title: Genetic basis of rifampicin resistance in methicillin-resistant Staphylococcus aureus suggests clonal expansion in hospitals in Cape Town, South Africa.
abstract: BACKGROUND
  Since 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.
  
  
  RESULTS
  Between 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.
  
  
  CONCLUSIONS
  That 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.
authors.affiliation: Division of Medical Microbiology, Faculty of Health Sciences, University of Cape Town, Observatory, Cape Town 7925, South Africa.
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Jansen van Rensburg
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Whitelaw
authors.forename: Brenda G
authors.initials: BG
authors.lastname: Elisha
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D005838:Genotype; D006761:Hospitals; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D020641:Polymorphism, Single Nucleotide; D012293:Rifampin / Q000494:pharmacology*; D013019:South Africa / Q000453:epidemiology; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D012293:Rifampin