Bactericidal activity of meropenem against Pseudomonas aeruginosa

Ten strains of Pseudomonas aeruginosa that were susceptible to imipenem (MICs 2 mg/l) were exposed to a new parenteral carbapenem, meropenem (MIC 0.25 mg/l). Kinetic turbidometry showed that, as with other beta-lactam antibiotics, there was a prelytic increase in the culture OD following exposure to meropenem. The maximal value of the prelytic increase in the OD was higher for meropenem than for imipenem at concentrations 0.5, 1, 2, 4 and 8 x MIC. This corresponded to the formation of short filaments during exposure to low concentrations of meropenem. These filaments remained viable for 1-2 h, according to the drug concentration. For this reason, the killing began later with meropenem than with imipenem. After this delay, the killing rate for meropenem was the same as with imipenem, but occurred with lower concentrations of meropenem.