Molecular and antimicrobial susceptibility profiling of atypical Streptococcus species from porcine clinical specimens

The Streptococcus species present broad phenotypic variation, making identification difficult using only traditional microbiological methods. Even though Streptococcus suis is the most important species for the worldwide swine industry, other Streptococcus species appear to be able to cause disease in swine and could represent a higher underestimated risk for porcine health. The aim of this study was to identify Streptococcus-like isolates by MALDI-TOF MS and 16S rRNA sequencing and further molecular and antibiotic susceptibility characterization of the atypical Streptococcus species capable of causing disease in swine. Fifty presumptive Streptococcus isolates from diseased pigs isolated from different Brazilian States between 2002 and 2014 were evaluated. Among the studied isolates, 26% were identified as Streptococcus hyovaginalis, 24% as Streptococcus plurianimalium, 12% as Streptococcus alactolyticus, 10% as Streptococcus hyointestinalis, and the remaining isolates belonged to Streptococcus henryi (6%), Streptococcus thoraltensis (6%), Streptococcus gallolyticus (6%), Streptococcus gallinaceus (4%), Streptococcus sanguinis (4%), and Streptococcus mitis (2%). The Streptococcus isolates were successfully identified by spectral cluster analysis and 16S rRNA sequencing with 96% of concordance between the techniques. The SE-AFLP analysis also supported Streptococcus species distinction and enabled further observation of higher genetic heterogeneity intra-species. The identified Streptococcus species presented variable MIC values to β-lactams, enrofloxacin and florfenicol, and high resistance rates to tetracyclines and macrolides, which appear to be directly related to the industry's antimicrobial usage and resistance selection.