The opportunistic human pathogen Staphylococcus aureus can evade antibiotics by acquiring antibiotic resistance genes or by entering into a non-growing dormant state. Moreover, the particular circumstances of a specific infection site, such as acidity or anaerobicity, often weaken antibiotic potency. Decreased bacterial susceptibility combined with diminished antibiotic potency is responsible for high failure rates when treating S. aureus infections. Here, we report that the membrane-active antimicrobial agent nTZDpa does not only exhibit enhanced antibiotic activity against multidrug-resistant Gram-positive pathogens in acidic pH, but also retains antimicrobial potency under anaerobic conditions. This agent completely eradicated highly antibiotic-tolerant cells and biofilms formed by methicillin-resistant S. aureus at pH 5.5 at concentrations at which it was not potent at pH 7.4. Furthermore, nTZDpa was more potent at synergistically potentiating gentamicin killing against antibiotic-tolerant MRSA cells at low pH than at high pH. All-atom molecular dynamics simulations combined with membrane-permeabilization assays revealed that the neutral form of nTZDpa, which contains carboxylic acid, is more effective than the deprotonated form at penetrating the bacterial membrane and plays an essential role in membrane activity. An acidic pH increases the proportion of the neutrally charged nTZDpa, which results in antimicrobial enhancement. Our results provide key insights into rational design of pH-sensitive membrane-active antimicrobials and antibiotic adjuvants that are effective in an infection environment. These findings demonstrate that nTZDpa is a promising lead compound for developing new therapeutics against hard-to-cure infections caused by drug-resistant and -tolerant S. aureus.
Bibliographical noteFunding Information:
This study was supported by the National Research Foundation of Korea (NRF) Grant ( 2020R1C1C1008842 , 2018R1A5A2025286 ) and Korea Medical Device Development Fund grant ( KMDF_PR_20200901_0073 ). J.K. was supported by by the Research Program to Solve Social Issues of NRF of Korea ( 2017M3A9E4077234 ). F.M.A. and E.M. were supported by National Institutes of Health Grant P01AI083214 . H.G. acknowledges support from the Singapore Ministry of Education ( MOE ) AcRF Tier 1 (Grants RG138/20 ). G. Z. and H. G. acknowledge a start-up grant from Nanyang Technological University and the Agency for Science, Technology and Research (A*STAR), Singapore. Experimental equipment was supported by Korea Basic Science Institute ( National research Facilities and Equipment Center ) grant ( 2021R1A6C101A442 ). The MD simulations reported were performed using resources of the National Supercomputing Centre , Singapore ( http://www.nscc.sg ).
- C. elegans
- Infection environment
- Membrane-active agent