Gut Bacteria Weaponized Against Superbugs Threatening the Food Supply

A quiet arms race is unfolding inside fermented foods, and a new study suggests the good guys are winning. Researchers evaluating five commercially important strains of lactic acid bacteria have found that these microbes, long prized for turning milk into yogurt and cabbage into sauerkraut, are also prolific manufacturers of natural antimicrobial weapons capable of devastating some of the most dangerous foodborne pathogens on the planet. At a time when multidrug-resistant bacteria are rendering conventional antibiotics and chemical preservatives increasingly ineffective, the findings offer a tantalizing glimpse of a future where the preservatives in our food are grown, not synthesized in a chemical plant.

The research, published in the journal MicrobiologyOpen, focused on five strains with established probiotic credentials: Lactiplantibacillus plantarum NBRC 3070, Lactobacillus acidophilus ATCC 4356, Lacticaseibacillus casei ATCC 393, Lacticaseibacillus rhamnosus GG ATCC 53103, and Bifidobacterium animalis subsp. lactis ATCC 27673. These are not obscure laboratory curiosities. They are workhorse organisms used in food fermentation and probiotic formulations worldwide, which means that any antimicrobial compounds they produce could, in principle, be translated into industrial biopreservation strategies with relative speed. The team pitted both the live bacteria and their cell-free metabolites against a panel of seven indicator pathogens, including Escherichia coli, Salmonella enterica serovar Typhimurium, Staphylococcus aureus, Shigella sonnei, Pseudomonas aeruginosa, Serratia marcescens, and Bacillus cereus, organisms routinely implicated in contamination of meat, dairy, water, and ready-to-eat foods.

The results were striking. When whole bacterial cultures of the lactic acid bacteria were tested using agar well diffusion, inhibition zones ranged from roughly 15 to 23 millimeters, placing most of the target pathogens in the very sensitive to extremely sensitive categories. Lactiplantibacillus plantarum NBRC 3070 emerged as a standout performer, producing the largest average inhibition zones, while E. coli ATCC 25922 proved the most vulnerable target overall, with a mean inhibition zone exceeding 21 millimeters across all five producer strains. Shigella sonnei, by contrast, showed the greatest resilience, a reminder that even nature’s antimicrobials face pathogen-specific limits.

Crucially, the antimicrobial activity survived the removal of the living cells. Cell-free supernatants, the liquid fraction left after the bacteria are spun away, still inhibited pathogen growth by 84 to 89 percent in broth microdilution assays against E. coli, Salmonella, and S. aureus, particularly when derived from L. plantarum and L. casei. This matters because it demonstrates that the inhibitory power resides in secreted metabolites, a class of compounds often called postbiotics, rather than in any competitive behavior of the living microbes. For food manufacturers, that opens the door to using purified or concentrated extracts as shelf-life extenders without introducing live cultures into products where they might alter taste or texture.

The researchers then dissected what exactly was doing the killing. Lactic acid bacteria deploy a layered chemical arsenal: organic acids such as lactic and acetic acid, hydrogen peroxide, and proteinaceous toxins known as bacteriocins and bacteriocin-like inhibitory substances, or BLIS. By neutralizing the supernatants to remove the effects of acids and peroxide, then lyophilizing them into a stable powder, the team isolated the contribution of the BLIS fraction. Four of the five strains retained measurable activity after this treatment, with inhibition zones between 10 and 15.8 millimeters, confirming genuine BLIS production. Notably, Bifidobacterium animalis subsp. lactis lost its activity entirely once acids were neutralized, suggesting its antimicrobial punch comes primarily from pH effects rather than stable protein toxins.

Enzyme digestion experiments sealed the case for the proteinaceous nature of the compounds. Treating the lyophilized supernatants with trypsin, pepsin, and papain significantly reduced antimicrobial activity, with reductions ranging from about 1.3 to 11 percent. Pepsin inflicted the heaviest damage, hinting that the active peptides contain cleavage sites vulnerable to that particular enzyme. This enzyme sensitivity is a hallmark of bacteriocin-like substances and distinguishes them from non-protein antimicrobials. It also carries a safety implication: proteinaceous compounds are typically digested in the human gut, reducing the risk that they would disrupt beneficial microbiota or drive resistance the way broad-spectrum synthetic antibiotics can.

