Reversal of carbapenem resistance in Pseudomonas aeruginosa by camelid single domain antibody fragment (VHH) against the C4 dicarboxylate transporter

The COVID-19 pandemic has hastened the problem of nosocomial drug-resistant pathogens and is exerting a huge toll on hospitalized patients in critical care settings. Most small molecule antibiotics are susceptible to bacterial resistance mechanisms and constantly becoming ineffective leading to rapid shrinkage of the antibiotic armamentarium. Pseudomonas aeruginosa, one of the most common pathogens in hospital-born infection and considered critically dangerous by WHO and CDC, is extremely difficult to treat with frontline drugs, the carbapenems. In this study, we developed a camelid antibody fragment (VHH) library against whole P. aeruginosa and isolated a highly potent neutralizing hit (PsC23) that selectively targets P. aeruginosa . At 25 {micro}g/mL, PsC23 inhibited growth of the ATCC 27853 and a locally isolated carbapenem resistant MCC 50428 P. aeruginosa. The target of PsC23 is the C4 dicarboxylate transporter that transports C4 metabolites to the glyoxylate shunt during oxidative stress that is present in pathogens but not the human host. This ultimately results in the blockade of the shunt affecting bacterial energy transduction that leads to disruption of drug efflux. Interestingly, in a neutropenic mouse with MCC 50428 systemic infection, PsC23 in combination with meropenem completely reversed the drug resistance and eliminated the pathogens from the blood. PsC23 was stable in human serum and had no hemolytic or cytotoxic effect on human cells. Taken together, this VHH if co administered with the currently available carbapenems would reverse carbapenem resistance and could be used to effectively control P. aeruginosa in critical care settings.