In search of new antibiotics that exploit the cell wall deficient L-form lifestyle

Max DO, Lazenby JJ and Whitchurch CB

The ithree institute, University of Technology Sydney, Ultimo, NSW, Australia.

Pseudomonas aeruginosa is a Gram negative bacterial pathogen that has been identified by the WHO as in critical need for the development of new antibiotics. P. aeruginosa has high levels of intrinsic resistance to a broad range of antibiotics due to possession of a highly impermeant outer-membrane (OM) and multiple, inducible multi-drug efflux pumps. We have previously shown that P. aeruginosa tolerates β-lactam antibiotics by undergoing a rapid and reversible en masse conversion from bacilli to cell wall deficient L-forms that lack the OM. We hypothesized that L-form P. aeruginosa may be susceptible to antibacterial compounds that are normally inhibited by the Gram negative cell wall. Indeed we found that L-form P. aeruginosa is rapidly killed by antimicrobial peptides (AMPs) that are normally ineffective against bacillary P. aeruginosa. These observations suggest that drug combinations that induce L-form transitions with compounds that exploit L-form susceptibility may be novel therapeutic options. We have developed high-throughput screens that enable the identification of compounds that induce or kill L-form bacteria. We have used our L-form kill assay to screen an FDA-approved drug library and have identified ~100 drugs with enhanced bactericidal activity against L-form P. aeruginosa. Interestingly, most of these drugs have not previously been identified as having any antibiotic activity indicating that there are a number of FDA-approved drugs that might be able to be repurposed for use as antibiotic therapeutics that target L-form bacteria. Our observations indicate that the ability of bacteria to transition into CWD deficient L-form lifestyle to avoid the effect of compounds that target the bacterial cell wall may be exploited to develop novel antibiotic therapeutic approaches.