The third CDS (methyl transferase, SCAZ3_05815) was homologous with the same DNA methylase of E. coli, as for both the plasmid and phage, and therefore may provide the ICE with similar protection from host restriction nucleases. A BLASTn search detected the ICE in two additional Streptococcus species: S. agalactiae (strains S3-026 and NEM316) and S. dysgalactiae subsp. dysgalactiae. Global nucleotide alignment showed these H 89 molecular weight ICE to have
only moderate identity with the S. canis ICE: 58.2%, 55.0%, and 60.1% respectively. In addition to the genes described, the S. canis ICE also contained the lactose operon Lac.2 [52, 64], suggesting that the ability to ferment lactose may have been acquired via lateral gene transfer. Furthermore, Lac.2 is also contained within the S. agalactiae (NEM316) and S. dysgalactiae subsp. dysgalactiae ICE, suggesting that these strains may have check details also acquired the ability to ferment lactose via lateral gene transfer.
Given S. canis strain FSL S3-227’s association with the bovine environment, it is notable that there is a putative nisin resistance CDS (SCAZ3_06155) within the genome. Nisin is a lantibiotic produced by some strains of the mastitis causing pathogen Streptococcus uberis, and has been shown to provide these strains with a competitive advantage during intramammary infection when compared to non-producer strains . The gene operon required for nisin production is also present in bovine isolates of S. agalactiae. Although S. canis strain FSL S3-227 lacked this operon, the presence of a nisin resistance CDS might assist S. canis during intramammary infection. Population genetics To assess the population genetic structure of S. canis we ribotyped
an additional 82 isolates obtained from bovine, canine, and feline hosts (see Methods). Of these, a subset of 46 isolates was selected for multi locus sequence typing (see Methods). The ribotyping revealed a total of 17 ribotypes for all 83 isolates CYTH4 (Table 1). With one exception, isolates from multiple cows within each dairy herd belonged to a single ribotype per herd. This supports previous observations, which found that mastitis outbreaks due to S. canis were generally caused by a single strain within a herd [10, 12], suggesting contagious transmission, exposure to a point-source, or host-adaptation of specific S. canis strains . Among the 46 isolates selected for the MLST scheme, we identified 16 sequence types (STs) (see Additional file 5 for allelic profiles). Diversity among canine isolates was substantially higher than among bovine isolates (Table 2). For example, there were 14 canine STs (diversity: 0.90) compared to 3 bovine STs (diversity: 0.49). For the ribotypes, there were 13 canine ribotypes (diversity: 0.88) compared to 4 bovine ribotypes (diversity: 0.67). Nucleotide diversity showed a different pattern.