Vancomycin-Resistant <i>Staphylococcus</i> aureus Isolates from HIV Positive Patients in Imo State, Nigeria

Abstract

Vancomycin continues to be an important antimicrobial agent for treating infections caused by <i>Staphylococcus</i> aureus strains that are resistant to oxacillin (MRSA) and other antimicrobial agents. Vancomycin-resistant <i>Staphylococcus aureus</i> (VRSA) isolates were obtained from HIV-positive patients already on HAART treatment but were not admitted in the hospital. Species identification was confirmed by standard biochemical tests and PCR amplification of the 16S rRNA gene. Vancomycin resistance was determined using the Kirby-Bauer diffusion method and confirmed by Brain Heart Infusion (BHI) vancomycin screen agar plate containing 6µg/ml vancomycin. A total of 8 VRSA were identified from the 59 isolates obtained from the patients. Five out of the eight VRSA isolates were resistant to all the antibiotics tested. However, one unusual strain which was resistant to all the antimicrobial agents tested contained no plasmid, <i>Mec</i> A gene and PVL toxin gene. One VRSA isolate contained a large plasmid (~21.2 kb) and four small plasmids of ~5, 2.5, 1.2 and 0.8 kb respectively. The minimum inhibitory concentration (MIC) for vancomycin susceptibility was >15 µg/ml at disk potency of 30µg. The reduced susceptibility of S. <i>aureus</i> strains to vancomycin leaves clinicians with relatively few therapeutic options for treating these infections and therefore emphasizes the importance of prudent use of antibiotics and the use of infection-control precautions to prevent their transmissions.