It’s a dog-eat-dog world in the microbial environment, with bacteria fighting pitched battles between each other for environmental dominance. And one of the weapons of choice is surprisingly valuable to food safety: bacteriocins from lactic acid bacteria (LABs).
Bacteriocins are heat-stable, anti-microbial peptides synthesized by ribosomes in many bacterial species. These small proteins, less than 10 kDa in size, disable and kill competing strains, often by inducing rapid pore formation in outer membranes so the cell literally leaks to death. Produced as primary metabolites by their host cell, bacteriocins are extremely amenable to biosynthetic production. They therefore receive a lot of attention from both the food and pharmaceutical industries. Perez et al. (2014) provide an introduction and review to bacteriocin discovery and characterization, with specific focus on food applications using LABs that are generally recognized as safe (GRAS).1
LABs have a long association with foodstuff, since their fermentation properties make them attractive nutritionally. Across the globe, people have used LABs to ferment food and thereby influence nutritional quality and aesthetic factors such as taste and aroma, and to prolong storage. Due to this historical association, the United States Food and Drug Administration (FDA) considers LABs to be GRAS for inclusion in food production. This makes them ideal candidates for further investigation as food preservatives, in addition to their pharmaceutical potential as next-generation antibiotics.
Researchers categorize bacteriocins into two classes, I and II, with the latter further subdivided into four groupings according to structure. This structure determines stability, specificity and activity.
- Class I, or lantibiotic bacteriocins, are peptides smaller than 5 kDa with extensive post-translational residue modification that contributes to their characteristic ring structure and activity. This class includes nisin A; at the time of review by Perez et al., nisins were the only commercially available bacteriocins for food use. Their long association with food sets a useful precedent for developing new bacteriocins in the food industry.
- Class II, or non-lanthionine-containing bacteriocins, are produced by a wide variety of bacterial species. These 5 to 10 kDa peptides do not undergo extensive post-translational modification as is seen with class I bacteriocins.
Both classes show a number of beneficial properties that make them ideal for food use as well as candidates for pharmaceutical development:
- thermotolerant over a broad range and generally resistant to thermal stress
- active over a wide pH range
- colorless, odorless and tasteless
- active and effective even at low concentrations
- easily degraded by proteolysis in the gut
Furthermore, there is no documented development of microbial resistance, which makes bacteriocins strong candidates for treating multiple-drug-resistant infections.
Since they are primary metabolites, bacteriocins are also extremely attractive for biosynthesis, since bioengineering can easily increase activity and specificity for scalable production.
As GRAS microbes, LABs show potential as food biopreservatives, either as sole agents or in combination with other approaches. Moreover, they exhibit strong anti-microbial activity against Listeria monocytogenes, performing well in adverse food conditions where other measures often fail.
For the food industry, several different approaches exist:
- Direct application: Producers add bacteriocin directly to product.
- Culture: Producers encourage bacteriocin-producing LAB growth in product itself.
- Fermentation: Producers exploit natural LAB fermentation for preservation.
- Packaging: Producers incorporate bacteriocins into biocomposite packaging materials to surround foods.
Bacteriocins also show potential in the food processing environment: nisin-containing hand gels aid worker hygiene to decrease spread of spoilage and foodborne disease (FBD) pathogens. Bacteriocins are also available as veterinary drugs to treat bovine mastitis.
As consumer preference switches to non-chemical alternatives for food preservation, LAB-derived bacteriocins show great potential in the food industry. Their anti-microbial actions against food spoilage organisms prolong shelf life and reduce food waste, in addition to eliminating FBD pathogens. As GRAS food-grade bacteria, LABs could be a valuable tool for food producers.
1. Perez, R.H. et al. (2014) “Novel bacteriocins from lactic acid bacteria (LAB): various structures and applications.” Microbial Cell Factories 13(Suppl 1) (p. S3).