Large-scale genomic analyses reveal the population structure and evolutionary trends of Streptococcus agalactiae strains in Brazilian fish farms

Abstract

Streptococcus agalactiae is a major pathogen and a hindrance on tilapia farming worldwide. The aims of this work were to analyze the genomic evolution of Brazilian strains of S. agalactiae and to establish spatial and temporal relations between strains isolated from different outbreaks of streptococcosis. A total of 39 strains were obtained from outbreaks and their whole genomes were sequenced and annotated for comparative analysis of multilocus sequence typing, genomic similarity and whole genome multilocus sequence typing (wgMLST). The Brazilian strains presented two sequence types, including a newly described ST, and a non-typeable lineage. The use of wgMLST could differentiate each strain in a single clone and was used to establish temporal and geographical correlations among strains. Bayesian phylogenomic analysis suggests that the studied Brazilian population was co-introduced in the country with their host, approximately 60 years ago. Brazilian strains of S. agalactiae were shown to be heterogeneous in their genome sequences and were distributed in different regions of the country according to their genotype, which allowed the use of wgMLST analysis to track each outbreak event individually.

Transcriptome and Proteome of Fish-Pathogenic Streptococcus agalactiae Are Modulated by Temperature

“…Nevertheless, genes/proteins that play a key role in pathogenicity were detected with differential abundance among the temperatures. Although the fish-adapted GBS strains had evolved in divergent branch from mammalian GBS isolates (Barony et al, 2017 ), several genes are shared among piscine and mammalian strains (Rosinski-Chupin et al, 2013 ; Kawasaki et al, 2018 ), including those identified as differentially expressed in our study. Therefore, upregulation at 32°C of proteins IagA, CpsB and cAMP factor may be important for the onset of streptococosis in tilapia during the warmer months.…”

“…The isolate selected for these analyses was the GBS SA53 strain. This strain was previously isolated from diseased Nile tilapia in Brazil (Mian et al, 2009 ) and belongs to ST-260, one of the most frequently identified genotypes in Latin America (Evans et al, 2008 ; Delannoy et al, 2013 ; Godoy et al, 2013 ; Barato et al, 2015 ; Barony et al, 2017 ). SA53 belongs to a group of fish-adapted genotypes that descend from a single branch unlike human GBS strains, and are going through reductive genome evolution (Barony et al, 2017 ).…”

“…This strain was previously isolated from diseased Nile tilapia in Brazil (Mian et al, 2009 ) and belongs to ST-260, one of the most frequently identified genotypes in Latin America (Evans et al, 2008 ; Delannoy et al, 2013 ; Godoy et al, 2013 ; Barato et al, 2015 ; Barony et al, 2017 ). SA53 belongs to a group of fish-adapted genotypes that descend from a single branch unlike human GBS strains, and are going through reductive genome evolution (Barony et al, 2017 ). Its LD 50 was not previously determined but isolates obtained from diseased fish have been demonstrated as highly virulent in experimental assays with Nile tilapia, with an LD 50 ranging from 10 1 to 10 5 cfu mL −1 (Mian et al, 2009 ; Evans et al, 2015 ).…”

“…The strain was selected from a culture collection at the National Reference Laboratory for Aquatic Animal Diseases (AQUACEN), and belongs to the most frequent genotype occurring in Latin America (Evans et al, 2008 ; Godoy et al, 2013 ; Barato et al, 2015 ). The complete genome sequence is available in GenBank (accession number CP019802.1; Barony et al, 2017 ). The strain was streaked on 5% sheep blood agar and incubated at 28°C for 48 h. Colonies were then inoculated in triplicate cultures of 100 mL BHI broth (Brain Heart Infusion broth, Himedia, Mumbai, India) with 0.05% (v/v) Tween 80 (BHIT), and incubated at 32 or 22°C under low agitation.…”

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

“…Among them, capsular serotypes Ⅲ, Ia, Ib and Ⅴ are the most common in humans in China (Jiang et al, ; Wang et al, ). However, in the past decade, GBS strains of the Ia, Ib and III serotypes were shown to predominate in fish infections, and serotype Ia and Ib strains are mainly responsible for tilapia streptococcosis (Barato, Martins, Melo‐Cristino, Iregui, & Ramirez, ; Barony et al, ; Li et al, ). In China, an epidemiological study showed that the serotype Ia GBS strain is the most frequent serotype in tilapia infection, accounting for >90% of all GBS isolates (Li et al, ).…”