Activities of vancomycin, teicoplanin and linezolid against bacteraemic methicillin-resistant Staphylococcus aureus strains in Gauteng, South Africa

Introduction

This study aims to describe the vancomycin, teicoplanin and linezolid susceptibility patterns of methicillin-resistant Staphylococcus aureus (MRSA) blood culture isolates from patients in the private sector in Gauteng, South Africa. Screening tests for heterogeneous glycopeptide intermediate S. aureus (hGISA) strains were also performed. MRSA isolates with vancomycin minimum inhibitory concentrations (MICs) of 1 to 2 mg/l are associated with worse clinical outcomes [1]. Furthermore, hGISA infections are associated with clinical failure of glycopeptide therapy [2].

Methods

MICs for vancomycin, teicoplanin and linezolid were performed on 50 randomly collected MRSA strains from blood cultures according to Clinical Laboratory Standards Institute guidelines. Screening for hGISA was performed using the Etest (AB BIODISK) Macromethod as well as the new Etest Glycopeptide Resistance Detection.

Results

The results of susceptibility patterns are depicted in Table 1. Fifty percent (25/50) and 20% (10/50) of the strains screened positive for hGISA using the Etest Macromethod and Etest Glycopeptide Resistance Detection, respectively.

Table 1 Susceptibility patterns of MRSA isolates (n = 50)

Conclusion

We recommend that clinically relevant MRSA isolates be reported with MICs for vancomycin, teicoplanin and linezolid, and that glycopeptide treatment failure warrants further testing of the MRSA isolate to detect possible hGISA. Ideally hGISA should be confirmed by population analysis profile testing, which was not available to us for this study.