Abstract
Faecal samples of two Mexican breast-fed infants were used to isolate a Bifidobacterium strain in a selective medium. This strain was characterised biochemically for carbohydrate fermentation patterns and the fructose-6-phosphate phosphoketolase assay; genetically it was identified by PCR using genus-specific primers. The isolated strain was named Bifidobacterium JCLA3 and was grown on four different carbon sources; the respective growth kinetics of glucose, lactose, inulin and sucrose were measured. The highest cellular yield was presented in the culture media containing sucrose, followed by inulin, while on glucose and lactose, the cellular yield was lowest; these results correlate with the characteristic that bifidobacteria prefer complex carbon sources. We also determined the expression of the ack and ldh genes. The ldh gene presented high levels of expression regarding the ack gene; nevertheless on sucrose, the expression was lower regarding the other three substrates. The highest expression level of the ack gene was from the culture media with glucose, followed by inulin, sucrose and lactose. Key words: Bifidobacterium, characterisation, gene expression.
Highlights
Bifidobacteria represent a significant proportion of the infant and adult gut microbiota
The highest cellular yield was presented in the culture media containing sucrose, followed by inulin, while on glucose and lactose, the cellular yield was lowest; these results correlate with the characteristic that bifidobacteria prefer complex carbon sources
Colonies have been identified as members of the genus Bifidobacterium by the detection of fructose-6-phosphate phosphoketolase (F6PPK) (Grill et al, 1995)
Summary
Bifidobacteria represent a significant proportion of the infant and adult gut microbiota. The isolation of bacteria from gut microbiota is important to characterise and analyse differences among strains. Selective and differential media have been described for the isolation of Bifidobacterium spp., their identification is not clear because it is based on phenotypic characteristics that do not always provide reliable results. It is known that bifidobacteria can change their morphology depending on the culture medium, growth and culture conditions (Bonaparte et al, 2001; Klein et al, 1998). Colonies have been identified as members of the genus Bifidobacterium by the detection of fructose-6-phosphate phosphoketolase (F6PPK) (Grill et al, 1995). The test is time consuming and laborious (Scardovi, 1986; Biavati et al, 1992; Tannock, 1999)
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