Quantification revealed just how potent these substances can be. Using arbitrary units and minimum inhibitory concentrations, the team found activity ranging from 133 to 1280 AU/mL across the target pathogens. L. rhamnosus GG delivered the single strongest result, achieving 1280 AU/mL against Salmonella Typhimurium with a remarkably low MIC of 1.54 mg/mL. Salmonella proved broadly susceptible across all five strains, an encouraging sign given the persistent burden of salmonellosis worldwide. Against E. coli, S. aureus, and P. aeruginosa, MIC values were higher, between 6.26 and 12.5 mg/mL for most strains, indicating moderate but still meaningful activity. The study also established a direct correlation between arbitrary units and MIC values, a methodological bridge that is rarely quantified and should make future comparisons between laboratories far more rigorous.

Beyond their chemical weapons, the strains passed several key probiotic fitness tests. All five displayed strong cell surface hydrophobicity above 50 percent, with three strains reaching approximately 65 percent, a trait associated with the ability to adhere to intestinal surfaces. Autoaggregation climbed steadily over time, with L. rhamnosus GG, L. casei, and B. animalis subsp. lactis all exceeding 85 percent after 24 hours. The bacteria also coaggregated with pathogens, clumping with S. aureus and E. coli at rates up to roughly 38 percent, a mechanism that can physically block pathogens from colonizing surfaces. Statistical analysis confirmed significant positive correlations between hydrophobicity, autoaggregation, and coaggregation, suggesting these adhesion traits work in concert. On the safety side, most strains were sensitive to clinically important antibiotics such as azithromycin, tetracycline, and penicillin, though all showed intrinsic resistance to aminoglycosides and norfloxacin, a pattern considered typical and non-transferable in lactic acid bacteria. One caveat stands out: L. plantarum NBRC 3070 was resistant to every antibiotic tested, a finding the authors flag as warranting deeper genetic investigation before any food application.

Perhaps the most practically valuable insight concerns timing and temperature. The team tracked antimicrobial production over 48 hours of anaerobic growth at both 30 and 37 degrees Celsius. Activity appeared as early as four hours into growth, but peak production, exceeding 90 percent inhibition of the indicator organism, arrived during the stationary phase: at 36 hours when cultures were held at 30 degrees, and at 24 hours at 37 degrees. Warmer temperatures accelerated growth and acidification but did not proportionally boost antimicrobial yield, and temperature alone had no significant effect on production levels. Instead, the interplay of time, temperature, and strain identity governed the output, with falling pH and accumulating biomass acting as triggers for biosynthesis. For industrial fermenters, this defines a precise harvest window, after which activity gradually declines, likely due to proteolytic degradation of the active compounds.

The implications extend well beyond the laboratory bench. With the World Health Organization identifying antimicrobial resistance as one of the top global public health threats, and with chemical preservatives facing growing consumer skepticism, bacteriocin-based biopreservation occupies a rare sweet spot: effective, natural, and generally regarded as safe. Nisin, a bacteriocin from a related lactic acid bacterium, has already been licensed as a food additive for decades, proving the commercial pathway exists. What this study adds is a rigorous, comparative evaluation of five industry-relevant strains, complete with optimized production conditions, quantified potency, and enzyme-confirmed mechanisms. The authors are candid about the limitations: the work was conducted entirely in vitro, the molecular structures of the BLIS remain uncharacterized, and the resistance profile of L. plantarum needs clarification. Still, the convergence of strong antimicrobial activity, favorable surface properties, and acceptable antibiotic susceptibility profiles positions these five strains, and especially L. plantarum and L. rhamnosus GG, as leading candidates for the next generation of natural food preservatives. In the escalating contest between superbugs and the food supply, the humble yogurt bacterium may prove to be an unlikely but formidable ally.

Subject of Research: Probiotic lactic acid bacteria and their antimicrobial substances against foodborne pathogens

Article Title: Evaluation of Probiotic Properties and Antimicrobial Substances Produced by Five Lactic Acid Bacteria Against Foodborne and Spoilage Pathogens

Article References: Rahman, M. M., Sazili, A. Q., Ahmad, S. A., Khalil, K. A., Ismail‐Fitry, M. R., & Sarker, M. S. K. (2026). Evaluation of Probiotic Properties and Antimicrobial Substances Produced by Five Lactic Acid Bacteria Against Foodborne and Spoilage Pathogens. MicrobiologyOpen, 15(5), Article e70052. https://doi.org/10.1002/mbo3.70052

Image Credits: AI Generated

DOI: 10.1002/mbo3.70052

Keywords: lactic acid bacteria, probiotics, bacteriocin-like inhibitory substances, foodborne pathogens, antimicrobial resistance, biopreservation, Lactiplantibacillus plantarum, Lacticaseibacillus rhamnosus GG, postbiotics, food safety, minimum inhibitory concentration, cell surface hydrophobicity