Phenotypic and Molecular Detection of Vancomycin and Methicillin Resistant Staphylococcus aureus in Clinical Isolates

Abstract

The objective of the present study was to detect methicillin and vancomycin resistance in Staphylococcus aureus (S. aureus ) isolated from clinical specimens in Khartoum State. A total of 219 of S. aureus isolates were collected from microbiology laboratory of Khartoum Teaching Hospital and microbiology laboratory of Military Hospital. The isolates were confirmed as S. aureus by phenotypic tests including Gram's stain and other biochemical tests. Modified Kirbry-Bauer disk diffusion method and brain heart vancomycin screen agar were used to detect methicillin and vancomycin resistance strains. Then E-test was applied to confirm vancomycin resistance. DNA was extracted from MRSA and VISA isolates using Muraflux kit. PCR was then performed to amplify mecA, vanA and vanB genes. Out of 219 S. aureus isolates, 155(70.7%) were found to be methicillin resistant (MRSA), sixteen were vancomycin intermediate (VISA), five strains of them with MIC 8μg/ml and nine strains with MIC 6μg/ml and two strains showed vancomycin MIC of 4μg/ml and thirteen strains of them had shown growth on Brain Heart Infusion (BHI) vancomycin screen agar (vancomycin 6 μg/ml). Molecular characterization with PCR revealed that among total (155) isolates of MRSA only 137(88.4%) possess mecA gene. However, none of VISA strains demonstrated the presence of vanA and vanB genes. In conclusion molecular characterization, confirmed the existence of methicillin resistance gene among S. aureus isolates, but this finding failed to prove the occurrence of van genes-mediated resistance among VISA isolates. Further studies are required to validate this result.