The Screening of Hydrogen Peroxide-Producing Lactic Acid Bacteria and Their Application to Inactivating Psychrotrophic Food-Borne Pathogens

Abstract

Lactic acid bacteria were isolated from various food samples and evaluated for hydrogen peroxide (H2O2) production. Cells suspended in 0.5% (wt/vol) glucose plus 0.5% (wt/vol) lactate (pH 7.0) were incubated for 5 h at 37 degrees C under aeration. Among 193 strains, 27 strains accumulated 201-300 ppm H2O2, and 4 strains accumulated more than 301 ppm H2O2 in the cell suspensions. Among the 9 high-level H2O2-producing strains, 8 strains were identified as Lactococcus lactis subsp. lactis. The cell-free filtrate from Lc. lactis subsp. lactis AI 62, which contained approximately 350 ppm H2O2, was evaluated for antimicrobial activity against Enterococcus faecalis, Ent. faecium, enterotoxigenic Escherichia coli, Listeria ivanovii, Staphylococcus aureus, Yersinia enterocolitica, and Aeromonas hydrophila. After 1 h incubation at 30 degrees C in the cell-free filtrate, the initial viable cell counts of the target bacteria (5.53-6.00 log cfu/mL) were reduced by 0.12-5.00 log units, except in the case of enterococci. The sensitivity varied with the bacterial species and pH. The enterococci were resistant to the treatment. Our results show that H2O2 accumulated by lactic acid bacteria in a cell suspension is very effective in reducing the viable cell count of food-borne pathogens.

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“…The antiinflammatory effects of lactobacilli are multifaceted, but lactobacilli-mediated killing of pathogens (e.g. S. enterica , E. coli ) has been firmly associated with their H 2 O 2 production [73] . Even some catalase-negative pathogens use endogenous H 2 O 2 production for intra- and inter-bacterial signaling.…”

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“…The scarce studies on H 2 O 2 production by LAB in a food context report the ability of LAB isolated from food products, including dairy products, to produce H 2 O 2 . However, H 2 O 2 production assays are generally performed in laboratory conditions (Ito et al 2003;Enitan et al 2011) rather than in situ in dairy products, probably because of the difficulty to quantify this unstable metabolite.…”

“…The ability of LAB to produce H 2 O 2 appears to be strain-dependent. Ito et al (2003) evaluated the ability of 193 LAB strains isolated from various food products to produce H 2 O 2 and found strong variations between strains. The scarce studies on H 2 O 2 production by LAB in a food context report the ability of LAB isolated from food products, including dairy products, to produce H 2 O 2 .…”

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“…Comm.). The anti-microbial effect of � 2 O 2 has been attributed to its strong oxidizing effect on bacterial cells and to the destruction of the molecular structure of cell proteins (Ito et al, 2003;Zalán et al, 2005). �owever, there is no information available on the effect of � 2 O 2 on rumen fermentation.…”