Oxygen limitation induces acid tolerance and impacts simulated gastro-intestinal transit in Listeria monocytogenes J0161

Listeria monocytogenes is a food-borne pathogen and the causative agent of listeriosis, a severe infection to those with a pre-disposition. Infections often arise through consumption of contaminated foods, where high intrinsic resistance to food processing practises permit survival and growth. Several practises, including refrigeration, acidification and oxygen limitation are ineffective in controlling L. monocytogenes, therefore foods which do not undergo thermal processing, e.g. ready-to-eat products, are considered high risk. While the responses to several food processing practises have been investigated, there are few reports on the responses of L. monocytogenes to oxygen limitation. Therefore the aim of this study was to investigate the effects of oxygen limitation on stress response and survival capacity during simulated gastro-intestinal transit. Findings: Anaerobiosis induced an acid tolerance response, causing cells to be more resistant to organic and inorganic acids than aerobically grown counterparts (p < 0.05). Using a gastro-intestinal transit model it was found that anaerobic growth induced an acid tolerance response which enhanced resistance to pH 2.5 simulated gastric juice (SGJ) compared to aerobically grown cells (p < 0.05). This response was most pronounced in exponential phase cells. However, exposure of stationary phase cells to pH 3.5 SGJ enhanced bile tolerance, suggesting a link between acid and bile tolerance. Conclusions: The responses of L. monocytogenes to oxygen limitation are not extensively studied. These findings provide an initial insight into the effects of anaerobiosis on stress response and survival potential in L. monocytogenes. While it appears anaerobiosis may impact these, further work is required to confirm these findings are not strain specific.