In vitro activity of ABT773, a new ketolide derivative exhibiting innovative microbiological properties against well-characterised antibiotic resistant pathogens in Italy.

The in vitro activity of ABT773, a new ketolide, was assessed against a collection (518) of well-characterised Gram-positive and Gram-negative pathogens and compared with that of other appropriate drugs. ABT773 was active (MIC-90=0.03 mg/l) against the staphylococci tested which included macrolide-resistant but clindamycin susceptible organisms. Streptococcus pneumoniae, S. pyogenes and S. agalactiae were also inhibited (MIC-90 range: <0.0075-0.5mg/l) irrespective of their antibiotic resistance phenotype. Enterococcus faecalis was sensitive to ABT773 with the exception of VanA mutants. E. faecium showed poor susceptibility to ABT773. The activity of the new ketolide against Haemophilus influenzae and Moraxella catarrhalis was comparable with that of the most potent drugs tested. ABT773 displays the characteristics of a promising agent that deserves to be introduced as the empirical therapy of infections caused by the bacterial species tested here, even if they are multiply resistant.