Genomewide Profiling of the Enterococcus faecalis Transcriptional Response to Teixobactin Reveals CroRS as an Essential Regulator of Antimicrobial Tolerance

Abstract

Teixobactin is a new antimicrobial of significant interest. It is active against a number of multidrug-resistant pathogens, including Staphylococcus aureus and Enterococcus faecalis, with no reported mechanisms of teixobactin resistance. However, historically, mechanisms of resistance always exist and arise upon introduction of a new antimicrobial into a clinical setting. Therefore, for teixobactin to remain effective long term, we need to understand how mechanisms of resistance could develop. Here we demonstrate that E. faecalis shows a remarkable intrinsic tolerance to high concentrations of teixobactin. This is of critical importance, as antimicrobial tolerance has been shown to precede the development of antimicrobial resistance. To identify potential pathways responsible for this tolerance, we determined the genomewide expression profile of E. faecalis strain JH2-2 in response to teixobactin using RNA sequencing. A total of 573 genes were differentially expressed (2.0-fold log2 change in expression) in response to teixobactin, with genes involved in cell wall biogenesis and division and transport/binding being among those that were the most upregulated. Comparative analyses of E. faecalis cell wall-targeting antimicrobial transcriptomes identified CroRS, LiaRS, and YclRK to be important two-component regulators of antimicrobial-mediated stress. Further investigation of CroRS demonstrated that deletion of croRS abolished tolerance to teixobactin and to other cell wall-targeting antimicrobials. This highlights the crucial role of CroRS in controlling the molecular response to teixobactin. IMPORTANCE Teixobactin is a new antimicrobial with no known mechanisms of resistance. Understanding how resistance could develop will be crucial to the success and longevity of teixobactin as a new potent antimicrobial. Antimicrobial tolerance has been shown to facilitate the development of resistance, and we show that E. faecalis is intrinsically tolerant to teixobactin at high concentrations. We subsequently chose E. faecalis as a model to elucidate the molecular mechanism underpinning teixobactin tolerance and how this may contribute to the development of teixobactin resistance.

Antimicrobial Resistance and Its Spread Is a Global Threat

“…Teixobactin, a new antimicrobial agent has documented activity against S. aureus and Enterococcus faecalis without resistance. A study which reported on the transcriptional response of E. faecalis to teixobactin levels identified development of intrinsic tolerance to high concentrations of the same (through deletion of croRS ), and this is generally considered a precursor for the development of resistance [ 70 ]. Besides known mechanisms, involving differential expression of genes targeted by antibiotics, and xenobiotic efflux transporters, emerging studies have the potential to reveal regulatory circuits that respond to different toxic stimuli and other compensatory mechanisms.…”

Antimicrobial Effects of L-Chg10-Teixobactin against Enterococcus faecalis In Vitro

“…MIC is defined as the lowest concentration required for the antibacterial agents to inhibit ≥90% of bacterial growth [23,24]. In this study, the MIC value of L -Chg 10 -teixobactin on E. faecalis ATCC 29212 and ATCC 47077 strains was lower than the 2 µg/mL reported by Darnell et al [25] on a different strain of E. faecalis, i.e., strain JH2-2; it was slightly higher than the 0.5 µg/mL reported by Ling et al [16] on vancomycin-resistant E. faecalis [16,25]. Two plausible explanations may account for the differences, including the use of different teixobactin or its analogues as the tested drug and the different strains of E. faecalis studied.…”

IreK-Mediated, Cell Wall-Protective Phosphorylation in Enterococcus faecalis

“…62,63 Previous E. faecalis transcriptome studies display a downregulation of ribosomal proteins when cell wall synthesis is inhibited following antimicrobial treatment. 64,65 In the global proteome data analyzed here, proteins related with translation are decreased in abundance specifically after ceftriaxone treatment (which inhibits cell wall synthesis by preventing cross-linking of peptidoglycan outside the cytoplasmic membrane) and this could result in the production of incomplete proteins in the cytoplasm for processing by SsrA/ SmpB. These results suggest that this quality control and degradation pathway is controlled through phosphorylation.…”