Identification and characterization of Streptococcus agalactiae isolated from horses.

The study highlights the identification and distinguishing features of two distinct forms of Streptococcus agalactiae, a type of bacteria, found among horses. The bacteria instances were verified using different genetic testing techniques and matched human isolations of the same species.

Methods Used for Identification

• The identification of the cultures as Streptococcus agalactiae was first established on the basis of positive reactions with group B-specific antiserum, biochemical characteristics, CAMP tests, and pigmentation.
• Further validation was achieved through PCR amplification of the 16S rRNA gene followed by RsaI restriction, which was indicative of S. agalactiae.
• More definitive identification was done through amplification of species-specific parts of other genes such as the 16S-23S rRNA intergenic spacer region, and the CAMP-factor (cfb) gene.

Serotype Classification

• Through these tests, six isolates were categorized as serotype III/Rib, while one was classified as serotype Ia/cbeta.
• The presence of certain protein antigens (Rib and cbeta) was validated through PCR amplification of specific genes.

Distinguishing Features

• The six isolates identified as serotype III/Rib were negative for the enzyme hyaluronidase, had a hylB gene of a particular size (4.6 kb), and an insertion element of a different size (IS1548 of 0.98 kb).
• On the other hand, the isolate identified as serotype Ia/cbeta, exhibited hyaluronidase activity, had a hylB gene of a different size (3.3 kb), and lacked the IS1548 insertion element.
• All seven isolates however, possessed the insertion element ISSag2 and genes encoding specific proteins – laminin binding surface protein Lmb, and C5a peptidase (scpB gene).

Comparison with Human Isolates

• The characteristics of the group B streptococci isolates, identified from horses in this study, were found to be similar to those isolated from human samples.