Violet-blue light kills all 64 Campylobacter strains from UK poultry in Reading lab tests

The strength of the design is the panel of 64 isolates. The strains came from the Animal and Plant Health Agency's surveillance programme, so the test covered the range of Campylobacter actually circulating in UK poultry, beyond laboratory reference strains ^[11]. A study on one or two reference strains could not show whether a wild multidrug-resistant isolate would survive the light. This one could. "We've shown it works against a wide range of real-world strains taken directly from U.K. poultry, including the multidrug-resistant strains that worry us most, and we can't find any evidence that resistance could evolve," said Dr Aidan Taylor of the University of Reading, the lead author ^[4].

The thing this doesn't tell you is the size of the kill. The phys.org account of the Microbiology paper ^[2] does not give the light dose, the exposure time or the fraction of bacteria left alive. A processing plant would need those figures to judge whether the step fits a line. A dead culture in a lab is also a different result from a clean carcass. Dr Samuel Connelly of the Animal and Plant Health Agency, who co-led the research, said: "While further evaluation using contaminated meat samples is required, the simplicity and adaptability of this technology suggest that it could be implemented at various stages of the food production process." ^[12]

Taylor rests the durability claim on the chemical-free design. "What's exciting about this light-based approach is that it doesn't rely on chemicals or antibiotics at all, so it sidesteps the resistance problem entirely," he said ^[7]. The experimental support is a forced-evolution run on a single strain, and 15 rounds produced no rise in tolerance ^[1]. That shows tolerance did not emerge under those conditions. A longer run across several strains would be the stronger test.

Cooking kills Campylobacter, and cross-contamination from handling raw meat is thought to be the main route of infection ^[10]. The bacterial load on raw carcasses is what a processing step can change. The team's retail estimate, from about 1 in 10 highly contaminated carcasses to 1 in 50 ^[9], is a fivefold fall, from 10% to 2% of carcasses ^[15][16]. It assumes a 100-fold cut in contamination that no meat trial has yet measured.

The comparison with chlorine comes from earlier research that found blue light could work better than chlorine against specific strains ^[13]. This study tested the light alone. In my view the new paper makes violet-blue light a credible candidate for a post-slaughter carcass step ^[8]. That holds on one condition: the meat trials have to show a large kill at a dose a line can deliver. The bacterium causes hundreds of thousands of UK cases a year, at an estimated cost of 700 million pounds in health care and lost productivity ^[6].