L. lactis I-1631, a strain often used by the food industry for yogurts and cheeses, was found to produce the antioxidant enzyme superoxide dismutase A (SOD A) when exposed to the ‘harsh’ environment of an inflamed gut. But not only that, the bacterial strain also ruptured (lyse) to release the SOD A to reduce oxidative stress.
“Our experiments support that the non-engineered L. lactis I-1631 strain reduces colitis in three murine models, does so in a SOD A-dependent fashion, and requires host lysozyme to facilitate delivery,” wrote the researchers from Harvard’s Chan School of Public Health and Danone Nutricia Research and the Institut National de la Recherche Agronomique (UMR 1319 Micalis) in France.
The L. lactis would not be strictly classed as a probiotic because it is not a live organism when it confers its health benefit [Probiotics are defined as “live microorganisms that when administered in adequate amounts confer a health benefit on the host”.]
“Our study challenges the perception that beneficial microbes need to remain viable throughout the gastrointestinal tract to confer their health benefit,” wrote the researchers in the Proceedings of the National Academy of Sciences of the USA.
“Our findings also delineate a mechanism by which beneficial microbial strains offer up benefits to the host and highlight how specific characteristics of the host may be necessary to promote a bacterium’s beneficial activity,”they added.
The researchers used three different types of mouse models of IBD: one mouse model is lacking two genes that causes them to spontaneously develop a bad ulcerative colitis-like disease; the second one is a mouse that lacks the ability to make the anti-inflammatory cytokine IL-10; and the last model is a mouse that sensitive to dextran sulfate sodium and consuming the sugar disrupts the lining cells of the large intestine and produces very bad intestinal inflammation.
The fermented milk product had an effect in all three of the inflammation models, said the researchers.
Because the inflamed gut is a harsh environment, the L. lactis bacteria produced SOD A to help protect it from the reactive oxygen species present in the intestines. The benefit to the host was obtained when the bacteria ‘exploded’ in the right place, releasing the SOD into the intestine.
“We found that an L. lactis strain, which was not appreciated as a beneficial microbe and that naturally produces superoxide dismutase, attenuates colitis in three different mouse models and lowers colonic epithelial oxidative stress,” wrote the researchers.
“Neither colonization nor an intact bacterium throughout the colon per se is required. Rather, lysozyme-mediated lysis at inflamed colonic sites contributes to L. lactis’ release of its cytoplasmic SOD A, which is necessary for L. lactis’ colitis-attenuating activity.”
“Collectively, our results suggest that a bacterium used in FMPs may have an activity that ameliorates intestinal inflammation and that targeted delivery of this beneficial activity need not be synthetically engineered,” they concluded.
The study was partly funded by Danone Nutricia Research, the National Cancer Institute, and the National Institute of Allergy and Infectious Diseases.
Source: Proceedings of the National Academy of Sciences of the USA
Published online ahead of print, doi: 10.1073/pnas.1501897112
“Host lysozyme-mediated lysis of Lactococcus lactis facilitates delivery of colitis-attenuating superoxide dismutase to inflamed colons”
Authors: S.A. Ballal, P. Veiga, K. Fenn et al.