Microbial colonization of the infant gut is essential for the development of the intestine and the immune
system. The intestinal microbiota of full-term breast-fed infants is considered as the health standard for
newborns. A culture medium containing formula milk was designed, which allowed a balanced growth
of intestinal microorganisms and was used to perform fecal batch cultures from preterm babies. Sixteen
Bifidobacterium strains and fructooligosaccharides (FOS) were tested for their ability to modulate in vitro
the intestinal microbiota. The production of short chain fatty acids (SCFA) was measured by Gas Chromatography
and the levels of some anaerobe (Bifidobacterium and Bacteroides groups) and facultative
anaerobes (Enterobacteriaceae, Enterococcaceae, Weissella group, and Klebsiella pneumoniae) were
determined by quantitative PCR. Results were referred to a fecal negative control culture without
microorganisms or FOS added. Strains that in fecal cultures counteracted better the aberrancies previously
found in feces of preterm babies, as compared with full-term breast-fed infants, were selected. The
three Bifidobacterium bifidum strains tested in this work promoted the most suitable shifts in SCFA and in
the ratio of variables facultative anaerobes to anaerobes. Two Bifidobacterium breve strains complied with
the requirement for facultative anaerobes and anaerobes and one of them also promoted a suitable shift
of SCFA. Bifidobacteria behaved similarly as FOS regarding the microbial profiles in fecal cultures but the
production of lactic and acetic acid was much lower. B. breve and B. bifidum strains selected represent
promising candidates for their assessment in more complex in vitro and in vivo models.
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