Streptococcus suis remains an important challenge for the worldwide swine industry. Considering that Brazil is a major pork producer and exporter, proper monitoring of the pathogen and resistance rates are required. We present here the characterization of Brazilian S. suis strains isolated over a 15 year period by pulsed-field gel electrophoresis (PFGE) typing, capsular, virulence, and antimicrobial resistance profiling. Serotype prevalence revealed a predominance of serotype 2/ 1 2 followed by 3, 7, 1/14, 6, 8, 18, 28, and 27; the latter had not yet been reported in Brazil. Resistance profiling enabled the differentiation of nine profiles presenting resistance to three and up to eight antimicrobial classes. Even though an association between the most resistant strains and isolation year starting from 2009 was observed, a high frequency of multidrug-resistant strains isolated from 2001 to 2003 was also detected. This suggests that despite the isolation period, S. suis strains already presented high resistance selection pressure. A slight association of serotype 2/ 1 2 with some virulence profiles and PFGE pulsotypes was also identified. Nevertheless, no clonal dispersion or persistency of clones over the analyzed years and herds was detected.Pathogens 2020, 9, 31 2 of 15 shown that serotypes 20, 22, 26, 32, 33, and 34 do not belong to this species and should be classified as other bacterial species [6,7]. Moreover, novel nine capsular polysaccharide synthesis (cps) loci (NCLs) of non-typable S. suis strains have been identified based on DNA sequencing. Therefore, strict S. suis species currently comprise 38 serotypes [8].Among the virulence factors that have already been characterized in S. suis, most studied so far are the capsule, muramidase-released protein (MRP), the extracellular factor (EF), hemolysins including suilysin (SLY), plasminogen receptors, and arginine deiminase (arcA) [9].Considering antimicrobial susceptibility of S. suis strains, recent studies have described increases in resistance rates to some antimicrobial classes. Resistance to lincosamides and macrolides has been increasing, both for pigs and human strains, and resistance to sulfonamides and tetracycline showed high prevalence [8]. Resistance to cephalosporin was already described in Europe and China, but resistance prevalence to penicillin, ampicillin, and ceftiofur remains low in most countries [8,10].Emergence of multidrug resistant S. suis strains has also been described in humans and pigs, including asymptomatic animals, with highlight for the Asian epidemic clones [8]. Phenotypic and genetic studies suggest that swine may be reservoirs for the spread of antibiotic-resistant S. suis strains, which demands attention for the public health risk [8].Brazil is a major producer and exporter of pork, occupying for several years the fourth place as producer and exporter in the world [4]. This position demands attention to swine health issues. Currently, special efforts are required to reduce antimicrobial usage and monitor resistance rates ...
