[Antimicrobial activities of ceftriaxone against clinically isolated strains]

Antibiotic activities (MICs) of ceftriaxone (CTRX) against 1,210 strains of bacteria including 28 spp. isolated in 1987 and 1990 were compared with those of other cephems. 1. When compared to data on clinically isolated strains reported in the early 1980s, strains of the following species isolated in 1990 showed extremely elevated MIC90s of CTRX: Staphylococcus spp., Streptococcus pneumoniae, Escherichia coli, Citrobacter spp., Enterobacter spp., Serratia spp., Proteus vulgaris, Morganella morganii and Providencia spp. No changes were observed in MIC90s between the 2 periods for microorganisms such as Streptococcus pyogenes, Haemophilus influenzae, Klebsiella pneumoniae, Proteus mirabilis and Peptostreptococcus spp. 2. The MIC90 of CTRX to S. pneumoniae was high because a large number of benzylpenicillin (PCG)-insensitive S. pneumoniae (PISP) was present among this species. The MIC80 to Bacteroides fragilis group was also high because highly resistant B. fragilis and B. thetaiotaomicron were isolated in large proportions among the bacteria of this group. Other oxime-type cephems also had high MICs against the above mentioned bacteria. Therefore, a further evaluation has to be made with regard to activities of oxime-type cephems such as CTRX against PISP and B. fragilis group. 3. Sample strains included, in high ratios, methicillin-resistant Staphylococcus aureus (MRSA), cephamycin-resistant as well as oxime-type cephem-resistant intestinal bacteria, Gram-negative bacteria, and new-quinolone-resistant bacteria. Some of there resistant bacteria are also CTRX-resistant, and CTRX had insufficient activities against them. 4. With regard to the assessment of changes of frequencies of specific drug-resistant bacteria, including those with CTRX-resistance from year to year, the authors would like to point out the following comment of theirs made in 1989 and 1991, which appears to be increasing its significance, "Subjects of future studies should include dose on the mechanisms for the acquisition of bacterial resistance to entire beta-lactam antibiotics and the social circumstances in which resistant bacteria appear". 5. It appears that those strains resistant to cephems including CTRX are increasingly found among clinically isolated strains in recent years. CTRX, however, was found still effective against most clinical pathogens. Furthermore, considering that CTRX is one of the few drugs which sustain high blood concentrations of active forms we concluded that CTRX is a useful cephem-group antibiotic.