Studies on multiple-resistant Staphylococcus aureus. (I): Comparison of Antibiotic Sensitivity and β-Lactamase Producing Activity of Staphylococcus Aureus Isolated from Sputum in 1982 and 1985

The sensitivity to chemotherapeutic agents of the clinical isolates of Staphylococcus aureus were investigated in 1982 and 1985. In this investigation, a total of 18 chemotherapeutic agents were included: three penicillins, i. e., ampicillin, cloxacillin and piperacillin, six cephems, i. e., cefazolin, cefotiam, cefmetazole, ceftizoxime, cefoperazone and latamoxef, three aminoglycosides, i. e., gentamicin, dibekacin and amikacin, a tetracycline, i. e., minocycline, and others including rifampicin, vancomycin, nalidixic acid, norfloxacin and fusidic acid. In vitro antimicrobial activities of these agents against clinical isolates of S. aureus were determined immediately after isolation by the micro broth dilution method using the Dynatech MIC 2000 system. The activities of the above agents against 24 strains isolated from the sputum in 1982 were compared with those against 17 strains isolated in 1985. As a result, it was found that the recent clinical isolates of S. aureus were less sensitive to β-lactam antibiotics, other than latamoxef, than those isolated in 1982. In contrast, no difference was found in sensitivity of clinical isolates to non-β-lactam antibiotics, such as aminoglycosides, minocycline, rifampicin and nalidixic acid, between 1982 and 1985. The incidence of cefazoIin-resistant(MIC≿12. 5 μg/ml) strains of S. aureus increased from 12. 5%(3/24 in 1982) to 23.5%(4/17 in 1985). The incidence of cIoxacillin-resistant(MlC>12. 5 μg/ml) strains was 17. 6%(3/17) in 1985. The following agents such as cefmetazole, minocycline, rifampicin, vancomycin, norfloxacin and fusidic acid were found to be still very active against multiply resistant strains of S. aureus as compared with other agents examined. A recent increase in incidence of the strains of S. aureus which were highly productive of β-lacta-mase was evident as shown by the comparison of the data in 1982 with that in 1985. All of the strains producingβ-lactamase in abundance were found to be simultaneously resistant to aminoglycoside, minocycline, rifampicin and so forth. Thus, a very close correlation was suggested betweenβ-Iactamase producing activity and the mechanisms of resistance to non-β-Iactam antibiotics that are mentioned above.