In vitro activity of the new ketolide ABT-773 against community acquired respiratory tract isolates and Viridans Streptococci.

A total of 230 isolates were collected from clinical specimens of patients attending five health centers of the Buenos Aires, Argentina. ABT-773 was compared to erythromycin, azithromycin and clindamycin against bacterial isolates responsible for community-acquired respiratory tract infections and viridans streptococci showing different resistance patterns. Time-kill curves were also performed against selected resistant isolates. All but one of the 105 pneumococcal isolates were susceptible to ABT-773. Among the erythromycin resistant S. pyogenes isolates, all the M type and inducible isolates were susceptible to ABT-773. ABT-773 showed excellent activity against macrolide, azalide, lincosamide (MAL) inducible S. aureus producers but was inactive against constitutive producers. ABT-773 activity against viridans streptococci was also excellent.ABT-773 exerted bactericidal activity against selected isolates of S. pneumoniae, M. catarrhalis and H. influenzae, however, it was only bacteriostatic against methicillin-susceptible S. aureus.