A new selective antibiotic-free medium forBifidobacterium spp. is defined. This medium has lactulose as the main carbon source and includes methylene blue, propionic acid, and lithium chloride as inhibitors of some related bacterial species. The low pH of the medium contributes to the inhibition of the growth ofEnterobacteriaceae. This new selective medium has a simple composition, and the level of recovery it yields is similar to those yielded by nonselective media for Bifidobacterium strains. It could thus be used for routine analysis in environmental or food microbiology.

A new, simple, and specific protocol to discriminate between human and animal fecal pollution is described. The procedure is based on the detection of certain Bifidobacterium species in the samples. Two 16S rRNA gene-targeted probes are described. One of these probes (BDE) has as its target a region of the 16S rRNA gene of Bifidobacterium dentium, a Bifidobacterium species of exclusively human origin. The other probe (BAN) is based on the sequence of a region of 16S rRNA gene for several Bifidobacterium species related with animal origins. The specificity of both probes was evaluated by using 24 Bifidobacterium species, and their threshold detection limit was established by DNA-DNA hybridization. DNA-DNA hybridization with the BDE probe showed it to be specific for B. dentium, whereas that with the BAN probe showed it to be specific for B. animalis, B. asteroides, B. coryneforme, B. cuniculi, B. globosum, B. magnum, B. minimum, and B. subtile. A simple and specific protocol was also developed for the detection of their target species in environmental samples (sewage and feces). DNA-DNA hybridization with the BAN probe was only positive for samples from cattle and goats. Thus, this probe is not suitable for the identification of any animal fecal pollution. Whereas all samples with human fecal pollution showed a positive DNA-DNA hybridization result with the BDE probe, none of those with animal fecal pollution did. Therefore, this finding supports the potential use of this probe in detecting fecal pollution of human origin.

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