Abstract
Background: Bifidobacterium are recognized as probiotic microorganisms since they provide several health benefits to human hosts including improvement of lactose utilization, increased immunity in animal hosts and antagonistic effect towards pathogenic bacteria. Safety and survival during passage through the human gut as well as their ability to resist technological handling are among the requirements asked to a probiotic bacteria.
Objective: To evaluate the “in vitro” antimicrobial activity, tolerance to acidic conditions and to bile salts in Bifidobacterium spp isolated from healthy infants.
Methods: Fifteen bifidobacterial strains isolated from faecal samples from Chilean infants were evaluated. The antagonistic effect of bifidobacteria towards Escherichia coli O157:H7 ATCC 35150 and Salmonella enterica isolated from food (Al-75) was studied by the agar spot test in MRS agar and sodium bicarbonate buffered (2g/l) MRS medium. The tolerance to acidic conditions was determined using a microplate assay MRS broth at different pH (4.0, 4.2 and 4.5). The bile tolerance was done in the same way, but using MRS -3% bile salt broth.
Results: 9/15 (60%) bifidobacterial strains produced inhibition zones larger than 15 mm towards both enteropathogens. Only 3/15 (20%) strains showed no effect. When the same starins were tested on bicarbonate buffered MRS agar 3/9 strains previously tested showed antimicrobial activity, but only one them maintained the inhibition zones towards at least one of the pathogens. Even though none of the bifidobacteria was able to multiplicate in the acidic conditions tested 4/15 strains remained viable. Finally, 3/15 bifidobacterias tolerated bile at 0.3%.
Conclusions: 6 bifidobacterial strains are now available, that inhibit Salmonella enterica “in vitro”, although the mechanism is unknown it should be different to the production of organic acids, in addition one of the strains resists bile salts and acidic conditions.
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Rivas, P., Troncoso, M. & Figueroa, G. Probiotic Potencial of Bifidobacterium SPP Isolated from Healthy Infants: P100. Pediatr Res 60, 639 (2006). https://doi.org/10.1203/00006450-200611000-00046
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DOI: https://doi.org/10.1203/00006450-200611000-00046