A mutation of RNA polymerase β’ subunit (RpoC) converts heterogeneously vancomycin-intermediate S. aureus (hVISA) into ‘slow-VISA’ (sVISA)

ABSTRACT: Various mutations in the rpoB gene, which encodes the RNA polymerase beta subunit, are associated with increased vancomycin (VAN) resistance in vancomycin-intermediate S. aureus (VISA) and hetero-VISA (hVISA) strains. We reported that rpoB mutations are also linked to the expression of the recently found slow VISA (sVISA) phenotype (Saito et al 2014 AAC). Because RpoC and RpoB are components of RNA polymerase, we examined the effect of rpoC(P440L) mutation on the expression of the sVISA phenotype in the Mu3fdh2*V6-5 strain (V6-5), which was derived from a previously reported hVISA strain with the VISA phenotype. V6-5 had an extremely prolonged doubling time (72.2 min) and high vncomycin MIC (16 mg/L). However, the phenotype of V6-5 was unstable, and the strain frequently reverted to hVISA with concomitant loss of slow growth rate, cell wall thickness, and reduced autolysis. Whole genome sequencing of phenotypic revertant strain V6-5-L1 and comparison with V6-5 revealed a second mutation F562L in rpoC. Introduction of the wild-type rpoC gene using multi-copy plasmid resolved the sVISA phenotype of V6-5, indicating that rpoC(P440L) mutation expressed the sVISA phenotype in hVISA. To investigate the mechanisms of resistance in the sVISA strain, we independently isolated additional 10 revertants to hVISA and VISA. In subsequent whole genome analysis, we identified compensatory mutations in the genes of three distinct functional categories; rpoC gene itself as regulatory mutations, peptidoglycan biosynthesis genes, and relQ which is involved in stringent response. It appears that rpoC(P440L) mutation causes sVISA phenotype by augmenting cell-wall peptidoglycan synthesis, and through the control of stringent response.

ORGANISM(S): Staphylococcus aureus

PROVIDER: GSE65338 | GEO | 2015/05/08

SECONDARY ACCESSION(S): PRJNA273731

REPOSITORIES: GEO