Antimicrobial resistance profiling of Streptococcus suis isolated from neurological cases in Chilean pigs

Streptococcus suis is an important swine pathogen and an emerging zoonotic bacterium, with multidrug-resistant (MDR) strains representing an increasing concern for both animal and public health. This report describes the pathological findings and antimicrobial susceptibility profiles of MDR S. suis isolates recovered from the central nervous system of two pigs from a commercial swine farm in south-central Chile. Brain and spinal cord samples were examined by histopathology and microbiological culture, followed by bacterial identification and antimicrobial susceptibility testing using an antibiogram and minimum inhibitory concentration (MIC) analysis. Histopathological examination revealed non-suppurative inflammatory lesions characterized by mononuclear perivascular cuffing, consistent with meningoencephalomyelitis and myelitis. S. suis was isolated from the brain and/or spinal cord of both pigs. MIC testing demonstrated resistance to spectinomycin, ampicillin/amoxicillin, ceftiofur, penicillin, florfenicol, enrofloxacin, clindamycin, tilmicosin, tulathromycin, tylosin tartrate, tiamulin, sulfadimethoxine, trimethoprim/sulfamethoxazole, oxytetracycline, and chlortetracycline, indicating an MDR phenotype. Both isolates remained susceptible to gentamicin, while variable susceptibility was observed for danofloxacin, neomycin, tulathromycin, tiamulin, and trimethoprim/sulfamethoxazole. To the authors' knowledge, this is the first report of MDR S. suis associated with neurological disease in pigs from Chile. These findings provide additional information on the antimicrobial susceptibility of S. suis in Chile and support the need for broader antimicrobial resistance surveillance under a One Health framework, as well as the prudent use of antimicrobials in swine production.