Olatunji Kayode Aremu¹ , Josiah Ademola Onaolapo², Yakubu Kokori Ibrahim², Igwe J Chibueze³

Abstract

Purpose: To evaluate the presence of genes associated with vancomycin resistance among S. aureus isolates recovered from clinical specimens collected in a hospital setting and to assess the possibility of S. aureus harboring genes that encode resistance to vancomycin in that setting. Methods: Clinical samples of S. aureus were obtained at the Department of Medical Microbiology Laboratory of Ahmadu Bello Teaching Hospital, Shika, Zaria. Determination of vancomycin resistance and the confirmatory test were done using the broth dilution method and Brain Heart Infusion (BHI) agar plates incorporated with 4 and 8 µg/mL vancomycin, respectively. Confirmation of the presence of the vancomycin resistance genes was carried out and serial culturing in an antibiotics free media was used to determine the phenotypic characteristics of the isolates. Results: The study showed that 25 % (36/144) of the S. aureus isolates were resistant to 30 µg vancomycin disc. Sixty-five (45.1 %) vancomycin-resistant Staphylococcus aureus (VRSA) were observed and the VRSA were hetero-resistant, having grown in BHI agar incorporated with 4 µg/mL and 8 µg/mL of vancomycin. Genes that are responsible for vancomycin resistance were not found, but it was observed that with increasing serial dilution, greater proportion of the previously resistant isolates became susceptible and the minimum inhibitory concentrations (MICs) of those that were still within the resistant range were discovered to be lower compared to the pre-serial dilution values. Conclusion: This study isolated S. aureus that exhibited intermediate and resistant phenotypic characteristics to vancomycin in an environment where vancomycin is not commonly prescribed.