Endogenous Ethanol-producing Bacteria Interference in Pathogen-host Crosstalk

Abstract

Background and Aims: The host micronutrient milieu is a compilation of factors of both endogenous and exogenous origin. This milieu shapes the host's immune responses and can control the inflammatory response of the host when infected. Among vitamins, B12 plays a key role in the defense process because there is intense competition for it between pathogenic invaders and infected host cells. Alcoholic beverages and antibiotics can cause biological (in vivo) interferences that affect pathogen-host crosstalk. Ethanol is known to interfere with the absorption, distribution, and excretion of vitamin B12 in men and animals. However, the molecular mechanisms underlying this backdrop are not fully understood. Here we explored how Gram-positive ethanol-producing and Gram-negative vitamin B12-producing microbes of the infected milieu interact to influence biomarkers of host cell defense re-sponses in absorbing, digesting, and defensive cells. Material and Methods: We investigated two different cell types of colon and liver origin, hepatic-like Huh7 cells and HT- 29/B6 colon cells. To assess the ability of secreted factors from bacteria to exert influence on co-cultured cell's secretion of host-defense markers in response to invading pathogens, co-cultured human colonic HT-29/B6 and human hepatic Huh-7 (hereafter Huh7) cells were stimulated or not with Klebsiella pneumoniae 52145 for 24 h in the presence or absence of either Weissella confusa strain NRRL-B-14171 (as a Gram-positive producer of ethanol), Limosilactobacillus reuteri 20016 (as a Gram-positive producer of vitamin B12), or Pseudomonas nitroreducens 1650 (as a Gram-negative producer of vitamin B12). After stimulation, molecular functional biomarkers of host cell defense re-sponses including total MMP-1, lysozyme activity, ALP, and IL-25 were measured. Results: While simultaneously reducing IL-25 secretion, Kp52145 alone significantly elicited MMP-1, lysozyme, and ALP secretion from co-cultured cells, as compared to no treatment. When compared with Kp 52145 stimulation alone, Pn1650 significantly potentiated MMP-1 and lysozyme secretions from Kp 52145-stimulated co-cultured cells by 29.7% and 67.4%, respectively. Simultaneously, a po-tentiated suppression (an overall decrease of 77.3%) in IL-25 secretion occurred 24 hours after Kn52145 plus Pn1650 administration. Compared to Kp52145-stimulation alone, treatment with W. con-fusa NRRL-B-14171 and Kp52145-stimulated co-cultured cells was associated with significant additive induction of MMP-1 and lysozyme secretions. However, compared to Kp52145-stimulation alone, W. confusa NRRL-B-14171 treatment significantly potentiated Kp52145-induced suppression of IL-25. Using the same condition as mentioned above and compared to Kp52145-stimulation alone, L. reuteri 20016 treatment altered the secretion pattern in response to Kp52145: L. reuteri 20016-treated cells displayed less aversive responses towards Kp52145, suggesting that L. reuteri 20016 modulation may act differently on Kp52145 - induced signaling. Conclusion: Gram-negative and Gram-positive vitamin B12- producing bacteria differently affect the secretion of key immune biomarkers in co-cultured HT-29/B6 and Huh7 cells following exposure to Kp52145. Ethanol-producing bacteria additively potentiate pathogenicity and inflammatory responses upon infection. To confirm the biological consequences of these effects on human gut microbiota and health, further studies are warranted, incorporating ex vivo studies of human colon samples and host biomarkers such as cytohistological, molecular, or biochemical measurements.