In this study, five capsular types (Ia, II, III, V, IX) were identified and, except for type IX, all are frequently associated with GBS infections worldwide [3, 7–9, 20, 21]. The serotypes identified in this study were also detected in different surveys that were performed with Brazilian isolates among pregnant and non-pregnant adults. In those studies, the serotypes Ib [10, 11, 31] IV [11, 12], VI  and VIII  were also identified. The genetic diversity of GBS isolates were assessed by MLVA , which is based on the amplification of polymorphic tandem repeat sequences (also called VNTR-Variable Number of Tandem Repeats). It is easy to use, displays shorter time of execution, can be applied to a small or large numbers of isolates and has been employed successfully for the typing of different bacteria species. In addition, it has higher discriminatory power than Multi Locus Sequencing Typing (MLST), the reference method for genotyping Streptococcus spp. [32, 33]. The diversity index obtained with MLVA for this bacterial population was 0.84, lower than observed by others [32, 33]. However, despite the close relatedness of several isolates, as judged by the capsular type and presence of pili islands, this genotyping scheme discriminated the GBSs in this study. In fact, a total of 15 different genetic groups were identified among these isolates. SAG7, SAG21 and SAG22 presented higher degree of the variation in the number of repeats among the isolates, corroborating the data of Haguenoer et al. . Although no statistical correlation was performed, it was observed that isolates belonging to the capsular type II were confined to MT1, indicating that the genetic background of this serotype may be well conserved. Higher number of isolates may corroborate these findings.
All isolates were susceptible to the antimicrobials evaluated in this study, except erythromycin and clindamycin. Although it was not an epidemiological investigation, the overall rate of erythromycin resistance among the isolates analyzed was 19.3%. Previous epidemiological and bacterial collection data from Brazilian GBS isolates showed that erythromycin resistance ranged from 4 to 14% [10–13]. A higher incidence rate was observed in other regions, where erythromycin resistance up to 40% among GBS isolates was detected in Europe  and USA [3, 9]. In this study, resistance to both erythromycin and clindamycin was observed in GBS isolates of capsular types III and V, whereas the isolates displaying resistance only to erythromycin were exclusively found in the Ia capsular type. Similar results were previously obtained by other authors [3, 10]; however, resistant isolates for both antimicrobials were also observed among the Ib, II, IV, VI and VIII capsular serotypes [3, 34]. The mechanisms of macrolide resistance are mediated by ermA, ermB and mefA/E, and the distribution of these genes among GBS isolates in this study were in accordance with the macrolide-resistance phenotypes. These results were also observed by others [10–13]. The increasing numbers of isolates showing macrolide resistance together with the description of reduced susceptibility to penicillin emphasize the need for continued monitoring of antimicrobial susceptibility profile to identify the emergence of resistance among GBS isolates.
Data of the potential virulence of GBS isolates from Brazil are limited. Three genomic islands encoding the structurally distinct types of pili (PI-1, PI-2a and PI-2b) were identified in GBS. These pili are organized in two different loci, where PI-2a and PI-2b are located at the same chromosomal locus, with these being mutually exclusive . To our knowledge, this is the first study describing the prevalence of the pilus island in Brazilian GBS isolates, and at least one pilus type was detected among the isolates, supporting their use as an antigen for vaccine development. The combination of PI-1 and PI-2a was the most prevalent among the GBS isolates, and this result is in agreement with previous reports [21, 36]. In addition, the presence of this combination was correlated with maternal colonization and invasive disease in adults .
The cyl locus of GBS consists of a cluster of twelve genes , and some of them can modulate cylE expression and secretion , which is crucial for β-H/C activity. This toxin can promote the invasion of epithelial or endothelial cells , facilitate their persistence and intracellular survival , and enable their dissemination at host sites. Besides, acting as a virulence factor, CylE is associated with the characteristic translucent halo around GBS colonies grown on blood agar plates and production of orange carotenoid pigment on specific chromogenic agar, features that are used for presumptive identification of S. agalactiae. In this study, four GBS isolates were non-hemolytic and simultaneously non-pigment producers. Indeed, approximately 3% of GBS isolates are non-hemolytic , emphasizing the need to develop new methods that combine identification and detection of antimicrobial resistance for these bacteria.
The role of hyaluronidase in the pathogenesis of GBS infections is still unclear, but it is postulated that this enzyme can facilitate the invasion and dissemination of GBS during infection. The expression of this enzyme has been associated with GBS isolated from invasive infections ; however, hyaluronidase activity has also been detected in commensal GBS isolates from women’s genital tract .