期刊
JOURNAL OF VETERINARY DIAGNOSTIC INVESTIGATION
卷 26, 期 4, 页码 488-495出版社
SAGE PUBLICATIONS INC
DOI: 10.1177/1040638714534237
关键词
Genetic diversity; molecular characteristic; Streptococcus agalactiae; tilapia; virulence gene profiling
资金
- Chulalongkorn University
- 90th Anniversary of Chulalongkorn University Fund (Ratchadapiseksomphot Endowment Fund)
- PhD Scholarship for Research Abroad (D-RSAB)
- Thailand Research Fund
- Office of the Higher Education Commission [MRG5080209]
Streptococcus spp. were recovered from diseased tilapia in Thailand during 2009-2010 (n = 33), and were also continually collected from environmental samples (sediment and water) from tilapia farms for 9 months in 2011 (n = 25). The relative percent recovery of streptococci from environmental samples was 13-67%. All streptococcal isolates were identified as S. agalactiae (group B streptococci [GBS]) by a species-specific polymerase chain reaction. In molecular characterization assays, 4 genotypic categories comprised of 1) molecular serotypes, 2) the infB allele, 3) virulence gene profiling patterns (cylE, hylB, scpB, lmb, cspA, dltA, fbsA, fbsB, bibA, gap, and pili backbone-encoded genes), and 4) randomly amplified polymorphic DNA (RAPD) fingerprinting patterns, were used to describe the genotypic diversity of the GBS isolates. There was only 1 isolate identified as molecular serotype III, while the others were serotype Ia. Most GBS serotype Ia isolates had an identical infB allele and virulence gene profiling patterns, but a large diversity was established by RAPD analysis with diversity tending to be geographically dependent. Experimental infection of Nile tilapia (Oreochromis niloticus) revealed that the GBS serotype III isolate was nonpathogenic in the fish, while all 5 serotype Ia isolates (3 fish and 2 environmental isolates) were pathogenic, with a median lethal dose of 6.25-7.56 log 10 colony-forming units. In conclusion, GBS isolates from tilapia farms in Thailand showed a large genetic diversity, which was associated with the geographical origins of the bacteria.
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