Emergence of clinical vanA-type vancomycin-resistant Staphylococcus aureus isolates in National Orthopaedic Hospital Dala, Kano, Nigeria

Abstract

Background: The increasing prevalence of multi drug resistance (MDR) in strains of Staphylococcus aureus is a major challenge in the selection of an appropriate therapeutic agents, especially in persistent orthopaedic infections. This study investigated the patterns of antimicrobial resistance and identified the genetic determinants of resistance in S. aureus isolates from orthopaedic patients.

Methodology: This was a descriptive cross-sectional study of hospitalized patients at National Orthopaedic Hospital Dala (NOHD), Kano, Nigeria from whom urine samples, and nasal and wound swabs were collected for isolation of S. aureus. Samples were cultured on standard media and S. aureus isolated and identified using both conventional biochemical tests and a standard rapid diagnostic kit. The antibiotic susceptibility was determined to a panel of 15 antibiotics using the modified Kirby-Bauer disc diffusion method. Vancomycin minimum inhibitory concentration (MIC) of each isolate was determined using vancomycin Epsilon-test strip. mecA and vanA were detected by multiplex polymerase chain reaction (PCR) assay.

Results: From the total of 134 samples, S. aureus was isolated from 36 (26.8%); 10 (7.4%) from urine, 13 (9.7%) from nasal swab, and 13 (9.7%) from wound swab. Thirty-four (94.4%) isolates were phenotypically methicillin (cefoxitin) resistant (MRSA), while 2 (5.6%) isolates were methicillin sensitive (MSSA). Phenotypic resistance rate of the S. aureus isolates was highest to gentamicin (94.4%), followed by penicillin (88.8%), cephalosporins and fluoroquinolones (87.4%), while rate was lowest to vancomycin (11.1%, 4/36). Seventeen (47.2%) were MDR, 16 (44.4%) were extensively drug resistant (XDR), and 2 (5.6%) were pan-drug resistant (PDR) S. aureus isolates. The mecA gene was detected in 4 (11.8%) of the 34 phenotypic MRSA isolates and vanA genes in 2 (50.0%) of the 4 phenotypic VRSA isolates.

Conclusion: The detection of vanA and mecA in clinical S. aureus isolates in this study is an indication that clinical VRSA has emerged in MRSA population in Nigeria. This emergence can pose a major threat to primary care-givers and a public health challenge among the daily inhabitants of National Orthopaedic Hospital Dala (NOHD), Kano and the community at large.