Genetic basis of rifampicin resistance in methicillin-resistant Staphylococcus aureus suggests clonal expansion in hospitals in Cape Town, South Africa

Melissa J Jansen Van Rensburg,Brenda G Elisha,Andrew C Whitelaw

doi:10.1186/1471-2180-12-46

Abstract

BackgroundSince 2001, several studies have reported high rifampicin resistance rates (45 - 100%) among methicillin-resistant Staphylococcus aureus (MRSA) isolates from South Africa. The authors previously characterised 100 MRSA isolates from hospitals in Cape Town, South Africa; forty-five percent of these isolates were rifampicin-resistant. The majority (44/45) corresponded to ST612-MRSA-IV, which is prevalent in South Africa, but has not been reported frequently elsewhere. The remaining rifampicin-resistant isolate corresponded to ST5-MRSA-I. The aim of this study was to investigate further the prevalence and genetic basis of rifampicin-resistance in MRSA isolates from hospitals in Cape Town.ResultsBetween July 2007 and June 2011, the prevalence of rifampicin-resistant MRSA in hospitals in Cape Town ranged from 39.7% to 46.4%. Based on the results of the aforementioned study, nine ST612-MRSA-IV isolates, the rifampicin-resistant ST5-MRSA-I isolate, and two rifampicin-susceptible MRSA isolates were investigated. Four previously described ST612-MRSA-IV isolates, including two each from South Africa and Australia, were also included.The ST5-MRSA-I isolate carried a single mutational change, H481Y, commonly associated with high-level rifampicin resistance. All ST612-MRSA-IV isolates carried an uncommon double amino acid substitution in RpoB, H481N, I527M, whilst one of the Australian ST612-MRSA-IV isolates carried an additional mutation within rpoB, representing a novel rpoB genotype: H481N, I527M, K579R. All ST612-MRSA-IV isolates also shared a unique silent single nucleotide polymorphism (SNP) within rpoB.ConclusionsThat local ST612-MRSA-IV isolates described here share an uncommon rpoB genotype and a unique silent SNP suggests this clone may have undergone clonal expansion in hospitals in Cape Town. Further, the data suggest that these isolates may be related to rifampicin-resistant ST612-MRSA-IV previously described in South Africa and Australia.

Highlights

Since 2001, several studies have reported high rifampicin resistance rates (45 - 100%) among methicillin-resistant Staphylococcus aureus (MRSA) isolates from South Africa
The authors recently used a combination of antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE), SCCmec typing, spa typing and multilocus sequence typing (MLST) to characterise 100 MRSA isolates obtained from hospitals in Cape Town between January 2007 and December 2008 [5]
Prevalence of rifampicin resistance among S. aureus isolates from hospitals in Cape Town The National Health Laboratory Service (NHLS) microbiology laboratory at Groote Schuur Hospital carried out antimicrobial susceptibility testing on 13 746 clinical S. aureus isolates between July 2007 and June 2011

Summary

Introduction

Since 2001, several studies have reported high rifampicin resistance rates (45 - 100%) among methicillin-resistant Staphylococcus aureus (MRSA) isolates from South Africa. The aim of this study was to investigate further the prevalence and genetic basis of rifampicin-resistance in MRSA isolates from hospitals in Cape Town. A recent national report on MRSA clones circulating in South Africa indicated that ST612-MRSA-IV was the most prevalent and widespread clone [6]. Whether these MRSA isolates were resistant to rifampicin was not reported. Prior to the Cape Town study [5] and the recently reported national investigation [6], only four clinical ST612MRSA-IV isolates had been described, including two each from South Africa and Australia, the antimicrobial susceptibility profiles of these isolates were not reported [7,8,9]

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