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Appl Environ Microbiol. 1970 September; 20(3): 447-451
Copyright © 1970 American Society for Microbiology. All Rights Reserved.

Stability of Antibiotics and Chemotherapeutics in Agar Plates

Clinical Microbiology Laboratories, University Hospital, and Department of Microbiology, University of Washington School of Medicine, Seattle, Washington 98105
Mayo Graduate School of Medicine, Rochester, Minnesota 55901

ABSTRACT

The stability of chemotherapeutic agents incorporated into agar plates was studied by comparison of minimum inhibitory concentrations on fresh and stored plates and by direct bioassay of the chemotherapeutic agar plates. Plates were stored in sealed bags at 4 C. No loss of bioactivity was demonstrated after 30 days of storage in plates containing methicillin, erythromycin, cephalothin, tetracycline, chloramphenicol, kanamycin, streptomycin, polymyxin B, or nalidixic acid. Penicillin G, ampicillin, and nitrofurantoin showed statistically significant losses of activity after 4 weeks. None of the chemotherapeutics tested showed significant loss in activity after 1 week.