Food safety testing with probiotics

This Q&A explains why probiotics in food products impacts contamination testing and suggests ways to negate the problem.

Can you discuss the specific microbial contaminants of concern that are typically encountered in probiotic products? How do these contaminants differ from those in other types of food products?

Food pathogens remain the greatest concern for any food product: Salmonella, Listeria, and E. coli. These contaminants don’t necessarily differ from other food items, but probiotics can interfere with the pathogen testing methods used to detect them. Other general indicator organisms like Staphylococcus aureus, Bacillus cereus, moulds and yeasts, and Enterobacteriaceae should also be tested to show good hygienic conditions were maintained during manufacture. Pseudomonas aeruginosa is also another good indicator to show if contaminated water or soil has entered the production environment at some point. 

Probiotic products contain live microorganisms, which could potentially interfere with the accurate detection of target organisms. Could you elaborate on how these probiotics might impact the detection process? What strategies can be employed to minimise this interference?

Probiotic bacteria include lactic acid bacteria (Lactobacillus, Lactococcus, Pediococcus, Streptococcus, Enterococcus), Bacillus (B. coagulans, B. subtilis), several species of Bifidobacterium, and the yeast Saccharomyces (S. cerevisiae var. boulardi., S. boulardii). While conferring health benefits to the consumer, probiotics have been known to produce antimicrobial compounds that can interfere with detection of pathogens or hygiene indicators. These can include organic acids, bacteriocins, hydrogen peroxide, lipopeptides, and possibly other compounds that have yet to be determined. 

During testing, probiotics will also compete for nutrient resources against the target contaminants. This competition, in addition to the production of antimicrobial compounds, will either kill or prevent the target organisms from growing to a concentration that will be successfully detected.

To mitigate probiotic interference, several strategies may be employed to improve detection of the target organism. For example, increasing the enrichment dilution of the sample (ie, 1:100, 1:200) provides more buffering and nutrients for the target organism to grow and dilutes any antimicrobial compounds produced. However, a higher enrichment dilution will decrease the sensitivity of the method. Alternatively, the use of a medium with increased buffering capacity (ie, double-strength buffered peptone water) may help negate the effect of acid produced by the probiotics. Also, supplementing the enrichment media with antibiotics (ie, vancomycin, novobiocin, mupirocin) can also suppress the growth of the probiotics in the enrichment. Care must be taken to select the appropriate antibiotic that will ensure inhibition of the probiotic strains and allow the target organism to grow. Regardless of which strategy is employed, verification of the chosen strategy must be performed to demonstrate successful detection of the target organism in the presence of probiotics.