Antagonistic effect of Lactobacillus strains against gas-producing coliforms isolated from colicky infants

Strains of coliforms were isolated from stools of 45 colicky and 42 control breastfed infants in McConkey Agar and identified using PCR with species-specific primers, and the BBL？ Enterotube？ II system for Enterobacteriaceae. Gas-forming capability of coliforms was assessed in liquid cultures containing lactose as sole carbon source. The average count of total coliforms in colicky infants was significantly higher than controls: 5.98 (2.00-8.76) log10 vs 3.90 (2.50-7.10) CFU/g of faeces (p = 0.015). The following strains were identified: Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter aerogenes, Enterobacter cloacae and Enterococcus faecalis. Then, 27 Lactobacillus strains were tested for their antagonistic effect against coliforms both by halo-forming method and in liquid co-cultures. Lactobacillus delbrueckii subsp.delbrueckii DSM 20074 and L. plantarum MB 456 were able to inhibit all coliforms strains (halo-forming method), also in liquid co-cultures, thus demonstrating an antagonistic activity.This study shows that two out of 27 strains of Lactobacillus examined possess an antimicrobial effect against six species of gas-forming coliforms isolated from colicky infants. Our findings may stimulate new researches to identify which Lactobacillus strains can improve colicky symptoms by acting on coliforms gut colonization.The intestinal microbiota exerts many physiological functions such as metabolic and trophic activities and plays an important role in the "barrier effect" against exogenous microbes [1]. It is also involved in the development and activation of the intestinal immune system: a recent study suggests that a more diverse gut microbiota early in life might prevent allergy development [2]. Gut microbiota is acquired during early life and intestinal colonization starts immediately after birth. The ability of species to establish themselves durably in the colonic ecosystem depends on complex interactions between host and bacteria as w