Bifidobacteria are prevalent
in the faeces of breast-fed infants. Species that are frequently isolated are Bifidobacterium breve, B. infantis, B. longum, Bifidobacterium bifidum, Bifidobacterium catenulatum and Bifidobacterium dentium (Sakata et al., 2005; Shadid et al., 2007). However, only B. infantis, which possesses a specialized HMO utilization cluster composed of β-galactosidase, fucosidase, sialidase and β-hexosaminidase is capable of releasing and utilizing monosaccharides from complex HMOs (Ward et al., 2006, 2007; Sela et al., 2008). In contrast, B. bifidum releases monosaccharides from HMOs but is not able to use fucose, sialic acid and N-acetylglucosamine; B. breve was able to ferment but not release monosaccharides (Ward et al., 2007). Lactobacillus species frequently isolated from neonate faeces are L. fermentum, Lactobacillus casei, Lactobacillus paracasei, L. delbrueckii, L. gasseri, L. rhamnosus and L. plantarum (Ahrnéet al., 2005; Haarman & Knol, 2006). In vitro digestion selleckchem of HMOs by LAB has previously been examined for L. gasseri, L. acidophilus, S. thermophilus and L. lactis and digestion of HMOs was low in comparison with B. infantis (Ward et al., 2006; Sela et al., 2008; Marcobal et al., 2010). Accordingly, in this study, defined HMOs acted as poor substrate for the LAB tested. Only L. acidophilus and L. Cobimetinib ic50 plantarum whole cells, which showed
the widest hydrolysing activity on oNPG and pNP analogues, were capable of releasing mono- and disaccharides from defined HMOs. Hydrolysis activity was limited to tri- or tetrasaccharides; lacto-N-fucopentaose I was not metabolized, probably because higher oligosaccharides are not transported to the cytoplasm. Dedicated transport systems for oligosaccharides are generally absent in lactobacilli. To date, only two transport systems specific
for fructooligosaccharides and maltodextrins have been identified in L. plantarum and L. acidophilus (Barrangou et al., 2003; Saulnier et al., 2007; Nakai et al., 2009). HMO hydrolysis by LAB was absent or low but extracellular hydrolysis of HMOs by other microorganisms in the intestine may liberate monosaccharides for subsequent use by LAB. It was thus investigated whether LAB could use HMO components as substrate. All LAB strains tested grew to highest OD in the presence of lactose and glucose. N-acetylglucosamine Selleck Decitabine was fermented to various extents and all LAB strains formed lactate and acetate is a molar ratio of 2 : 1 from N-acetylglucosamine, in agreement with previous reports for Lactovum miscens (Matthies et al., 2004). This indicates that the glucosamine moiety was metabolized to 2 mol lactate after liberation and release of the acetyl moiety. Interestingly, both hetero- and homofermentative LAB metabolized the glucose moiety of N-acetylglucosamine via the Embden–Meyerhof pathway, whereas glucose was metabolized via the phosphoketolase pathway by all obligate heterofermentative LAB (L. reuteri, L. fermentum and L. mesenteroides subsp. cremoris).