Phenotype, genotype and pathogenicity of Streptococcus agalactiae isolated from cultured tilapia (Oreochromis spp.) in Taiwan

Abstract

Tilapia (Oreochromis spp.) is globally used as an aquaculture fish species due to its high growth rate and disease resistance. However, it faces an increased risk of streptococcosis. Streptococcus agalactiae, also known as group B streptococcus (GBS), is the most important tilapia pathogen in Asia. Studies of Str. agalactiae infection in Taiwan are still unclear. Thus, this study aimed to explore the phenotype, genotype and pathogenicity of Str. agalactiae isolated from cultured tilapia in Taiwan in 2016–2018. The analysis revealed that 85% of the strains displayed β‐haemolysis and 15% showed γ‐haemolysis, with the same capsule level, and were positive for the CAMP test. The Rapid ID 32 Strep test showed a similarity of Rapid ID 32 Strep is more than 99.5% to GBS. Genotypic distribution by molecular serotyping detected only serotype Ia from all isolates, despite the regional differences. Pulsed‐field gel electrophoresis (PFGE) was categorized into 3 and 10 clusters by restriction enzymes SmaI and ApaI, respectively. Virulence genes and antimicrobial resistance genes presented the same profile in all isolates. The challenge test with 106 CFU/fish (LD50), administered intraperitoneally, showed that the β‐haemolysis strains had a higher mortality rate than γ‐haemolysis, although they were from the same cluster from PFGE, year and region.

Genotype and virulence gene analyses of Bacillus cereus group clinical isolates from the Chinese softshell turtle (Pelodiscus sinensis) in Taiwan

“…piscicida was first reported in 1963 (Snieszko et al., 1964) and has been reported to infect various aquatic animal species, such as striped bass ( Morone saxatilis ) (Snieszko et al., 1964), yellowtail ( Seriola quinqueradiata ) (Kubota et al., 1970) and cobia ( Rachycentron canadum ) (Pham et al., 2020). Thus, pathogens that have been prevalent for a long time and possess greater host diversity have a higher possibility of genotypic and phenotypic diversity than emerging pathogens (Pham et al., 2020; Sudpraseart et al., 2021; Tsai et al., 2012).…”

“…DNA from all selected isolates was extracted as described previously (Sudpraseart et al., 2021), with few modifications. Briefly, the bacteria were harvested and washed with PBS.…”

“…The 57 Bcg isolates were streaked onto the brain–heart infusion agar and incubated at 25°C for 24 hr. PFGE was performed as previously described (Sudpraseart et al., 2021), with a few modifications. Briefly, Bcg isolates were harvested and suspended in PBS and adjusted to an optical density of 1.5 at 610 nm.…”

“…The 57 Bcg isolates were streaked onto the brain-heart infusion agar and incubated at 25°C for 24 hr. PFGE was performed as previously described (Sudpraseart et al, 2021), with a few modifications.…”

Prevalence, antimicrobial susceptibility, and genotyping of Streptococcus agalactiae in Tilapia fish (Oreochromis niloticus) in Egypt

“…The severity of the disease produced may be attributable to factors such as its virulence marker and water temperature [ 12 , 13 ]. Virulence genes facilitate the ability of the pathogen to cause disease.…”