Vancomycin Resistance among Methicillin Resistant Staphylococcus aureus Isolates in Uganda.

Abstract

Introduction Methicillin resistant Staphylococcus aureus is defined as Staphylococcus aureus strain resistant to almost all Beta-lactams antimicrobial agents. The increased burden of methicillin resistant Staphylococcus aureus in public health is an important concern globally. Vancomycin a glycopeptide antimicrobial agent is one of the key last resort drugs of choice for treatment of systemic infections caused by MRSA. Strains of S. aureus known as vancomycin intermediate Staphylococcus aureus (VISA) with MIC 4-8µg/Ml, show partial resistance to vancomycin whereas those with complete resistance (VRSA) have been reported elsewhere since 1990’s. However, there is insufficient data on the burden and forms of resistance to vancomycin among methicillin resistant Staphylococcus aureus isolates recovered from patients in Uganda. Aim In this study we determined the prevalence and forms of vancomycin resistance among methicillin resistant Staphylococcus aureus isolates in Uganda. We also determined the susceptibility profile of MRSA to other antimicrobial agents. Method Eighty one stored S. aureus isolates were retrieved from medical microbiology laboratory- Mulago hospital, MBN Clinical Laboratories and Central Public Health Laboratories (CPHL)-National Microbiology Referrence Laboratory. They were then screened for methicillin resistant Staphylococcus aureus, and 41 confirmed as methicillin resistant Staphylococcus aureus based on cefoxitin disc diffusion method and mecA PCR among the identified. Confirmed Methicillin resistant Staphylococcus aureus were further subjected to Minimum inhibitory concentration (MIC) using Vitek 2 Compact automated machine and vancomycin E test. S.aureus. Antimicrobial susceptibility tests (AST) and molecular assays were performed to asses phenotypic and genotypic for the presence of vanA and vanB genes in MRSA isolates respectively. Results None of the 41 methicillin resistant Staphylococcus aureus (MRSA) isolates was resistant to vancomycin. None was either VISA or VRSA. Additionally, we could not find any vanA or vanB genes. We found 100% susceptibility to linezolid and tigecycline. There was susceptibility of 80-98% to nitrofurantoin, teicoplanin, fusidic acid and rifampicin. Unfortunately, MRSA susceptibility to aminoglycosides such as tobramycin and fluoroquinolones such as levofloxacin was at less than 30%. Conclusion we therefore concluded that there is no vancomycin resistance among methicillin resistance Staphylococcus aureus isolates here in Uganda. Also other antimicrobial agents such as linezolid and tigecycline can be used as alternative way in treating infections caused by methicillin resistance Staphylococcus aureus.