Capsular typing of Streptococcus agalactiae (Lancefield group B streptococci) from fish using multiplex PCR and serotyping

Authors: Shoemaker, Craig; Xu, Dehai; Garcia, Julio; Lafrentz, Benjamin

Submitted to: European Association of Fish Pathologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2017
Publication Date: 9/8/2017
Citation: Shoemaker, C.A., Xu, D., Garcia, J.C., LaFrentz, B.R. 2017. Capsular typing of Streptococcus agalactiae (Lancefield group B streptococci) from fish using multiplex PCR and serotyping. Bulletin of the European Association of Fish Pathologists. 37(5):190-197.

Interpretive Summary: Streptococcus spp., including Streptococcus agalactiae (Lancefield group B streptococci) are considered emerging Gram positive bacterial pathogens responsible for approximately $1 billion USD in annual losses to the $7 billion global tilapia (Oreochromis sp.) aquaculture industry. There is an urgent need to identify different capsular types of S. agalactiae from farmed and wild fish in order to combat Streptococcus disease. This study evaluated a published multiplex polymerase chain reaction (PCR) capsular typing assay and commercially available antiserum to assign capsular type to a total of 40 S. agalactiae isolates including American Type Culture Collection (ATCC) isolates as controls. The capsule is a sugar containing material on the surface of these bacteria that is important for virulence and antigenicity including serotype. The evaluated multiplex PCR was modified from the original description to include primers specific for capsular types Ia, Ib, II and III. These are the common capsular types reported from fish and aquatic animals. The modified PCR assay that includes a 688 base pairs (bp) ampicon based on the capsular polysaccharide L (cpsL) gene diagnostic for S. agalactiae effectively typed S. agalactiae isolates from fish. Most isolates from North, Central and South America were assigned to capsular type Ib based on the presence of three amplicons of 688, 621 and 272 bp. A commercial serotyping system mostly confirmed the molecular methodology. The modified multiplex PCR assay can be used to determine the capsular type of S. agalactiae present on a farm and/or in a region, and an understanding of this will assist research and disease management strategies (i.e., vaccination and selective breeding).

Technical Abstract: Streptococcus spp. including Streptococcus agalactiae (Lancefield group B streptococci) are considered emerging pathogens responsible for approximately $1 billion USD in annual losses to the global tilapia (Oreochromis sp.) aquaculture industry. This study evaluated a published multiplex PCR capsular typing assay and commercially available antiserum to assign capsular type to a total of 40 S. agalactiae isolates including American Type Culture Collection (ATCC) isolates as controls. The multiplex PCR was modified from the original description to include primers specific for capsular types Ia, Ib, II and III, that are the capsular types reported from aquatic animals. Phenotypic variation was noted among the S. agalactiae isolates in this study based on API® 20 Strep strip results. The modified PCR assay that includes a 688 bp ampicon based on the cpsL gene diagnostic for S. agalactiae effectively typed piscine S. agalactiae isolates. Most isolates (28 of 30) from North, Central and South America were assigned to capsular type Ib based on the presence of three amplicons of 688, 621 and 272 bp. A commercial serotyping system mostly confirmed the molecular methodology. The modified multiplex PCR assay can be used to determine the capsular type of S. agalactiae present on a farm and/or in a region, and an understanding of this will assist research and disease management strategies (i.e., vaccination and selective breeding).