Prevalence and antimicrobial susceptibility of Streptococcus equi isolated from horses in Santa Catarina state, Southern Brazil.

The objective of this study was to determine the prevalence of Streptococcus equi (S. equi subsp equi and S. equi subsp zooepidemicus) in the state of Santa Catarina and evaluate the antimicrobial susceptibility of the isolates. For this, 420 nasal swab samples were collected from randomly selected horses. Isolation and phenotypic characterization of the bacteria were performed by sowing on 5% sheep blood agar, followed by analysis of morphotinctorial characteristics and biochemical analysis. To differentiate the main beta-hemolytic Streptococcus in horses, the fermentation profiles of the sugar's lactose, maltose, sorbitol, and trehalose were used, which were confirmed at the subspecies level by the PCR technique. The antimicrobial susceptibility panel was defined by the disk diffusion method, testing 13 antimicrobials from ten different classes, all regularly used in equine medical clinics, followed by the calculation of the multiple antimicrobial resistance index. Ten strains of S. equi were isolated, with a prevalence of 2.38% (10/420). Of the total positive samples, 3% (3/10) were confirmed as belonging to S. equi subsp equi and 70% (7/10) were confirmed as belonging to S. zooepidemicus. Multidrug resistance was observed in 60% (6/10) of isolates. The antimicrobial with the greatest resistance was clindamycin with 70% (7/10), followed by beta-lactams, with 40% (4/10) resistance to penicillin and 30% (3/10) to ceftiofur. The isolates were 100% (10/10) sensitive to gentamicin, chloramphenicol, levofloxacin, and vancomycin. This was the first study carried out in the state, and based on these data, it can be said that Santa Catarina has a low prevalence of S. equi and the presence of multi-resistant strains of S. equi was confirmed in the equine herd in Santa Catarina.