Introduction: Pseudomonas aeruginosa employs several strategies to tolerate the effects of a broad range of antibiotics including possession of a highly impermeable outer-membrane (OM) and multi-drug efflux pumps. We have recently shown that P. aeruginosa tolerates β-lactam antibiotics by undergoing a rapid en masse conversion from bacilli to cell wall deficient (CWD) forms that lack the OM [1]. We hypothesized that CWD P. aeruginosa may be susceptible to antibacterial compounds that are normally inhibited by the Gram-negative cell wall.
Methods: We found that β-lactam-induced CWD P. aeruginosa is rapidly killed by antimicrobial peptides (AMPs), that are normally ineffective against bacillary P. aeruginosa [1]. These observations suggest that β-lactam antibiotics in combination with compounds that exploit the susceptibility of CWD may be novel therapeutic options. However, the increasing prevalence of β-lactam resistance in clinical settings has created a need to develop novel drugs that induce the transition to the CWD form for this strategy to be effective. The redox indicator resazurin was used to track cell growth using a fluorescence plate reader. Screens were performed in a 96 well plate format to allow for high throughput screening and validated using meropenem and nisin to induce and kill CWD P. aeruginosa.
Results: We have developed simple, cheap high throughput screening methods that will enable the development of novel therapeutic approaches that exploit the susceptibility of CWD P. aeruginosa.
Conclusion: These high throughput screening methods can be used as drug discovery tools to develop novel therapeutic options against P. aeruginosa.
References:
1. Monahan, L.G., Turnbull, L., Osvath, S.R., Birch, D., Charles, I.G. and Whitchurch, C.B., Rapid Conversion of Pseudomonas aeruginosa to a Spherical Cell Morphotype
Facilitates Tolerance to Carbapenems and Penicillins but Increases Susceptibility to Antimicrobial Peptides. Antimicrobial Agents and Chemotherapy, 2014. 58: p. 1956-1962.