Hoisted by Their Own Petard: Defeating Immunity Protein-Mediated Bacteriocin Resistance

The irresponsible use of antibiotics has led to an erratic spread of antimicrobial resistance (AMR) among bacterial pathogens. Without intervention, 10 million AMR-related deaths per year by 2050 are estimated by the WHO. Nonetheless, the development of novel antibiotics has almost come to a halt. In this context, naturally occurring narrow-spectrum antimicrobial proteins, known as bacteriocins, are promising alternatives to address the need for effective and selective antimicrobial treatments. However, the widespread distribution of cognate immunity proteins among bacteriocin producers vastly limits the natural antimicrobial spectrum against Gram-negative bacteria. On the example of pyocin S2 (PyoS2), an S-type HNH DNase bacteriocin targeting the opportunistic human pathogen Pseudomonas aeruginosa, this study demonstrates for the first time that a rationally introduced single mutation and chemical protein functionalisation at PyoS2s immunity protein exosite fully eradicate immunity protein-mediated resistance to pyocins in multidrug-resistant clinical P. aeruginosa isolates. The presented findings highlight a strategy to engineer bacteriocins from pathogenic Gram-negative bacteria with an extended antimicrobial spectrum, overruling the prevalent and predominant bacteriocin resistance mechanism of immunity protein binding. This strategy could expedite the development of engineered bacteriocins to expand our repository of antimicrobials to combat the worsening antimicrobial resistance crisis and avert a post-antibiotic era.