Dataset Information

Switching on antibiotic resistance in Staphylococcus aureus – Contribution of WalK and VraS histidine kinases in the development of vancomycin and daptomycin resistance

ABSTRACT: Staphylococcus aureus is a notorious bacterial pathogen that causes a broad range of human diseases, and isolates that are resistant to several antibiotic classes including last resort antibiotics like vancomycin and daptomycin complicate the situation. We characterized S. aureus VC40, a strain that shows full resistance to vancomycin (MIC of 64 µg/ml) and daptomycin (MIC of 4 µg/ml) as well as a decreased susceptibility to further cell wall active agents. Genome sequencing revealed mutations in genes encoding the histidine kinases WalK and VraS that control cell envelope related processes and gene expression profiling indicated the induction of the respective regulons in strain VC40. Reconstitution of the mutations in walK or vraS into the susceptible S. aureus NCTC 8325 background resulted in a considerably increased resistance to vancomycin and daptomycin with MICs surpassing the clinical breakpoints for these antibiotics, thereby generating vancomycin-intermediate S. aureus (VISA) strains. As observed for S. aureus VC40, the walKwalk and vraS mutations also led to an increased expression of the respective regulons in the NCTC 8325 background. Phenotypic studies showed that S. aureus VC40 as well as the walKwalk and vraS mutants of strain NCTC 8325 were characterized by a significantly thickened cell wall, a decreased growth rate, a reduced autolytic activity and an increased resistance to lysostaphin-induced lysis. These results demonstrate that the WalK and VraS histidine kinases act as major switches which allow S. aureus to rapidly develop vancomycin resistance up to the VISA level via mutation of one single gene locus and concomitantly contribute to cross-resistance to other antibiotics including the last resort antibiotic daptomycin.

ORGANISM(S): Staphylococcus aureus subsp. aureus VC40 Staphylococcus aureus

PROVIDER: GSE46887 | GEO | 2014/08/18

SECONDARY ACCESSION(S): PRJNA202922

REPOSITORIES: GEO

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Project description:The common research strain S. aureus NCTC 8325-4 was subjected to serial passage in increasing concentrations of ramoplanin. The resulting strain, RSPA16, had reduced susceptibility to not only ramoplanin but vancomycin and nisin as well. Electron microscopy revealed that the cell wall of RSPA16 was double the thickness of the susceptible progenitor strain, a phenotype commonly observed in vancomycin intermediate resistant S. aureus (VISA) strains. RSPA16 was also less susceptible to lysis induced by Triton X-100 than its progenitor strain. Transcriptional profiling experiments were performed with NCTC 8325-4 and RSPA16 without antibiotic exposure and exposed to ramoplanin. Increased expression of genes associated with cell wall stress was observed when either strain was treated with ramoplanin. We also observed that treatment with ramoplanin altered of the expression levels of numerous genes encoding proteins involved with amino acid biosynthesis, central metabolic pathways, nucleotide biosynthesis, iron acquisition, ABC transporters and regulation of transcription. Comparison of the transcriptional profiles of RSPA16 and NCTC 8325-4 not exposed to ramoplanin revealed alterations in the expression of levels of several genes involved with biosynthesis of teichoic acids, biosynthesis of peptidoglycan, central metabolism, DNA replication, nucleotide biosynthesis, iron acquisition, ABC transporters, and regulation of transcription. These transcriptional profiles provide insights into the possible sources of the reduced susceptibility of RSPA16 to peptide antibiotics. Mid log phase (OD620 = 0.4) batch TSB cultures of ramoplanin susceptible (NCTC 8325-4) and resistant (RSPA16) strains of S. aureus were exposed to ramoplanin for 30 minutes at 37 C. Untreated controls were performed for each strain as well. The transcriptional response was determined using Affymetrix Gene Chip Arrays. This study also examines the transcriptional alterations which confer reduced susceptibility to ramoplanin as the transcriptional profiles of NCTC 8325-4 and RSPA16 each untreated were compared.

Dataset Information

Switching on antibiotic resistance in Staphylococcus aureus – Contribution of WalK and VraS histidine kinases in the development of vancomycin and daptomycin resistance

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