Project description:Daptomycin (DAP) is the last-resort treatment for heterogeneous Vancomycin-Intermediate-Staphylococcus aureus (hVISA) and Vancomycin-Intermediate-S.aureus (VISA), and DAP-resistance onset which is also linked to reduced vancomycin susceptibility, is an increasing public health problem. To have more insight into the mechanisms of daptomycin resistance, the comparative transcriptomes of two DAP-R (1C-3B) clinical isogenic isolates vs their DAP-S (1A-3A) counterparts were investigated by Illumina RNA-seq, the Rockhopper tool, computational filtering analyses and bioinformatic tools.
Project description:Transcriptional response of Bacillus subtilis to daptomycin in wild-type and in a daptomycin resistant mutant. Bacillus subtilis 168, WT (-DAP) vs. DapR1 (-DAP), WT (+DAP) vs. DapR1 (+DAP), DapR1 (+DAP) vs. DapR1 (-DAP). Each experiment was conducted at least twice using two independent total RNA preparations. For daptomycin untreated comparison between 168 WT and DapR1 mutant, DapR1 was labeled with Alexa Fluor 647 and WT was labeled with Alexa Fluor 555. For daptomycin treated experiments between WT and DapR1, DapR1 was labeled with Alexa Fluor 647 and WT with Alexa Fluor 555. For treated vs. untreated DapR1, the DAP treated samples were labeled with Alexa Fluor 647 and the untreated with Alexa Fluor 555. For dye swap, untreated DapR1 was labeled with Alexa Fluor 647 and DAP treated with Alexa Fluor 555.
Project description:Several groups have shown that through evolution experiments, tolerance and resistance evolved rapidly under cyclic antibiotic treatment. In other words, intermittent antibiotic exposure performed in a typical adaptive laboratory evolution (ALE) experiments will “train” the bacteria to become tolerant/resistant to the drug. Using this experimental strategy, we performed in vitro laboratory evolution in MRSA using daptomycin, and mine novel daptomycin tolerance and resistance mutants, which were isolated at specific time points during the evolution experiments. Three daptomycin-tolerant isolates with different tolerance level were generated from our laboratory evolution (TOL2 and TOL5 with a mild-tolerance phenotype, and TOL6 with a high-tolerance phenotype). They all bear mutations at different genes, and have no increase in MIC towards daptomycin. Besides, we also isolated three daptomycin-resistant isolates (RES1, RES2, RES3) that have a single point mutation in the same gene, mprF, but at different locations, leading to an increased MIC towards daptomycin. Through proteomics, we uncovered the differential adaptation strategies of these daptomycin tolerant and resistant MRSA strains, and how they respond differently to antibiotics compared to the ancestral wild-type.
Project description:Mutants from SG511 and NCTC8325 (wild type isolates) resistant to daptomycin were obtained following serial passage experiments in vitro. Transcriptomic experiments showed alteration in the expression of genes involved in various pathways including general metabolism, cell wall regulon and lipid metabolism. Microarray was used to evaluate alteration in the transcriptome between wild type strains SG511 and NCTC8325 and their daptomycin resistant isolates, in antibiotic-free medium.
