A New Medium for the Isolation of Corynebacterium Diphtheriae

Abstract

In the bacteriological diagnosis of diphtheria patients, the identification of the causative agent is so urgently required that it is usually not practical to examine its biological characteristicsthoroughly, and unlike in the bacteriological studies of other organisms, the morphological study has a great importance as well as in Mycobacteium tuberculosis.
In order to satisfy this clinical requirement, the factorsin blood agar medium whichaffect themorpholgy of Corynebacteriumdiphtheriae were investigated and the addition of beef heart extract was found to develop the typical forms of the organism. Various fractions from beef heart were then obtained by extracting it with ethanol and ether. In studying the effects of these fractions on the growth, morphology and appearance frequency of metachromatic bodies, it was found that the ether-insoluble fraction contained an effective factor common to gravis, intermedius and mitis, although itseffect on the morphology of intermedius was somewhat incomplete. Among various peptones tested, Tryptose (DIFCO) and S-peptone (EIKEN) were found to be satisfactory for the growth of Corynebacterium diphtheriae.
Furthermore, a new agar medium was prepared incorporating this ether-insoluble fraction, S-peptone, sodium fluorescein, and sodium arizarinate as used by Bregman for screening the suspicious colonies from their coloration. This medium was found to be as satisfactory as Loeffler's medium in regards to the morphology and appearance frequency of metachromatic bodies of the organism even in the initial isolation from patients. However, the rate of positive isolations from a large number of clinical specimens should be studied in the future. it is pointed out that this new medium is superior to Loeffler's medium in that the former gives a constant quality in every lot of preparation.