Investigating the virulence and resistance genes of coagulase-negative Staphylococci

Abstract

One complication of diabetes is the development of foot ulcers which if infected, can lead to amputations. A percentage of these infections arise due to coagulase-negative staphylococci which are considered to be commensal bacteria. These organisms may harbour virulence genes such as MecA for methicillin/oxacillin resistance, VanA for vancomycin resistance, ErmA, ErmB, ErmC for erythromycin/azithromycin resistance and BlaZ for penicillin resistance as well as icaA, icaC, icaD, icaAB,, aap, atlE, embp, bhp and fbe for biofilm formation; which may enable them to become opportunistic pathogens. The hypothesis of this study is that the presence of these virulence genes increases the pathogenicity of these organisms. 108 isolates from healthy skin and tissue samples of patients suffering from diabetic foot infections were investigated for these virulence genes by various PCRs using specific primers to target these genes. Antibiotic resistance genes were more prevalent than biofilm formation genes, with the most common genes being ErmC (96.3%), BlaZ (80.6%) and MecA (69.4%). Biofilm formation genes were less prevalent, however genes such as Aap and Fbe were found in 56.5% and 48.1% respectively. Statistical analysis showed that there was no relationship between species and location sampled (p-value = 25.553) and that virulence doesn’t differ significantly between the two sampling sites (p-value = 0.665). The results indicate that coagulase-negative staphylococci isolated from healthy skin and diabetic foot ulcer tissue, possess the capacity for biofilm formation and antibiotic resistance. Therefore laboratory and clinical practices should be ideally be revised to target these potentially pathogenic organisms.