[Evaluation of bactericidal activity of cefpirome-aminoglycoside combination against Pseudomonas aeruginosa strains with intermediate sensitivity to cefpirome and in various phenotypes of beta-lactam resistance].

The bactericidal activity of cefpirome (CPO)-aminoglycoside (AG) combination was assessed by a kinetic time-kill method against 8 strains of Pseudomonas aeruginosa showing intermediate susceptibility to cefpirome (MICS: 8-32 mg/l). Six strains had an acquired beta-lactam resistance mechanism (moderate cephalosporinase hyperproduction, OXA-2 or PSE-1 enzyme production, non enzymatic resistance) and one strain was resistant to tobramycin (TOB). Antibiotic concentrations used for time-kill curves were 1/2, 1 and 2x MIC for cefpirome, 8 mg/l for tobramycin and 16 mg/l for amikacin (AKN). Bactericidal activity was defined as a (4 log10 reduction of the initial inoculum. At the concentrations used in this study, CPO was not bactericidal; AG were bactericidal in 3 to 24 hours. CPO-AG combination was bactericidal against all the strains with no secondary regrowth. For 7/8 strains, the combination of CPO with TOB and/or AKN was more rapidly bactericidal than the AG alone. In conclusion, despite an intermediate susceptibility against numerous strains of P. aeruginosa, the CPO-AG combination is bactericidal at concentrations achievable with standard dosing regimens in man.