Submitted to: International Symposium on Talipia in Aquaculture
Publication Type: Abstract only
Publication Acceptance Date: 6/15/2008
Publication Date: 10/12/2008
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. 8th International Symposium on Talipia in Aquaculture. Cairo, Egypt October 12-14, 2008. p. 109. Interpretive Summary:
Technical Abstract: Streptococcus agalactiae, the Lancefield group B Streptococcus (GBS), has a broad host range and can be pathogenic to numerous animals, including fish. GBS is most recognized for causing cattle mastitis and human neonatal meningitis, it also causes fatal meningo-encephalitis in fish. We investigated the genomic diversity of GBS isolates from different phylogenetic hosts and geographical regions. We examined fish and dolphin GBS strains using serological typing and multilocus sequence typing (MLST) molecular 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 infectivity studies, tilapia GBS isolates (non-ST-7) regardless of geographical origin, and isolates from mullet, seabream and dolphin (serotype Ia, ST-7) caused experimental disease signs and mortality in Nile tilapia. Likewise the human GBS isolate associated with neonatal infections in Japan caused experimental disease signs and mortality in Nile tilapia. Bovine serotype Ia, II and NT GBS isolates of unknown MLST type were not found to be infective to Nile tilapia. Results suggest that GBS isolates from different aquatic animals irrespective of serotype and MLST type and mammalian isolates of the same serotype and MLST are capable of infecting tilapia.