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Transcriptional Analysis of S. aureus Response to Ramoplanin

ABSTRACT: 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.

ORGANISM(S): Staphylococcus aureus

PROVIDER: GSE14669 | GEO | 2009/02/04

SECONDARY ACCESSION(S): PRJNA112363

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.

Project description:The phenotype “intermediate vancomycin resistance” in Staphylococcus aureus (CLSI: MIC = 4-8 mg/L) has been assigned to changes that lead to alterations in cell wall synthesis and morphology. Most vancomycin intermediately resistant S. aureus (VISA) strains are characterised by an increased cell wall thickness as a consequence of an activated cell wall biosynthesis and decreased autolysis. The purpose of this study was to analyse the genetic basis of the vancomycin resistance mechanism of the clinical VISA isolate SA137/93A and its spontaneous mutant strain SA137/93G. The methicillin-resistant S. aureus (MRSA) SA137/93A was isolated from a tracheal secretion and displays heterogeneous intermediate vancomycin resistance (hVISA strain, MIC: 8 mg/L in BHI). Subculturing in presence of 6 mg/L vancomycin generated a mutant with homogeneous intermediate vancomycin resistance, that showed an MIC value of 16 mg/L in BHI and was designated SA137/93G. PFGE profiles and phage typing of the strains showed that they were members of the Iberian clone (ST247), which was prevalent in Germany in the early nineties under the designation “Northern German epidemic strain”. Both strains possess a thickened cell wall. However, the vancomycin resistance of strain SA137/93A is most probably enhanced by an increased amount of free D-Ala-D-Ala termini in the cell wall, which is due to decreased crosslinking, whereas the mutant strain SA137/93G shows normal crosslinking. Moreover, strain SA137/93A displays an increased expression of the essential two-component system yycFGHI as a consequence of an IS256 insertion in the promoter region, while strain SA137/93G is characterised by an insertion of IS256 into the gene tcaA. Although both insertions were shown to correlate with a decrease in susceptibility to vancomycin, the difference in the vancomycin resistance level of the strain pair could be mainly attributed to the disruption of tcaA in the mutant.This study was conducted to identify resistance mechanisms that both strains might have in common. To this end we compared the transcriptomes of both strains with that of the closely related vancomycin susceptible MRSA/VSSA strain SA1450/94 (MIC: 2 mg/L). We found that the genes of the capsule biosynthesis were the only genes with higher expression in both VISA strains. Keywords: strain comparison

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Transcriptional Analysis of S. aureus Response to Ramoplanin

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