Carumonam's in-vitro activity against gram-negative bacteria and its stability to their beta-lactamases

The in vitro activity of the novel monobactam carumonam (RO17-2301) was evaluated on 311 gram-negative clinical isolates in comparison to aztreonam, cefotaxime, ceftazidime, cefotetan and ceftriaxone. Carumonam showed an antibacterial potency equal to or higher than any other reference compound; in particular it was the most effective against Proteus indole positive and Klebsiella sp. Its antipseudomonal activity was comparable to that of ceftazidime and it showed, together with aztreonam, the highest activity against the Citrobacter, Enterobacter and Escherichia coli isolates. The minimal inhibitory concentrations performed on permeability altered organisms indicated that carumonam has a penetration rate comparable to aztreonam and higher than cefotetan and ceftriaxone. Carumonam demonstrated excellent stability to chromosomal and plasmid-mediated beta-lactamases and that correlated with its antibacterial activity against the producing strains and inoculum size effect.