Figure 4. TSST-1 and total mitogen production in vitro by tst-positive clonal complex (CC) 30 MSSA and CC30 MRSA strains. A) Mean TSST-1 present in the culture supernatants of tst-positive CC30 MSSA (n = 81) and CC30 MRSA (n = 39) isolates measured by immunoblot after overnight culture in brain–heart infusion broth. B) Mean human PBMC proliferative response to culture supernatants of tst-positive CC30 MSSA (n = 77) and CC30 MRSA (n = 39) isolates. Negative indicates RPMI tissue culture medium (Invitrogen, Hemel Hempstead, UK) alone. Error bars indicate SDs. *p<0.05; ***p<0.0001 (both by 2-tailed t-test). cpm, counts per minute; MSSA, methicillin-sensitive S. aureus; MRSA, methicillin-resistant S. aureus; PBMC, peripheral blood mononuclear cells; TSS, toxic shock syndrome; TSST-1, TSS toxin 1.