| Title: |
Decreased Vancomycin Susceptibility in Staphylococcus aureus Caused by IS 256 Tempering of WalKR Expression |
| Authors: |
McEvoy, Christopher R. E.; Tsuji, Brian; Gao, Wei; Seemann, Torsten; Porter, Jessica L.; Doig, Kenneth; Ngo, Dung; Howden, Benjamin P.; Stinear, Timothy P. |
| Source: |
Antimicrobial Agents and Chemotherapy ; volume 57, issue 7, page 3240-3249 ; ISSN 0066-4804 1098-6596 |
| Publisher Information: |
American Society for Microbiology |
| Publication Year: |
2013 |
| Description: |
Vancomycin-intermediate Staphylococcus aureus (VISA) strains often arise by mutations in the essential two-component regulator walKR ; however their impact on walKR function has not been definitively established. Here, we investigated 10 MRSA strains recovered serially after exposure of vancomycin-susceptible S. aureus (VSSA) JKD6009 to simulated human vancomycin dosing regimens (500 mg to 4,000 mg every 12 h) using a 10-day hollow fiber infection model. After continued exposure to the vancomycin regimens, two isolates displayed reduced susceptibility to both vancomycin and daptomycin, developing independent IS 256 insertions in the walKR 5′ untranslated region (5′ UTR). Quantitative reverse transcription-PCR (RT-PCR) revealed a 50% reduction in walKR gene expression in the IS 256 mutants compared to the VSSA parent. Green fluorescent protein (GFP) reporter analysis, promoter mapping, and site-directed mutagenesis confirmed these findings and showed that the IS 256 insertions had replaced two SigA-like walKR promoters with weaker, hybrid promoters. Removal of IS 256 reverted the phenotype to VSSA, showing that reduced expression of WalKR did induce the VISA phenotype. Analysis of selected WalKR-regulated autolysins revealed upregulation of ssaA but no change in expression of sak and sceD in both IS 256 mutants. Whole-genome sequencing of the two mutants revealed an additional IS 256 insertion within agrC for one mutant, and we confirmed that this mutation abolished agr function. These data provide the first substantial analysis of walKR promoter function and show that prolonged vancomycin exposure can result in VISA through an IS 256 -mediated reduction in walKR expression; however, the mechanisms by which this occurs remain to be determined. |
| Document Type: |
article in journal/newspaper |
| Language: |
English |
| DOI: |
10.1128/aac.00279-13 |
| DOI: |
10.1128/AAC.00279-13 |
| Availability: |
https://doi.org/10.1128/aac.00279-13; https://journals.asm.org/doi/pdf/10.1128/AAC.00279-13 |
| Rights: |
https://journals.asm.org/non-commercial-tdm-license |
| Accession Number: |
edsbas.CB4B750A |
| Database: |
BASE |