Tigecycline (GAR-936) activity against Streptococcus gallolyticus (bovis) and viridans group streptococci

Viridans group streptococci including Streptococcus gallolyticus (formerly S. bovis) represent serious invasive pathogens often associated with endocarditis or sepsis among immunocompromised or cancer patients. Tigecycline (GAR-936), the first clinically studied glycylcycline, has a potent Gram-positive activity with a potential treatment option for these streptococcal infections. The studied collection (848 strains) included 100 isolates each of Streptococcus anginosus, Streptococcus constellatus, Streptococcus intermedius, Streptococcus mitis, Streptococcus oralis, Streptococcus salivarius, Streptococcus sanguis, and fewer strains of S. gallolyticus (98 strains) and Streptococcus mutans (50 strains). These strains were isolated from patients on 3 continents in the SENTRY Antimicrobial Surveillance Program and tested for susceptibility and interpreted by Clinical and Laboratory Standards Institute broth microdilution methods and criteria (≤0.25 μg/mL for tigecycline per US Food and Drug Administration). Penicillin susceptibility rates for the entire collection varied from 61% (S. sanguis) to 98% (S. constellatus), and macrolide susceptibility was also compromised (49–88%; average, 69%). Tigecycline was active against all isolates tested, in contrast to tetracycline resistance rates of 8–66%, and highest for S. gallolyticus. In conclusion tigecycline was quite active against bacteremic isolates of viridans group streptococci species and S. gallolyticus with an overall MIC90 at ≤0.06 μg/mL; the highest MIC was only 0.25 μg/mL.