One light to rule them all: photodynamic inactivation of diverse Campylobacter

Campylobacter , the leading cause of bacterial gastroenteritis worldwide, routinely contaminates UK poultry products, often destined for the kitchens of the general public who risk infection through improper handling. Alongside rising antimicrobial resistance (AMR), the sheer abundance of Campylobacter in the food chain is undermining current intervention strategies. A novel approach to reduce surface contamination on poultry products is violet-blue photodynamic inactivation (VB-PDI), which uses 405 nm visible light to activate endogenous photosensitizers and generate bactericidal intracellular levels of reactive oxygen species. We previously demonstrated VB-PDI is effective against reference strains of Campylobacter jejuni and determined the molecular underpinnings in detail. However, the cross-species efficacy, resistance potential and performance against AMR isolates remained uncharacterized. Here, we evaluate VB-PDI efficacy against 64 Campylobacter field isolates from UK poultry surveillance programmes, comprising three Campylobacter species of various antibiotic resistance profiles. All isolates were susceptible to VB-PDI to a similar level, demonstrating broad efficacy irrespective of species or phenotype. In vitro evolution assays did not result in any detectable increase in VB-PDI tolerance after fifteen repeat exposures which, together with the lack of any notably resistant isolates in our broad screen, indicates the risk of intrinsic or evolved resistance is minimal. Consequently, VB-PDI offers a promising and robust intervention strategy for reducing Campylobacter in the food chain, and here we discuss possible modes of implementation.