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

Culture and susceptibility testing is essential for guinea pig UTIs, as TMS and enrofloxacin resistance rates are high.

This retrospective observational study evaluated bacterial isolates and antimicrobial susceptibility patterns from clinically ill pet guinea pigs (Cavia porcellus) examined at a university teaching hospital between 2004 and 2023. A total of 112 bacterial isolates were recovered from 63 guinea pigs, with abscesses and the urinary tract representing the most common culture sites. The three most frequently isolated genera were Streptococcus (19%), Corynebacterium (17%), and Prevotella (11%). Corynebacterium renale was the single most common species identified (11% of all isolates) and accounted for 53% of urinary tract isolates. Antimicrobial susceptibility testing revealed that Corynebacterium spp. were most susceptible to doxycycline (94%), followed by azithromycin (82%), enrofloxacin (71%), and trimethoprim-sulfamethoxazole (TMS; 65%). Of clinical concern, among all urinary tract isolates, susceptibility to TMS was only 50% and to enrofloxacin only 59%—two antibiotics commonly prescribed empirically for urinary tract infections (UTIs) in guinea pigs. Streptococcus spp. demonstrated 100% susceptibility to both TMS and azithromycin. These findings highlight a potentially significant gap between empirical antibiotic selection and actual susceptibility profiles, particularly for urinary tract infections. The authors emphasize that culture and susceptibility testing should be performed whenever clinically feasible to guide appropriate antimicrobial therapy and reduce the risk of treatment failure in this species.

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