In vitro activity of moxalactam and cefoperazone against Streptococcus pneumoniae with differing susceptibilities to...

In vitro studies were performed to examine the potential usefulness of two new drugs, moxalactam and cefoperazone, for the treatment of infections caused by Streptococcus pneumoniae. 34 isolates of S. pneumoniae with differing susceptibilities to penicillin were examined by disk diffusion, agar and microbroth dilution methods. Isolates highly resistant to penicillin (MIC greater then 1 microgram/ml) were also resistant to moxalactam (MIC = 128 micrograms/ml) but were sensitive to cefoperazone (MIC = 2--4 micrograms/ml). All isolates relatively resistant to penicillin (MIC 0.25--0.5 micrograms/ml) were sensitive to cefoperazone (MIC 0.25--1 microgram/ml) and had moxalactam MICs of 4--16 micrograms/ml for 10/12 isolates. The disk diffusion test was unreliable for detecting strain relatively resistant to moxalactam. These studies showed that cefoperazone is more active than moxalactam in vitro against S. pneumoniae regardless of the penicillin susceptibility of these bacteria.