An Exploration of Antibiotic Resistance in Zoonotic Streptococcus canis: From Susceptibility Testing to Genomic Profiling

Streptococcus canis, a zoonotic pathogen primarily associated with infections in companion animals, has recently been recognized as a cause of human infections. This study investigated the antibiotic resistance in S. canis, focusing on seven isolates obtained from previous cases submitted to the Connecticut Veterinary Medical Diagnostic Laboratory. Their identities were confirmed using phenotypic assays via the Omnilog PM System (Biolog Inc., Hayward, CA). Antibiotic susceptibility profiles were determined via the Kirby-Bauer Disk Diffusion Susceptibility Test, employing a panel of antibiotics commonly used against gram-positive bacteria as recommended by the Clinical & Laboratory Standards Institute (CLSI) for Veterinary Medicine. Bacterial DNA extraction was performed using Qiagen’s DNeasy Blood & Tissue Kit (Qiagen, Redwood City, CA), followed by high molecular weight DNA extraction using the Wizard® HMW Extraction Kit (Promega, Madison, WI). Next-generation sequencing (NGS) was accomplished by preparing libraries using Illumina DNA Prep Kits with Nextera Indexes (Illumina, San Diego, CA). Sequences were screened for determinants of antibiotic resistance. Eighty-six percent exhibited phenotypic resistance to tetracycline. Genes associated with tetracycline and macrolide resistance were detected using NGS. The detection of resistance genes suggests antibiotic resistance and potential zoonotic spillover. Therefore, understanding the antibiotic resistance patterns of the understudied S. canis is essential for monitoring its potential impact on human and animal health.