Different studies suggested that colonic gas production favours infantile colic, however the speculation is not supported by well-built scientific researches. Recently, it has been evidenced that gas forming coliform concentration is higher in colicky infants than in healthy controls [16
]. Various medical interventions have already been applied to improve symptoms related to infantile colic. Simethicone, a defoaming agent, has been promoted as an effective treatment reducing the formation of intraluminal gas, even though existing data do not demonstrate conclusive benefit of such therapy [24
]. Alternative solutions to the problem are therefore looked forward.
Recently the benefit of supplementation with Lactobacillus reuteri
(American Type Culture Collection Strain 55730 and DSM 17 938) has been reported opening a new therapeutic approach [14
], even though clinical trials are needed to promote new treatments to reduce abdominal pain related to infantile colic [16
Coliform growth and carbohydrate fermentation affect ammonia absorption and urea nitrogen recycling and excretion. We observed reduction in fecal ammonia concentrations in breastfed infants given L. reuteri
and this could be related to modification of bacterial enzyme activity depending on gut microbiota and suggested that gas forming coliforms may be involved in determining colonic fermentation and consequently excessive intraintestinal air load, aerophagia and pain, characteristic symptoms of colic crying, but many aspects of these relationships are still unclear [15
]. In the present study we confirmed the higher count of coliforms in colicky infants with respect to non colicky newborns, as already observed in a previous work [17
Previous studies had shown that some Lactobacillus
spp. strains possessed inhibitory activity against E. coli
, preventing the binding of enteropathogenic E. coli
and other pathogens to intestinal cells [26
]. More recently it has been shown that a synbiotic diet containing both prebiotics and probiotics reduces population of intestinal E. coli
and the pathogen population in rats [27
Given these findings, in this work new Lactobacillus strains possessing anti-microbial activity against gas-producing coliforms were searched and the interaction between selected lactobacilli and coliforms was studied.
Coliforms were isolated from stools of colicky infants and characterized taxonomically and for gas production. They were all gas-producing strains and were attributed to 6 different species. The taxonomic identification of the isolated strains and their relative percentage within the coliform group confirmed the results obtained in a previous study, being E. coli
the most represented species [17
]. Two of the 27 lactic acid bacteria assayed in this study, L. delbrueckii
DSM 20074 and L. plantarum
MB 456, were able to inhibit the growth of gas-forming coliforms belonging to the different species isolated from colicky infants. The extent of the inhibitory activity was similar for all the coliforms assayed (Table ), although it was higher for the DSM 20074 strain with respect to the other one. Moreover, the capability of the DSM 20074 strain of hindering the growth of coliforms was also observed in a liquid co-culturing assay. Therefore, this strain appears to be a good candidate to relieve symptoms caused by gas-producing coliforms in colicky infants.
The antagonistic activity of the two Lactobacillus
strains was only evidenced when harvested cells were applied, whereas the neutralized culture supernatants did not exert any activity on the same coliforms (Figure ). The inhibitory activity of lactic acid bacteria has generally been ascribed to two mechanisms, which can often coexist: i) the production of bacteriocins or bacteriocin-like molecules, which are very often secreted outside the cell [28
] and ii) the production of inhibitory non proteinaceous metabolites such as organic acids, carbon dioxide, ethanol, hydrogen peroxide and diacetyl, whose anti-microbial action is well known [30
]. In addition, Alakomi et al. reported that lactic acid can permeabilize the membrane of Gram negative bacteria by a mechanism of outer membrane disruption [31
]. In the case of the two lactic acid bacteria showing inhibitory activity against coliforms in this work, this activity is linked to the presence of the whole cells, although it is not possible to exclude that putative inhibitory molecules are present in the supernatants at such a low concentration that their activity cannot be detected by the assay employed. Therefore, it is not possible to clearly ascribe the inhibitory activity to a defined group of molecules and further studies are necessary to characterize the exact mechanism of inhibition.