Relações clonais, genes de virulência e patogenicidade dos Streptococcus agalactiae isolados de peixes

Abstract

Streptococcus agalactiae is one of the most important pathogen for human newborns and cultivated fish. It is the principal health problem for tilapia farming, responsible for high economic losses worldwide. Although, the diversity of S. agalactiae isolates and main virulence traits in fish infections is poorly understood. The goals of this work were to access the genetic patterns of fish isolates of S. agalactiae, by capsular serotype and MLST. Additionally, the relationship between virulence gene profiles and in vivo pathogenicity were addressed. Forty-six isolates from Nile tilapia and Amazon catfish were screened to the virulence genes: bac, bca, bibA, cfb, cylE, hylB, gbs2018-6, iagA, lmb, scpB, fbsA and fbsB, by PCR. The molecular capsular type and ST were determined by multiplex PCR and MLST analysis, respectively. The isolates were all positive for iagA, cfb, gbs2018-6, fbsA and fbsB and negative for bac, bibA, bca and scpB. Variable results were verified for lmb, hylB and cylE. Two capsular types (Ia and Ib), four ST (103, 260, 552 and 553) and six virulence gene profiles (I to VI) were found. Two new ST and ST 103 associated with fish disease were firstly described here. This work shows that (i) fish strains of S. agalactiae is a diverse population; (ii) they are highly virulent and show an association between the profile of virulence genes and the pathogenicity in vivo; (iii) there is no association between virulence, ST and capsular serotype.