Antimicrobial characterisation of solithromycin (CEM-101), a novel fluoroketolide: activity against staphylococci and enterococci

Solithromycin (CEM-101) is a novel fluoroketolide with high potency against Gram-positive and Gram-negative bacteria commonly associated with community-acquired respiratory tract infections and skin and skin-structure infections. In this study, solithromycin and comparator antimicrobials were tested against a contemporary collection of Staphylococcus aureus, coagulase-negative staphylococci, Enterococcus faecalis, Enterococcus faecium and other Enterococcus spp. collected in the SENTRY Antimicrobial Surveillance Program. Solithromycin was active against S. aureus [minimum inhibitory concentration for 50% of the organisms (MIC50) = 0.12 μg/mL] and was two-fold more active than telithromycin (MIC50 = 0.25 μg/mL). Solithromycin was more potent against meticillin (oxacillin)-susceptible S. aureus [MIC50 = 0.06 μg/mL and MIC for 90% of the organisms (MIC90) = 0.12 μg/mL) compared with meticillin (oxacillin)-resistant S. aureus (MIC50 = 0.12 μg/mL and MIC90 > 16 μg/mL). Solithromycin activity was reduced amongst heterogeneous vancomycin-intermediate S. aureus and vancomycin-resistant S. aureus (MIC50 > 16 μg/mL). Against strains with defined susceptibilities to erythromycin, clindamycin and telithromycin, solithromycin showed potent inhibition against all combinations (MIC50 = 0.06 μg/mL) except those with non-susceptibility to telithromycin (>2 μg/mL) (MIC50 > 16 μg/mL). The solithromycin MIC50 for E. faecium (1 μg/mL) was four-fold higher than the MIC50 for E. faecalis (0.25 μg/mL). In summary, solithromycin demonstrated high potency against many Staphylococcus and Enterococcus spp. isolated from contemporary infections worldwide.