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Transcriptional profiles of Staphylococcus aureus strains in the presence of the lantibiotic mersacidin.

ABSTRACT: The lantibiotic mersacidin is an antimicrobial peptide of 20 amino acids that is ribosomally produced by Bacillus sp. strain HIL Y-85,54728. Mersacidin acts by complexing the sugar phosphate head group of the peptidoglycan precursor lipid II, thereby inhibiting the transglycosylation reaction of peptidoglycan biosynthesis. Here, we studied the transcriptomic response of S. aureus to subinhibitory concentrations of mersacidin using microarray and qRT-PCR techniques. The transcriptomics revealed an extensive induction of the cell wall stress response of S. aureus, which is partly controlled by the two-component regulatory system VraSR. In contrast to other cell wall-active antibiotics such as vancomycin, 0.2 x MIC of mersacidin was sufficient for induction. Interestingly, the cell wall stress response was equally induced in vancomycin intermediate resistant S. aureus (VISA) as well as in a highly susceptible strain. Furthermore, the efficiency of mersacidin was not affected by an increased cell wall thickness, which is part of the VISA-type resistance mechanism. Since the transcription of the VraDE ABC transporter genes was induced up to 1700-fold in our experiments, we analyzed the role of VraDE in the response of S. aureus to mersacidin. Unexpectedly, the deletion of the vraE gene did not result in an increased susceptibility to mersacidin compared to the wild type strain. In conclusion, mersacidin appears to be a strong inducer of the cell wall stress response of S. aureus at very low concentrations, which reflects its general mode of action as a cell wall-active peptide as well as its use of a unique target site on lipid II. Keywords: antibiotic induced response

ORGANISM(S): Staphylococcus aureus subsp. aureus N315 Staphylococcus aureus

PROVIDER: GSE9261 | GEO | 2008/10/23

SECONDARY ACCESSION(S): PRJNA102887

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.

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Transcriptional profiles of Staphylococcus aureus strains in the presence of the lantibiotic mersacidin.

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