Detection of infant faecal bifidobacteria by enzymatic methods

Twenty-nine infants had high numbers of bifidobacteria (usually higher than 9 log CFU/g) in their faeces. Seventeen infants (35%) did not contain detectable amounts of bifidobacteria in their faecal samples. The remaining five individuals had low counts of bifidobacteria (3-6 log CFU/g). Most negative infants possessed major amounts of clostridia in their faecal flora. There were no significant differences among bifidobacterial counts obtained by cultivation and FISH, detection of F6PPK, α-galactosidase and α-glucosidase activities could routinely be used for the rapid and simple detection of bifidobacteria in infant faecal samples. Bifidobacterial colonies were identified using enzymatic tests and PCR procedure based on 16S rRNA gene sequences species-specific primers. In 14 samples, the identifications of individual isolates were compared with direct analyses of faeces using the nested PCR-denaturing gradient gel electrophoresis (nested DGGE) procedure. The results obtained in several cases are not identical. Bifidobacterium longum and Bifidobacterium breve were most frequently identified. Bifidobacteria-positive samples had high activities of α-galactosidase and α-glucosidase. On the contrary, negative samples missed either one or both of these enzymatic activities. While all positive samples tested showed distinctive fructose-6-phosphate phosphoketolase activity (F6PPK), none of the negative samples expressed F6PPK activity.