A study of antibiotic sensitivity testing with proposals for simple uniform methods.

The findings in the preceding paper on pages 773-778 are reviewed and the possible causes of error revealed by them are analysed. The disc test has been studied with a view to defining suitable culture media, and disc contents such that six can usually be placed on a 9 cm plate. Emphasis is placed on controlling the weight of the inoculum and on ensuring its uniform distribution. It is suggested that such cultures should be interpreted by comparison of inhibition zone sizes with those of a suitable control organism on the same medium. Indications and methods for tests in primary culture are discussed. Proposals are made for eliminating superfluous or inappropriate tests, thus limiting the number of antibiotics or other drugs with which tests need initially be done.