ARS | Publication request: GENOMIC DIVERSITY OF STREPTOCCOCUS AGALACTIAE ISOLATES FROM MULTIPLE HOSTS AND THEIR INFECTIVITY IN NILE TILAPIA

Submitted to: International Symposium on Talipia in Aquaculture
Publication Type: Proceedings/Symposium
Publication Acceptance Date: August 1, 2008
Publication Date: October 12, 2008
Citation: Evans, J.J., Klesius, P.H., Bohnsack, J.F., Pasnik, D.J., Garcia, J.C., Whiting, A.A., Shoemaker, C.A. 2008. Genomic diversity of streptoccocus agalactiae isolates from multiple hosts and their infectivity in nile tilapia. Proceedings of the 8th International Symposium on Talipia in Aquaculture. Cairo, Egypt October 12-14-2008. Volume 2: p 1199-1209.

Interpretive Summary: Our laboratory has conducted multiple studies to investigate the genomic diversity of GBS isolates from different phylogenetic hosts and geographical regions. We have examined fish and dolphin GBS strains using phenotypic, serological typing and multilocus sequence typing (MLST) techniques and compared these to bovine and human GBS isolates. Studies were also conducted on infectivity of fish, dolphin, bovine and human GBS isolates in Nile tilapia, Oreochromis niloticus. A previously unreported fish capsular serotype, Ia, was discovered for tilapia isolates originating from Brazil, Israel and the U.S.A, and mullet, seabream and dolphin isolates from Kuwait. Serotype Ib was noted for other tilapia isolates from Brazil and Honduras. Sequence typing of isolates produced six sequence types (ST-7, ST-257, ST-258, ST-259, ST 260 and ST-261), the latter five ST¿s representing allelic designations and allelic combinations unique to the S. agalactiae MLST database. Kuwait isolates (Ia, ST-7), although largely unrelated to the majority of bovine and human GBS strains, appear to share a common ancestry. Kuwait GBS isolates shared the same allelic profile, sequence type and capsular serotype as that reported from human GBS strains from Japan (Ia, ST-7). Genomic diversity existed between Kuwait GBS isolates and those from other geographical areas. Tilapia GBS isolates from Brazil, Israel, Honduras and the U.S.A. are part of a clonal complex and are unrelated to bovine and human GBS, thus representing a distinct genetic population. In experimental studies using fish isolates from different geographical regions, a Brazil GBS tilapia isolate was significantly more pathogenic to Nile tilapia than non tilapia isolates from Israel and Kuwait. However, all fish isolates caused mortalities at doses between 101 and 106 CFU/fish. Bovine serotype Ia, II and NT GBS isolates of unknown MLST type were not found to be infective to Nile tilapia although a human GBS isolate caused mortality in Nile tilapia. These experimental infectivity studies indicate enhanced virulence of fish GBS isolates to fish regardless of geographical origin. Here we summarize findings from GBS genomic and infectivity studies from our laboratories.

Technical Abstract: Our laboratory has conducted multiple studies to investigate the genomic diversity of GBS isolates from different phylogenetic hosts and geographical regions. We have examined fish and dolphin GBS strains using phenotypic, serological typing and multilocus sequence typing (MLST) techniques and compared these to bovine and human GBS isolates. Studies were also conducted on infectivity of fish, dolphin, bovine and human GBS isolates in Nile tilapia, Oreochromis niloticus. A previously unreported fish capsular serotype, Ia, was discovered for tilapia isolates originating from Brazil, Israel and the U.S.A, and mullet, seabream and dolphin isolates from Kuwait. Serotype Ib was noted for other tilapia isolates from Brazil and Honduras. Sequence typing of isolates produced six sequence types (ST-7, ST-257, ST-258, ST-259, ST 260 and ST-261), the latter five ST¿s representing allelic designations and allelic combinations unique to the S. agalactiae MLST database. Kuwait isolates (Ia, ST-7), although largely unrelated to the majority of bovine and human GBS strains, appear to share a common ancestry. Kuwait GBS isolates shared the same allelic profile, sequence type and capsular serotype as that reported from human GBS strains from Japan (Ia, ST-7). Genomic diversity existed between Kuwait GBS isolates and those from other geographical areas. Tilapia GBS isolates from Brazil, Israel, Honduras and the U.S.A. are part of a clonal complex and are unrelated to bovine and human GBS, thus representing a distinct genetic population. In experimental studies using fish isolates from different geographical regions, a Brazil GBS tilapia isolate was significantly more pathogenic to Nile tilapia than non tilapia isolates from Israel and Kuwait. However, all fish isolates caused mortalities at doses between 101 and 106 CFU/fish. Bovine serotype Ia, II and NT GBS isolates of unknown MLST type were not found to be infective to Nile tilapia although a human GBS isolate caused mortality in Nile tilapia. These experimental infectivity studies indicate enhanced virulence of fish GBS isolates to fish regardless of geographical origin. Here we summarize findings from GBS genomic and infectivity studies from our laboratories.