A simple method for the determination of antibiotic sensitivity; an adaptation of the filter paper method.

The method to be described is based on the observation that the diffusion of the antibiotic from impregnated filter paper into the underlying medium is achieved in a very short time. Experiments were performed to show the influence on the size of the inhibition zone of the period of contact of the antibiotic strip with the medium. The results are shown in Fig. 1. Identical results were obtained with other antibiotics and with various organisms. It is therefore immaterial whether the filter paper remains in contact with the medium for a period longer than a certain minimum. It also does not affect the result whether the strip is left for the whole incubation period or removed before inoculation (Fig. 2). These results are in agreement with those obtained by Jensen and Kioer (1948) and M0rchLund (1949) who used wet antibiotic discs. Kokko (1947) and Evans (1948) made similar observations with regard to sulphonamides. These authors, however, regarded five hours as a suitable time of contact.