Corynebacterium species and Streptococcus species are the most commonly isolated bacteria from clinically ill pet guinea pigs.

OBJECTIVE: To report the prevalence of bacterial isolates and associated antimicrobial susceptibility from samples obtained from clinically diseased pet guinea pigs (Cavia porcellus). METHODS: A retrospective, observational, quantitative study was performed to identify bacterial isolates of pet guinea pigs and antibiotic susceptibility. Medical records were reviewed for guinea pigs evaluated at a university teaching hospital between 2004 and 2023, from which aerobic or anaerobic bacterial cultures were obtained. RESULTS: A total of 112 bacterial isolates were cultured from 63 guinea pigs. The most cultured sites included abscesses and the urinary tract. The 3 most prevalent bacterial genera isolated were Streptococcus (21 of 112 [19%]), Corynebacterium (19 of 112 [17%]), and Prevotella (11 of 112 [11%]). The most isolated species was Corynebacterium renale (12 of 112 [11%]). Corynebacterium spp accounted for 53% (10 of 19) of all urinary tract isolates. Susceptibility of Corynebacterium spp towards commonly used oral antibiotics was 94% for doxycycline, 82% for azithromycin, 71% for enrofloxacin, and 65% for trimethoprim-sulfamethoxazole (TMS). Among all urinary tract isolates, only 50% were susceptible to TMS, and 59% were susceptible to enrofloxacin. Among oral antibiotics used in guinea pigs, Streptococcus spp were all susceptible to TMS and azithromycin. CONCLUSIONS: The 2 gram-positive bacterial genera Corynebacterium and Streptococcus were the most common isolates in this study, with C renale being the most common species overall and the predominant urinary tract isolate from the guinea pigs in this study. CLINICAL RELEVANCE: Enrofloxacin and TMS are often prescribed empirically for urinary tract infections in guinea pigs, yet resistance may be high. Therefore, culture and susceptibility testing should be performed whenever feasible.