Antibiotic Sensitivity Discs

KRAMER, JULIAN (Food and Drug Administration, Washington, D. C.), AND AMIEL KIRSHBAUM. Effect of paper on the performance assay in the control of antibiotic sensitivity discs. Appl. Microbiol. 9:334-336. 1961.-Antibiotic discs were prepared, using several several batches of papers meeting Food and Drug Administration specifications. The analysis of 1,152 zones of inhibition produced showed no performance differences among these batches. Other discs were prepared using papers of different grades. These produced large differences in performance. It is obvious, therefore, that the use of a specified disc paper is necessary for standardizing the performances of the products of various manufacturers and that reproducible results can be attained with the grade of paper specified. The characteristics of the paper used are an important consideration in the manufacture of sensitivity discs. Because of the use of paper as matrix in this product, these characteristics rank highly as potential sources of variation in the performance of discs. The various manufacturers have selected papers suitable to the requirements for their final products. The specifications of these papers vary somewhat as to weight, thickness, anid absorbability of water. For this very reason, paper must play a major role in the standardization of discs. The proposed regulations of the Food and Drug Administration (FDA) for the assay of discs (Anonymous, 1960) specify the paper to be used for the preparation of the control discs. This present work was undertaken to answer questions raised about the reproducibility of results that can be obtained with different commercial batches of paper of the specified grade. In this publication "different batches" refer to paper of the same specifications but manufactured at different times, whereas "different grades" refer to papers with different specifications. The Food and Drug Administration specifies that the blank discs used in the control of commercial discs "be 14 inch in diameter, of paper weighing approximately 30 mg per square centimeter that will absorb approximately 3 times its weight of distilled water." Ostrander and Griffith (1959) used an exquisitely sensitive indicator organism in a study of the effects of 16 different papers used to make penicillin discs. With this sensitive organism, two units of penicillin is in the upper range of concentrations where further increases of concentration produce no further response. This study indicated that unless some other agents, such as certain dyes, were present, the paper used made no difference in the performance of the disc. In our study the organisms used were those designated in the FDA proposed regulations.' Each of these organisms was originally selected because its sensitivity is such that an essentially linear response is obtained to the concentrations of antibiotics used. The study was made in two parts so that these questions might be answered: (i) Is there any difference in performance among discs made with different commercial batches of paper meeting Food and Drug specifications, and (ii) are there performance differences among discs made with papers that do not meet these specifications? I The organism used for polymyxin was Bordetella bronchiseptica. ::334 [VOL. 9 on O cber 5, 2017 by gest ht://aem .sm .rg/ D ow nladed fom ANTIBIOTIC SENSITIVITY DISCS METHODS AND MATERIALS