Genetic organization of Streptococcus salivarius 24SMBc blp -like bacteriocin locus.

In this paper, we describe, for the first time, the genetic organization of the blpU -like cassette in Streptococcus salivarius 24SMBc by entire genome sequencing. This strain has recently been found useful and widely applied as an oral probiotic in the prevention of recurrent otitis media. The 24SMBc blpU -like cassette  is 8,023 bp in length, organized in 11 orfs, of which orf 8 encodes for the pore-forming peptide bacteriocin, belonging to class IIc, with a double-glycine leader peptide. The first characterization of blp locus was described in Streptococcus pneumoniae, showing a crucial role in interspecies competition within the nasopharynx. The salivarius blpU -like cassette is inserted upstream of the pep X gene in the chromosome. A hypervariable region between pepX and o rf1 was found and used as a specific target able to distinguish S. salivarius 24SMBc from all other streptococci. All orfs carried by the blp -like cassette are functionally expressed (qPCR assays). Our results contribute to elucidate the microbial interactions in the nasopharynx, underlining the potential role of  the blp locus in human nasopharyngeal colonization.