Phenotypic and genotypic characterization of Streptococcus spp. isolated from tilapia (Oreochromis spp.) cultured in river‐based cage and earthen ponds in Northern Thailand

Abstract

Streptococcus spp. are major pathogenic bacteria associated with massive mortality in tilapia. This study investigated the phenotypic and genotypic characterization of Streptococcus agalactiae (GBS) and Streptococcus iniae (S. iniae) isolated from tilapia in river-based floating cage and earthen pond farms in northern Thailand. Isolates were identified by biochemical and molecular analyses. Capsular typing, enterobacterial repetitive intergenic consensus polymerase chain reaction and multilocus sequence typing were performed to investigate the genetic relatedness. Six and one isolates were confirmed as GBS and S. iniae, respectively. All Streptococcus spp. isolates were obtained from 4 river-based cage farms (4/33), while samples collected from earthen pond farms (N = 28) were negative for streptococcosis. All GBS with serotype Ⅲ and sequence type (ST) 283 was observed. The β-haemolytic GBS isolates were resistant to five antimicrobials, while the S. iniae was susceptible to all antimicrobials. This study indicates both GBS and S. iniae are the major bacterial pathogens responsible for streptococcosis infection in farmed tilapia of northern Thailand with GBS as dominant species. This survey highlights that the river-based cage farms seriously impact on the healthy development of the tilapia industry. K E Y W O R D Searthen pond farm, northern Thailand, river-based cage farm, Streptococcus spp., tilapia ACK N OWLED G EM ENTS

Geographical, Temporal and Host-Species Distribution of Potentially Human-Pathogenic Group B Streptococcus in Aquaculture Species in Southeast Asia

“…Wastewater and pond water can be reservoirs of GBS [45,46] and exposure of aquatic animals via contaminated surface water has been described on multiple occasions [17,47]. Interestingly, ST283 was commonly found in river cage-based tilapia farms in Thailand but not in earthen pond systems [48]. There is no evidence yet of ST283 in cage-based tilapia farms along the Perfume River.…”

Trial Evaluation of Protection and Immunogenicity of Piscine Bivalent Streptococcal Vaccine: From the Lab to the Farms

“…Based on our research on S. agalactiae characterization, we could isolate 2 major serotypes, serotype Ia and serotype III, that caused disease in tilapia, which was similar to the surveillance in other countries in SE Asia such as Malaysia [ 17 , 21 , 22 , 37 , 38 , 39 ]. Based on our findings, both serotypes showed similar distribution throughout Thailand during 2012–2014; however, it was found that serotype III exhibited higher virulence than serotype Ia [ 21 ].…”

“…The outbreaks of streptococcosis have been related to environmental factors, including warm water temperatures, increased ammonia levels, and low dissolved oxygen [ 11 ]. S. agalactiae infections in tilapia have been reported in global aquaculture in different continents, especially Asia, including Thailand [ 17 , 18 , 19 , 20 , 21 , 22 ], Malaysia [ 23 , 24 , 25 , 26 , 27 ], Indonesia [ 28 , 29 ], Philippines [ 30 ], and China [ 31 , 32 , 33 , 34 ]. Importantly, the emergence of streptococcosis disease can take place anytime during tilapia farming, which may lead to the risk of disease distribution and loss of tilapia production if disease prevention and control are not well managed.…”

Enterogyrusspp. (Monogenea: Ancyrocephalinae) andAeromonas jandaeico‐infection associated with high mortality following transport stress in cultured Nile tilapia

“…(Dong et al., 2017; Raj et al., 2019), Streptococcus spp. (Chideroli et al., 2017; Niu et al., 2020), Flavobacterium spp. (Dong et al., 2015), Edwardsiella spp.…”