Project description:The study aims to identify genes associated with Linezolid resistance. Linezolid resistant strains were compared to a Linezolid sensitive reference strain in the presence of linezolid and absence of linezolid (mock).
Project description:In this study, we investigated the role of efflux pump genes in linezolid resistance. M. tuberculosis H37Rv cultures were exposed to sub-inhibitory concentrations of linezolid (¼ MIC) for 24 hours, and transcriptomic analysis was performed to identify upregulated genes. Of the 120 genes involved in cell wall processes, 9/120 (7.5%) were efflux pump genes, primarily belonging to the ATP-binding cassette (ABC), major facilitator superfamily (MFS), resistance nodulation division (RND), and small multidrug resistance (SMR) families. qRT-PCR, performed at 1/2, 1/4 and 1/8 MIC of linezolid, confirmed the RNA-seq results, showing that 8/9 (88.88%) of the efflux pump genes were upregulated at 1/8 MIC of linezolid, indicating that this concentration is optimal for studying efflux pump activity. These findings not only identify 1/8 MIC as optimum concentration for efflux pump studies after linezolid exposure, they also highlight the significant role of efflux pumps in linezolid resistance, providing potential targets for further research on efflux pumps in clinical isolates of M. tuberculosis.
Project description:Background: Bacterial small regulatory RNAs (sRNAs) have been implicated in important processes including antimicrobial stress response. However, the full extent of sRNA involvement in antimicrobial response in Staphylococcus aureus, an important pathogen, is incompletely understood. We investigated the transcriptional profiles of a linezolid-resistant, livestock-associated methicillin-resistant S. aureus (LA-MRSA) strain ST398 under conditions of linezolid stress. Methods: Cells in mid-exponential growth were subjected to low (8 µg/ml) and high (16 µg/ml) dose linezolid treatments followed by high throughput RNA sequencing. Read mapping and differential expression analysis were performed followed by detection and interrogation of various sRNA and mRNA transcripts. Results: Twenty-three putative regulatory RNA transcripts were expressed under low- and high-dose exposure conditions. Cis-acting regulatory elements, mainly targeting ribosomal biogenesis constituted the majority of transcriptional response with limited antisense and small RNA expression. Conclusions: This is the first study to investigate linezolid-responsive small RNA transcription in LA-MRSA strain ST398 and the first to query regulatory RNAs on a background of linezolid resistance. It provides preliminary insights and a basis for interrogating small RNAs in other strains in the quest to understand drug-responsive regulatory RNAs and identify potential anti-staphylococcal therapeutic candidates.
Project description:PoxtA and OptrA are ATP binding cassette (ABC) proteins of the F subtype (ABCF) that confer resistance to oxazolidinone, such as linezolid, and phenicol antibiotics, such as chloramphenicol. PoxtA/OptrA are often encoded on mobile genetic elements, facilitating their rapid spread amongst Gram-positive bacteria. These target protection proteins are thought to confer resistance by binding to the ribosome and dislodging the antibiotics from their binding sites. However, a structural basis for their mechanism of action has been lacking. Here by investigating 5'P mRNA decay intermediates, that provide ribosome protection data, we show that PoxtA protects against Linezolid specific stalls. Furthermore, we present cryo-electron microscopy structures of PoxtA in complex with the Enterococcus faecalis 70S ribosome at 2.9–3.1 Å, as well as the complete E. faecalis 70S ribosome at 2.2–2.5 Å. The structures reveal that PoxtA binds within the ribosomal E-site with its antibiotic resistance domain (ARD) extending towards the peptidyltransferase center (PTC) on the large ribosomal subunit. At its closest point, the ARD of PoxtA is still located >15 Å from the linezolid and chloramphenicol binding sites, suggesting that drug release is elicited indirectly. Instead, we observe that the ARD of PoxtA perturbs the CCA-end of the P-site tRNA causing it to shift by ~4 Å out of the PTC, which correlates with a register shift of one amino acid for the attached nascent polypeptide chain. Given that linezolid and chloramphenicol are context-specific translation elongation inhibitors, we postulate that PoxtA/OptrA confer resistance to oxazolidinones and phenicols indirectly by perturbing the P-site tRNA and thereby altering the conformation of the attached nascent chain to disrupt the drug binding site.