Vancomycin remains one of reserved drugs and last option for the treatment of methicillin resistant Staphylococcus aureus (S. aureus) globally. Little resistance has been reported to date, but generally it is not being actively prescribed in this environment. This study evaluated the possibility of isolating S. aureus with genes encoding resistance to vancomycin in a hospital setting. A total of 177 presumptive S. aureus were obtained from clinical specimens at the Department of Medical Microbiology Laboratory of Ahmadu Bello Teaching Hospital Shika Zaria as S. aureus isolates using nutrient agar slants. The presumed S. aureus were randomly collected from various clinical samples for a period of 8 months and further identified using standard microbiological and biochemical tests. Determinations of methicillin and vancomycin resistances were done using disc diffusion and broth dilution methods respectively. Confirmatory test for vancomycin resistance was conducted using Brain Hearth Infusion (BHI) agar plates incorporated with 4 Âµg/ml and 8 Âµg/ml Vancomycin. The minimum inhibitory concentration (MIC) of Vancomycin to the S. aureus isolated was also determined and confirmation of the presence of the vancomycin resistance genes was carried out using polymerase chain reaction (PCR). Serial culturing in an antibiotics free media was used to determine the phenotypic characteristics of the isolates. The confirmatory test carried out shows that significant percentage of the isolates [81.4% (144/177)] was S. aureus. The study showed that 25% (36/144) of the S. aureus were resistant to 30 Âµg vancomycin disc. Seventy-eight (54.1%) of the 144 isolates was discovered to be resistant to 2 or more classes of the antimicrobial agents used (multidrug resistant). Sixty-five (45.1%) VRSA were observed; and the VRSA were hetero-resistant, haven grown in BHI agar incorporated with 4 Âµg/ml and 8 Âµg/ml of vancomycin. Higher incidence of resistance was seen in wound sample (n=20) followed by urine (n=7), ear, nose and throat (n=4) and gynecological swab (n=2). But highest percentage VRSA per specimen source (50%) were observed in isolates from semen, eye swab, and wound. PCR analysis of the resistant isolates indicated that the isolates do not encode the vancomycin resistance gene. It was observed that with increasing serial dilution, greater proportion of the previously resistant isolates became susceptible and the MICs of those that were still within resistant range were discovered to be lower compared to the pre serial dilution values. This study isolated S. aureus exhibited intermediate and resistant phenotypic characteristics to vancomycin in an environment where vancomycin is not commonly prescribed.
Keywords: Antibiotic Resistance, Vancomycin, VISA, VRSA