Sampling and testing for pathogens in food: finding the needle in a haystack and the impact of the food microbiome

Microbiological testing provides food businesses and competent governmental authorities reference points to verify that food safety measures are well implemented. For pathogens, often absence testing is required in one or in several samples of 25 g of food; hence, the test procedure should be able to detect extremely low concentrations of cells. To date, direct detection of these low levels of contaminants is not possible, and adequate detection relies on an enrichment step to increase cell concentrations to detectable levels. The detection chance of pathogens is influenced by intrinsic and extrinsic factors such as an uneven distribution of cells in a food batch, the physiological status of the cells, intraspecies and intrastrain variability, specific food components, and the food microbiome. The advantages and disadvantages of nonselective and selective enrichments are discussed, as well as molecular detection procedures to detect single and multiple pathogens from the food they reside in. • Absence in all test samples does not mean pathogen levels in a batch are negligible. • An enrichment step is needed to detect one bacterial cell per 25 g of food. • Careful determining detection limits of methods critical for detection efficacy.