.669) from which the isolates were obtained from. Also, there was no association between mecA, norB, acme with the sex, age and hospital admission status (P>0.05). Furthermore, there was an association between PVL gene and the two geographical regions (South-Western and North-Western, Nigeria) (χ2 = 7.77; p < 0.05). The SCCmec typing showed that 21 (60.0%) out of the 35 MRSA used in this study carried the SCCmec type elements such as type I, II, III and VIII which were all the characteristic of HA-MRSA while the remaining 14 (40%) carried the SCCmec type elements such as type IV, V, VI and VII which were all characteristic of CA-MRSA. Thus the overall prevalence of HA-MRSA and CA-MRSA in this study was 60.0% and 40.0%, respectively. Conclusion: The prevalence of acme and α-psm genes in S. aureus are high and this is a novel discovery in Nigeria which has opened a new era in the transmission and fitness of circulating MRSA in causing infection in the community at large. The study concluded that there is high prevalence of HA-MRSA in South-Western, Nigeria and high prevalence of CA-MRSA in the North-Western, Nigeria.