Prevalence of the toxic shock gene (TST) in an Australian Staphylococcus aureus cohort and changes in strain prevalence and virulence genes, 1989–2003

Aim To determine the prevalence of toxic shock gene tst in an Australian Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) cohort collected over the last two decades. Method The identity of 300 S. aureus isolates was confirmed by real-time polymerase chain reaction (PCR) assays for mecA , nuc and 16S rRNA. Isolates were assayed for eight single nucleotide polymorphisms (SNPs) and for five binary genes ( pvl , cna , sdrE , pUB110, pT181). SNP profiles are concordant with multilocus sequence typing (MLST) clonal complexes (CCs) and/or sequence types (STs). Two real-time PCR assays were developed for tst , based on primer sequences previously described. Results SNP profiles correlated with 21 CCs/STs. The 90 MRSA isolates correlated with three CCs: CC239, CC1 and CC22. We found 18 tst positive isolates, 3/91 (1989), 6/104 (1996) and 9/105 (2003). Of these, CC30 was predominant. Of 210 methicillin-sensitive S. aureus isolates, 26 were CC1, 24 CC5 and 23 CC78. Conclusions The proportion of tst positive isolates and binary genes including pvl was low, and has not increased significantly. Most tst positive isolates belong to CC30 which accords with overseas publications. In 1989 and 1996 CC239 MRSA (AUS-2/3) was the sole MRSA strain. MRSA decreased significantly in 2003 in spite of the appearance of CC1 MRSA (WA-1) and CC22 MRSA (EMRSA-15).