Treatment of Staphylococcus aureus infections is often reliant on last line antibiotics, such as linezolid. Reduced susceptibility to last line agents is increasing but the molecular basis for this phenomenon is not well understood. Here, we investigated the transcriptional changes in clinical methicillin-resistant S. aureus following linezolid exposure.
The OD6000.5 bacteria culture was treated with 0.5x MIC linezolid for 30 minutes. The RNA was extracted immediately and underwent the cDNA synthesis and Illumina sequencing. The experiment was conducted with four biological repeats and resulting reads were mapped onto a reference genome. The read counts were normalized and analysed to compare the expression of protein-coding and non-protein-coding genes.
Linezolid exposure has a global impact on gene expression. Overall, we found 1007 genes were upregulated and 1143 genes were downregulated. As expected, all ribosomal proteins RNA were upregulated except rpsA, which encodes small subunit ribosomal protein S1. Furthermore, many two component regulators were also dramatically altered with the upregulated of saeS/R, vraS/R, arlS/R and vraS/R, and downregulated transcription of lytS/R and nreB/C. Interestingly, most genes related to staphylococcal infection were upregulated. The upregulation of genes clfB, isdA, sdrC and sdrD may indicate increasing colonisation potential; upregulation of the genes sbi, efb, ecb and SCIN may contribute to bypass of the complement complex attack; and the genes associated with antimicrobial peptides resistance, such as vraF, vraG, dlt, mprF, and aur were all upregulated. These data predict that S. aureus may present a more persistent phenotype under treatment with linezolid. We also discovered the expression of small regulatory RNAs were also significantly changed. Among 409 annotated sRNA genes, 330 showed significant changes in expression following linezolid treatment.
This study highlights the S. aureus transcriptional response under linezolid exposure, and is leading to a deeper understanding of the full impact of antibiotic treatments.