title: Molecular serotyping, virulence gene profiling and pathogenicity of Streptococcus agalactiae isolated from tilapia farms in Thailand by multiplex PCR.
abstract: OBJECTIVE
  This study aimed to biotype Streptococcus agalactiae isolated from tilapia farms in Thailand based on molecular biotyping methods and to determine the correlation between the serotype and virulence of bacteria. In addition to a biotyping (serotyping) technique based on multiplex PCR of cps genes, in this study, we developed multiplex PCR typing of Group B streptococcus (GBS) virulence genes to examine three clusters of virulence genes and their correlation with the pathogenicity of S. agalactiae. The epidemiology of S. agalactiae in Thailand was analysed to provide bacterial genetic information towards a future rational vaccine strategy for tilapia culture systems.
  
  
  RESULTS
  Streptococcus agalactiae were isolated from diseased tilapia from different areas of Thailand. A total of 124 S. agalactiae isolates were identified by phenotypic analysis and confirmed by 16S rRNA PCR. Bacterial genotyping was conducted based on (i) molecular serotyping of the capsular polysaccharide (cps) gene cluster and (ii) virulence gene profiling using multiplex PCR analysis of 14 virulence genes (lmb, scpB, pavA, cspA, spb1, cyl, bca, rib, fbsA, fbsB, cfb, hylB, bac and pbp1A/ponA). Only serotypes Ia and III were found in this study; serotype Ia lacks the lmb, scpB and spb1 genes, whereas serotype III lacks only the bac gene. Virulence tests in juvenile Nile tilapia demonstrated a correlation between the pathogenicity of the bacteria and their virulence gene profile, with serotype III showing higher virulence than serotype Ia. Epidemiological analysis showed an almost equal distribution in all regions of Thailand, except serotype III was found predominantly in the southern areas.
  
  
  CONCLUSIONS
  Only two serotypes of S. agalactiae were isolated from diseased tilapia in Thailand. Serotype Ia showed fewer virulence genes and lower virulence than serotype III. Both serotypes showed a similar distribution throughout Thailand.
  
  
  CONCLUSIONS
  We identified two major serotypes of S. agalactiae isolates associated with the outbreak in tilapia culture in Thailand. We developed multiplex PCR assays for 14 virulence genes, which may be used to predict the pathogenicity of the isolates and track future infections. Multiplex PCR typing of the GBS virulence genes was developed and might be further used to predict the pathogenicity of S. agalactiae.
authors.affiliation: Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok, Thailand.|Center for Advanced Studies for Agriculture and Food, Kasetsart University Institute for Advanced Studies, Kasetsart University, Bangkok, Thailand.
authors.forename: K
authors.initials: K
authors.lastname: Kannika
authors.affiliation: Fishery Science and Aquatic Resources, Faculty of Agricultural Technology, King Mongkut's Institute of Technology Ladkrabang, Prince of Chumphon Campus, Chumphon, Thailand.
authors.forename: D
authors.initials: D
authors.lastname: Pisuttharachai
authors.affiliation: Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok, Thailand.
authors.forename: P
authors.initials: P
authors.lastname: Srisapoome
authors.affiliation: Department of Veterinary Medicine, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand.
authors.forename: J
authors.initials: J
authors.lastname: Wongtavatchai
authors.affiliation: Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, Tokyo, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kondo
authors.affiliation: Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, Tokyo, Japan.
authors.forename: I
authors.initials: I
authors.lastname: Hirono
authors.affiliation: Center for Advanced Studies for Agriculture and Food, Kasetsart University Institute for Advanced Studies, Kasetsart University, Bangkok, Thailand.|Department of Biochemistry, Faculty of Science, Kasetsart University, Bangkok, Thailand.
authors.forename: S
authors.initials: S
authors.lastname: Unajak
authors.affiliation: Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok, Thailand.|Center for Advanced Studies for Agriculture and Food, Kasetsart University Institute for Advanced Studies, Kasetsart University, Bangkok, Thailand.
authors.forename: N
authors.initials: N
authors.lastname: Areechon
mesh_terms: D000293:Adolescent; D000818:Animals; D005398:Fisheries; D005838:Genotype; D006801:Humans; D060885:Multiplex Polymerase Chain Reaction; D012703:Serotyping; D013292:Streptococcus agalactiae / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D013785:Thailand; D017210:Tilapia / Q000382:microbiology*; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D037521:Virulence Factors
keywords: 
  Oreochromis niloticus
  ; 
  Streptococcus agalactiae
  ; Tilapia; pathogenicity; serotyping; virulence genes