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

Abstract

Group B Streptococcus (GBS) is a major pathogen of humans and aquatic species. Fish have recently been recognized as the source of severe invasive foodborne GBS disease, caused by sequence type (ST) 283, in otherwise healthy adults in Southeast Asia. Thailand and Vietnam are among the major aquaculture producers in Southeast Asia, with GBS disease reported in fish as well as frogs in both countries. Still, the distribution of potentially human-pathogenic GBS in aquaculture species is poorly known. Using 35 GBS isolates from aquatic species in Thailand collected from 2007 to 2019 and 43 isolates from tilapia collected in Vietnam in 2018 and 2019, we have demonstrated that the temporal, geographical, and host-species distribution of GBS ST283 is broader than previously known, whereas the distribution of ST7 and the poikilothermic lineage of GBS are geographically restricted. The gene encoding the human GBS virulence factor C5a peptidase, scpB, was detected in aquatic ST283 from Thailand but not in ST283 from Vietnam or in ST7 from either country, mirroring current reports of GBS strains associated with human sepsis. The observed distribution of strains and virulence genes is likely to reflect a combination of spill-over, host adaptation through the gain and loss of mobile genetic elements, and current biosecurity practices. The plastic nature of the GBS genome and its importance as a human, aquatic, and potentially foodborne pathogen suggests that active surveillance of GBS presence and its evolution in aquaculture systems may be justified.

Revisiting typing systems for group BStreptococcus(GBS) prophages: an application in prophage detection and classification in GBS isolates from Argentina

“…The prevalence of GBS isolates carrying at least one prophage and the average number of prophages per isolate found in our dataset correlates with previous reports on prophage content in GBS [11,13,15,35,36]. Our results also aligned with the integrase type and CC associations reported previously by Crestani [16].…”

Dispersal history and bidirectional human-fish host switching of invasive, hypervirulent Streptococcus agalactiae sequence type 283

“…Antimicrobial resistance and virulence factor genes were lost more frequently than gained throughout the evolutionary history of ST283. An active rate of gene change in ST283 is consistent with GBS as a pathogen under evolutionary pressure, with recombination and mobile elements contributing to a shifting genome composition generating new, niche-adapted lineages [ 11 , 23 , 26 ]. Gene loss may facilitate rapid adaptation to the functional requirements of host suitability, for example, reducing the metabolic burden of gene expression, enhancing fitness and conferring a selective advantage in such niche-adapted lineages [ 23 ].…”

“…The lmb and scpB genes were positively correlated, and lmb was correlated with isolates originating from human hosts, pointing to a possible complementary role for these genes in invasive human infections. Loss of human-associated virulence factor genes in transitioning to fish hosts could explain the stochastic pattern of foodborne fish consumption-associated ST283 outbreaks: within a cyclical human-to-fish spillover and fish-to-human spillback context, the loss of GBS genes critical for human invasive disease may limit potential for spillback to result in human clinical illness [ 11 ].…”

“…In aquaculture, GBS is responsible for substantial fish mortality and production loss [ 9 ], and both ST283 and a single locus variant (ST491) have been reported from diseased fish in southeast Asia [ 10 , 11 ]. Isolation of ST283 in 2016 from fish in Brazil indicates this strain may currently be undergoing further global dissemination [ 12 ].…”