Effects of psm-mec on virulence gene expression. (A) Expression of selected virulence-associated genes in wild-type, psm-mec deletion and psm-mec and fudoh start codon deletion mutants in strains MSA3407 and MSA890. wt, wild-type strain; Δpsm-mec, psm-mec gene deletion strain; psm-mec*, strain harboring a psm-mec start codon mutation abolishing translation; fudoh*, fudoh (hypothetical) start codon mutation abolishing translation of hypothetical Fudoh protein. (B) Corresponding growth curves. (C) Effect of agr and agr/psm-mec deletion on spa transcription in strain MSA3407. (A, C) Gene expression was determined using qRT-PCR in late exponential phase (8-h) cultures. Values are from measurements performed at least in triplicate (three biological replicates, measured three times each) and relative to expression of the housekeeping gene gyrB. **, p<0.01; ***, p<0.001; ****, p<0.0001.