The MICs of
cefotiam and
cefazolin against K. pneumoniae DT-S were unaffected by the inoculum size and were 0.1 and 1.56 micrograms/ml, respectively. Bactericidal and bacteriolytic activities of the
cephalosporins were more potent in bacterial concentrations of 10(7) colony-forming units (CFU)/ml than in concentrations of 10(8) CFU/ml. Both activities of
cefotiam were more markedly influenced by bacterial concentrations than those of
cefazolin. Therapeutic activity of
cefotiam was about 9 approximately 15 times as potent as that of
cefazolin in experimental
pneumonia caused by K. pneumoniae DT-S in mice, and this finding was in accordance with the ratio of in vitro antibacterial activities of the two
cephalosporins as judged by the MICs or the bactericidal and bacteriolytic activities in bacterial
suspension of 10(7) CFU/ml. The range of concentrations of
cefotiam which induced cell filamentation in vitro, was wider than that of
cefazolin. This difference, however, was not reflected on the therapeutic activities of the two
cephalosporins in the model
infection. In the pneumonic lungs, definite therapeutic doses of both
cephalosporins (80 mg of
cefotiam per kg and 640 mg of
cefazolin per kg) produced mainly bacteriolysis of the challenge organisms.