One hundred strains of Klebsiella pneumoniae, resistant to amikacin and ceftazidime, were tested in vitro for susceptibility to meropenem, imipenem, cefepime and cefoxitin by the E test, and tested for susceptibility to ciprofloxacin by the disk test. All strains tested were highly susceptible to meropenem and imipenem with minimal inhibitory concentrations for 90 percent of the strains (MIC90) of 0.125 and 1 mg/L, respectively. Seventy-seven and 61 percent of strains were susceptible to cefepime and cefoxitin, but with lower levels of activity with MIC90 of 64 and > 256 mg/L, respectively. Only 32 percent of strains were susceptible to ciprofloxacin. All 13 strains resistant to amikacin, ceftazidime, cefepime, cefoxitin and ciprofloxacin were susceptible to meropenem and imipenem.
These results suggest that meropenem and imipenem should be recommended as therapy for multiresistant K. pneumoniae infections. Other antimicrobial agents might be useful but should be confirmed with the antimicrobial susceptibility test. Cefoxitin should be used with special caution because of its very high MIC90 .