An essential protease, FtsH, influences daptomycin resistance acquisition in Enterococcus faecalis

Daptomycin is a last-line antibiotic commonly used to treat vancomycin-resistant Enterococci, but resistance evolves rapidly and further restricts already limited treatment options. While genetic determinants associated with clinical daptomycin resistance (DAPR) have been described, information on factors affecting the speed of DAPR acquisition is limited. The multiple peptide resistance factor (MprF), a phosphatidylglycerol-modifying enzyme involved in cationic antimicrobial resistance, is linked to DAPR in pathogens such as methicillin-resistant Staphylococcus aureus. Since Enterococcus faecalis encodes two paralogs of mprF and clinical DAPR mutations do not map to mprF, we hypothesized that functional redundancy between the paralogs prevents mprF-mediated resistance and masks other evolutionary pathways to DAPR. Here, we performed in vitro evolution to DAPR in mprF mutant background. We discovered that the absence of mprF results in slowed DAPR evolution and is associated with inactivating mutations in ftsH, resulting in the depletion of the chaperone repressor HrcA. We also report that ftsH is essential in the parental, but not in the ΔmprF, strain where FtsH depletion results in growth impairment in the parental strain, a phenotype associated with reduced extracellular acidification and reduced ability for metabolic reduction. This presents FtsH and HrcA as enticing targets for developing anti-resistance strategies.

Role of HrcA in stress management in Mycobacterium tuberculosis

AIM

The current study aims to understand the role of HrcA in stress response of M. tuberculosis.

METHODS AND RESULTS

In this study, using an hrcA knock out mutant of M. tuberculosis it is demonstrated that the heat shock repressor, HrcA is important for countering environmental stresses pathogen faces within the host during the infection process. Also, with scanning electron microscopy it has been shown that HrcA plays a role in maintaining the morphology and cell size of the pathogen as disruption of the hrcA gene resulted in significantly elongated bacilli. Further, heat shock proteins like ClpC1, ClpB, DnaK, GroEL2, GroEL1, DnaJ2 and GroES were detected in the secretome of M. tuberculosis by mass spectrometric analysis. The study also demonstrates a strong humoral response against M. tuberculosis heat shock proteins in H₃₇ R_v infected mice sera.

CONCLUSION

The study establishes that though hrcA is not an essential gene for M. tuberculosis, it regulates the expression of heat shock proteins during infection, and disruption of hrcA gives a survival advantage to the pathogen during stress conditions.

SIGNIFICANCE

and Impact of the Study: HrcA plays an important role in maintaining a fine balance of heat shock proteins during infection to give adequate survival advantage and also evade immune detection.