Molecular characterization and virulence gene profiling of pathogenic Streptococcus agalactiae populations from tilapia (Oreochromis sp.) farms in Thailand

Abstract

Abstract. 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.

Naturally concurrent infections of bacterial and viral pathogens in disease outbreaks in cultured Nile tilapia (Oreochromis niloticus) farms

“…In theory, the floating cages culture system, where the fish are naturally exposed to various potential pathogens, is predictably infected by multiple (Ariel and Owens, 1997;McGrogan et al, 1998;Figueiredo et al, 2005;Olivares-Fuster et al, 2008;Dong et al, in press;Kayansamruaj et al, 2014a;Kayansamruaj et al, 2014b). In contrast, A. veronii, P. shigeloides and V. cholerae are not welldescribed fish pathogens and have been identified as foodborne pathogens that could present a serious issue to consumer health (Joseph et al, 1991;Nadirah et al, 2012;Chen et al, 2013;Chen et al, 2014;Nguyen et al, 2014).…”

“…Hemolysis has been considered as an important virulent factor of S. agalactiae (Olivares-Fuster et al, 2008;Kayansamruaj et al, 2014b). Previous studies revealed that a high temperature ( A C C E P T E D M A N U S C R I P T A C C E P T E D M A N U S C R I P T A C C E P T E D M A N U S C R I P T…”

“…The reality of disease outbreaks in cultured farms may in all probability be caused by multiple pathogen infections. Previously, some important pathogens devastating tilapia within intensively produced systems were reported, such as Streptococcus agalactiae (Olivares-Fuster et al, 2008;Kayansamruaj et al, 2014a;Kayansamruaj et al, 2014b), Flavobacterium columnare (Figueiredo et al 2005; press-a,b), Francisella sp. (Soto et al, 2009;Jeffery et al, 2010;Leal et al, 2014), Edwardsiella spp.…”

Aeromonas jandaei and Aeromonas veronii caused disease and mortality in Nile tilapia, Oreochromis niloticus (L.)

“…; Kayansamruaj et al . ); francisellosis caused by Francisella noatunensis subsp . orientalis (Soto et al .…”

Capsular polysaccharide of Streptococcus agalactiae is an essential virulence factor for infection in Nile tilapia (Oreochromis niloticus Linn.)

“…Virulence‐associated factors including those driving bacterial adhesion and colonization (Lmb, DltA, BibA, FbsA, FbsB and pili), bacterial invasion (HylE, CspA, and Gap), immune evasion (CylE, CpsA, ScpB and sialic acid) and toxicity (CylE, HylB and Cfb) can promote GBS entry into host cells and facilitate the intracellular survival and spread of GBS (Kayansamruaj, Pirarat, Katagiri, Hirono, & Rodkhum, ; Shabayek & Spellerberg, ; Udo, Boswihi, & Al‐Sweih, ; Zhang et al, ). Additionally, the capsule covers the outer layer of GBS strains, which is mainly composed of the capsular polysaccharide (CPS).…”