Sequenciamento, montagem e comparação genômica entre linhagens de Streptococcus agalactiae ST-17

Abstract

S. agalactiae are important pathogenic bacteria that cause severe infections in humans, especially neonates. Serological methods have limitations, as they may fail to type an isolate due to lack of or low expression of capsular polysaccharide under the experimental conditions. Recently, several methods for typing of S. agalactiae based on PCR targeting genes in the cps operon has been published as alternatives for serology. The implantation of S. agalactiae capsular typing by multiplex PCR in the Laboratory of Molecular Biology and Physiology of Streptococci (LBMFE) was successful. Non-oncological human S. agalactiae strains presented capsular type (CT) III as the most prevalent (41.86%), while CTIa was frequently isolated (44%) in strains from cancer patients. In S. agalactiae strains recovered from mastitis bovine, CT II (48.28%) was predominant.The mechanism by which S. agalactiae ST-17 causes invasive infections than other STs is not well understood. In this study, we sequenced the first genome of a S. agalactiae ST-17 strain (GBS90356) isolated in Brazil. S. agalactiae GBS90356 ST-17 from CTIII was isolated from a fatal neonatal case of meningitis. The genome presented a size of 2.03 Mbp and a G+C content of 35.2%. S. agalactiae has 706 genes and an open pan-genome with a size of 5.020 genes, suggesting a high genomic plasticity of S. agalactiae. GIPSy software was used to identify 10 pathogenicity islands (PAIs) which corresponded to 17% of the genome size. IslandViewer4 corroborated with the prediction of five of these PAIs. The PAIs showed important virulence genes for S. agalactiae e.g. neu, cps, dlt, fbs, cfb, lmb. SignalP detected 20 proteins with signal peptides among the 352 proteins found in PAIs, which 60% were located in the SagPAI_5. The SagPAI_2 and 5 were partially detected in all ST-17 strains (n=6) studied. Moreover, we identified unique genes belonging to ST-17 strains, which can be related with the virulence during host-pathogen interactions. We provide evidence of high genomic plasticity in not usual pathogenic bacteria as S. agalactiae with small genome. PAIs comprise a large portion of the genome, indicating that the majority of virulence genes are involved in S. agalactiae pathogenicity process. Activity inhibition of β-hemolitic of GBS90356 reduced the adherence and invasion profiles, sugesting that β-hemolysin was required in the process of S. agalactiae dissemination in HUVEC. Morphological changes and signals of apoptose were validated during GBS90356-HUVEC interaction. All these findings suggest that the virulence of S. agalactiae could be related to high plasticity and the presence of the mobile genetic elements.