Project description:Regulatory RNAs (sRNAs) are now considered as major players in many physiological and adaptive responses in pathogenic bacteria. sRNAs have been extensively studied in Gram-negative bacteria, but less information is available in Gram-positive pathogens. There is a spread of multidrug-resistant (MDR) opportunistic organisms, grouped as “ESKAPE” pathogens, which comprise enterococci, a leading cause of hospital-acquired infections and outbreaks with emergence of MDR isolates, especially vancomycin-resistant Enterococcus faecium (VREF). Note that no information about sRNA expression is known in this major opportunistic pathogen. By transcriptomic and genomic analyses using E. faecium Aus0004 reference strain, 249 transcribed IGRs, including sRNA candidates, were detected and, using a series of cut-offs, this set was lowered down to 54 sRNAs while 7 that were predicted based on comparative sequence analysis. RNA-seq was performed with and without subinhibitory concentrations (SIC) of daptomycin, a cyclic lipopeptide antibiotic used for VREF infections. Under daptomycin SIC exposure, 260 genes (9.1% of the genome) had a significant alteration of expression including 80 upregulated genes and 180 downregulated genes. Among the repressed genes, a large proportion (55%) coded for proteins involved in carbohydrate and transport metabolism. Also, we focused on the 9 sRNAs exhibiting the highest expression, and all of them were confirmed as expressed along bacterial growth by Northern blots and qPCR. Out of these 9 sRNAs, four had significantly lower or higher expression in the presence of daptomycin SIC, and therefore responded to antibiotic exposure. Finally, we also tested the expression of these 9 sRNAs in a collection of isogenic Aus0004 mutants with increasing levels of daptomycin resistance, and we observed by qPCR that some sRNAs had a significantly modified expression in daptomycin resistance mutants. It highlights the significant implication of some of the E. faecium sRNAs in the early steps of the development of daptomycin resistance. This is the first experimental genome-wide sRNA identification in Gram-positive E. faecium, a leading cause of hospital acquired infections. Overall design: Identification of the first sRNAs in Enterococcus faecium and transcriptome analysis by RNA-seq to monitor the levels of all transcripts (mRNAs and sRNAs) in bacterial cells grown in the absence or the presence of a subinhibitory concentration (0.5 mg/L) of daptomycin
Project description:Enterococcus faecium has become a major opportunistic pathogen with the emergence of multidrug-resistant clones that are well-adapted to the hospital environment. As part of the vast diversity of gut microbiota, they are faced with different environmental stress, including antimicrobial pressure. By contrast, little is known about the effect of non-antibiotic molecules on bacterial physiology while numerous drugs are used in inpatients, especially those hospitalized in intensive care units (ICUs). The aim of this study was to investigate the impact of the most prescribed xenobiotics in ICUs on fitness, pathogenicity and antimicrobial resistance of E. faecium. Several phenotypic analysis was carried out and we rapidly brought to light that caspofungin, an antifungal agent belonging to the echinocandin family, seemed to have an important impact on E. faecium growth. Since the fungal target of caspofungin [beta-(1,3)-glucan synthase] is absent in enterococci, the mechanism of caspofungin action was investigated by several approaches. First, we decided to confirm this result by electronic microscopy and a peptidoglycan analysis by Ultra Performance Liquid Chromatography coupled with mass spectrometry (UPLC-MS/MS). Again, we highlighted that caspofungin even at subinhibitory concentrations (SICs) seemed to have an impact on cell wall organization especially in muropeptide precursors abundance. Then, a transcriptomic analysis was performed by RNA-seq (HiSeq 2500, Illumina) using the vanB-positive reference strain E. faecium Aus0004 in the presence or absence of caspofungin SIC (8 mg/L i.e., ¼ of the MIC). Transcriptomic analysis showed that the expression of 568 genes (19.9% of the genome) was significantly altered in the presence of caspofungin SIC, with 323 genes induced (fold change >2, p-value <0.1) and 245 genes repressed (fold change <-2, p-value <0.1). Regarding the repressed genes, the pdhABCD operon is largely downregulated (fold changes -4.3, -9.7, -6.9 and -6.4, respectively). This operon encoded components of the pyruvate deshydrogenase multienzyme complex involved in bacterial energetic pathway by the citrate cycle (i.e., TCA cycle). Moreover, it seemed that the glycerol metabolism pathway and in particular the glpOKF operon is downregulated too. The dramatic alteration of TCA seemed to have an drastic impact on bacterial cells viability indeed decrease of glycerol metabolism could explain the conformational modifications of peptidoglycan. Overall design: Transcriptome analysis by RNA-seq to monitor the levels of all transcripts in bacterial cells grown in the absence or the presence of a subinhibitory concentration (8 mg/L) of caspofungin
Project description:Teixobactin is the first novel antimicrobial to be discovered in decades and represents a new class of antimicrobials. Teixobactin shows great promise with proven efficacy against multi-drug resistant organisms such as methicillin-resistant S. aureus (MRSA), vancomycin-resistant Enterococci (VRE), and Mycobacterium tuberculosis. VRE infections are notoriously difficult to treat with complex and adaptable cell wall stress response systems, which confer intrinsic resistance to a wide variety of antimicrobials. The aim of this study was to isolate the teixobactin-induced transcriptional response by challenging lab strain Enterococcus faecalis JH2-2 with sub-MIC levels of teixobactin using RNA sequencing. Two cultures of E. faecalis were grown to an OD600 of 0.2 and subsequently split into three to form a total of six cultures (two samples, with three technical replicates each), and grown to an OD600 of 0.5. One set of three cultures were treated with 0.5 ug/ml (0.25 x MIC), and all six cultures were grown for a further 1h. Cells were harvested by centrifugation and stored at -80 degrees C. RNA was extracted using TRIzol-chloroform and RNA samples were run through the RNAeasy Minikit (Qiagen). The Agilent RNA 6000 Nano kit and the Agilent 2100 Bioanalyzer (RIN >8), was used to verify RNA quality as per the manufacturer’s instructions, and RNA concentration was determined using a NanoDrop ND-100 spectrophotometer. Ribosomal RNA was removed from total RNA using Ribo-Zero and cDNA libraries were created using the Illumina TruSeq™ stranded total RNA library prep kit. Sequencing was completed using Illumina MiSeq_v3 generating 150 bp single end reads. Adapter sequences were removed from raw fastq files using Flexbar and reads shorter than 50bp were discarded. Sequence reads from each sample were mapped against the E. faecalis JH2-2 genome (NZ_KI518257.1) using Bowtie to produce a table of raw read counts for JH2-2 genes for each of the replicates. Statistical and principal component analysis were performed using the Bioconductor DESeq package.