Project description:Abstract of associated manuscript: Daptomycin is the first of a new class of cyclic lipopeptide antibiotics used against multidrug-resistant Gram-positive pathogens. The proposed mechanism of action involves disruption of the functional integrity of the bacterial membrane in a Ca2+-dependent manner. We have used transcriptional profiling to demonstrate that treatment of Bacillus subtilis with daptomycin strongly induces the lia operon including the autoregulatory LiaRS two-component system (homologous to Staphylococcus aureus VraSR). The lia operon protects against daptomycin and deletion of liaH, encoding a phage shock protein A (PspA)-like protein, leads to 3-fold increased susceptibility. Since daptomycin interacts with the membrane, we tested mutants with altered membrane composition for effects on susceptibility. Deletion mutations of mprF (lacking lysyl-phosphatidylglycerol) or des (lipid desaturase) increased daptomycin susceptibility, whereas overexpression of MprF decreased susceptibility. Conversely, depletion of the cell for the anionic lipid phosphatidylglycerol led to increased resistance. Fluorescently-labeled daptomycin localized to the septa and in a helical pattern around the cell envelope and was delocalized upon depletion of phosphatidylglycerol. Together, these results indicate that the daptomycin-Ca2+ complex interacts preferentially with regions enriched in anionic phospholipids and leads to membrane stresses that can be ameliorated by PspA family proteins. Bacillus subtilis W168, WT (+DAP) vs. WT (-DAP). The experiment was conducted in triplicate using three independent total RNA preparations. For WT-rep1 and WT-rep2, daptomycin treated samples were labeled with Alexa Fluor 647 and untreated samples with Alexa Fluor 555. For WT-rep3, the daptomycin treated sample was labeled with Alexa Fluor 555 and the untreated sample with Alexa Fluor 647.
Project description:Daptomycin is a lipopeptide antibiotic that has recently been approved for treatment of Gram-positive bacterial infections. The mode of action of daptomycin is not yet entirely clear. To further understand the mechanism transcriptomic analysis of changes in gene expression in daptomycin-treated Staphylococcus aureus was carried out. The expression profile indicated that cell wall stress stimulon member genes (B. J. Wilkinson, A. Muthaiyan, and R. K. Jayaswal. 2005. Curr. Med. Chem. Anti-Infective Agents 4: 259-276) were significantly induced by daptomycin, and by the cell wall-active antibiotics vancomycin and oxacillin. Comparison of the daptomycin response of a two-component cell wall stress stimulon regulator VraSR mutant, S. aureus KVR, to its parent N315 showed diminished expression of the cell wall stress stimulon in the mutant. Daptomycin has been proposed to cause membrane depolarization, and the transcriptional responses to carbonyl cyanide m-chlorophenylhydrazone (CCCP) and nisin were determined. Transcriptional profiles of the responses to these antimicrobial agents showed significantly different patterns compared to those of the cell wall-active antibiotics, including little or no induction of the cell wall stress stimulon. However, there were a significant number of genes induced by both CCCP and daptomycin that were not induced by oxacillin or vancomycin, such that the daptomycin transcriptome was probably reflecting a membrane depolarizing activity of this antimicrobial also. The results indicate that inhibition of peptidoglycan biosynthesis, either directly or indirectly, and membrane depolarization are parts of the mode of action of daptomycin. Keywords: mode of action, transcriptional profiling
Project description:Abstract of associated manuscript: Daptomycin is the first of a new class of cyclic lipopeptide antibiotics used against multidrug-resistant Gram-positive pathogens. The proposed mechanism of action involves disruption of the functional integrity of the bacterial membrane in a Ca2+-dependent manner. We have used transcriptional profiling to demonstrate that treatment of Bacillus subtilis with daptomycin strongly induces the lia operon including the autoregulatory LiaRS two-component system (homologous to Staphylococcus aureus VraSR). The lia operon protects against daptomycin and deletion of liaH, encoding a phage shock protein A (PspA)-like protein, leads to 3-fold increased susceptibility. Since daptomycin interacts with the membrane, we tested mutants with altered membrane composition for effects on susceptibility. Deletion mutations of mprF (lacking lysyl-phosphatidylglycerol) or des (lipid desaturase) increased daptomycin susceptibility, whereas overexpression of MprF decreased susceptibility. Conversely, depletion of the cell for the anionic lipid phosphatidylglycerol led to increased resistance. Fluorescently-labeled daptomycin localized to the septa and in a helical pattern around the cell envelope and was delocalized upon depletion of phosphatidylglycerol. Together, these results indicate that the daptomycin-Ca2+ complex interacts preferentially with regions enriched in anionic phospholipids and leads to membrane stresses that can be ameliorated by PspA family proteins.