Prevalence of Staphylococcus Aureus and Qaca/b Genes Isolated From Burn Wounds at Kenyatta National Hospital and Their Association With Minimum Inhibitory Concentrations of Chlorhexidine

Abstract

Background Staphylococcus aureus (S. aureus) is one of the leading pathogens that cause severe infection of wounds of burns patients. Chlorhexidine has a broad-spectrum of activity and is therefore frequently used as a topical antiseptic agent in patients with wounds. Over the years, there have been reports of micro-organisms with lowered susceptibility to chlorhexidine. In Kenya, the prevalence of S. aureus with reduced susceptibility to chlorhexidine is unknown. In addition, the association between qacA/B genes and chlorhexidine resistance in S. aureus has not been determined in Kenyan isolates. Objective The main objective of this study was to determine the prevalence of S. aureus and chlorhexidine resistance genes qacA/B in S. aureus isolated from wounds of burns patients admitted at Kenyatta National Hospital (KNH) and their association with Minimum Inhibitory Concentrations (MICs) of chlorhexidine. Method The study design was a cross-sectional, hospital and laboratory-based study. Patients admitted at the burns ward who gave informed consent had swab specimens of their wounds cultured on Tryptic soy agar (TSA) with 5% sheep blood (KEMRI) for 24 hours at 37°C. S. aureus was identified by colony arrangement, gram stain, coagulase and catalase tests. Phenotypic resistance of S. aureus to chlorhexidine was determined by obtaining the MIC by broth dilution as described by the Clinical and Laboratory Standards Institute (CLSI 2010). DNA extraction was done by rapid lysis method using DNeasy® blood and tissue kit (Qiagen® USA). Amplification of qacA genes was performed by PCR using known primer sequences in the Applied Biosystems Veriti 96 well thermal cycler (ThermoFisher Scientific). PCR products were confirmed using 2% agarose gel electrophoresis and visualization with SYBR Green dye (ThermoFisher Scientific). xiii Results One hundred (100) swab samples were obtained from participants with burn wounds showing signs of infection. There were 34 (34%) patients with S. aureus colonization in their burn wounds. No association was found between age, gender, site of the burn wound and frequency of infection with S. aureus (p = 0.215, 0.161, 0.311 respectively). The median MIC for chlorhexidine was 128μg/ml and growth of less than half of the S. aureus isolates [41.2% (14/34)] were inhibited at this MIC. The prevalence of qacA/B was 52.9% (18/34). MIC was not significantly different between the samples with qacA/B gene and those without the gene (p = 0.878). Conclusion There is a high prevalence of S. aureus amongst admitted burns patients and emergence of chlorhexidine-resistant pathogens due to the presence of qacA/B genes in over half of the isolates. MICs were not statistically significant between isolates with qacA/B gene and those without. Reduced susceptibility to chlorhexidine indicated by MICs > 4μg/ml in the hospital environment requires further investigation to confirm the consequences of using lower chlorhexidine concentrations.