An Unidentified Growth Factor for Certain Strains of the Diphtheria Bacillus

Abstract

It has been possible to grow a number of strains of the Park 8 variety of diphtheria bacillus, as well as one or 2 other unrelated strains, on media of entirely known composition. 1 Growth obtained on such media is extremely luxuriant, yet a number of the factors essential for the growth of organisms such as the staphylococci, the streptococci and the pneumococci are absent. It appeared, therefore, that such a medium might be unusually suitable for diagnostic purposes in preparing media for throat cultures to replace the ordinarily used Loeffler medium. A medium based upon Formula A in the paper referred to above has therefore been prepared, solidified by the addition of 2% agar, and used for the cultivation of organisms obtained by throat swab from a considerable number of individuals, both normal and suffering from clinical diphtheria.

The results in general, although encouraging, have been too unsatisfactory to suggest any immediate practical value for the method. The majority of normal throats yield no growth whatever after 24 hours' incubation. A certain number of cases of diphtheria, or cultures taken from the throats of individuals known to harbor the diphtheria bacilli, have given strongly positive growth of practically a pure culture of diphtheria. On the other hand, there are a certain number of normal throats which contain organisms capable of growth on this medium, a matter naturally to be expected, but there are also a number of cultures known to have been taken from positive throats which yielded no growth.

In following up this matter, it appeared that the difficulty lay in the fact that even with strains which grow well on the simple medium, a light inoculum generally fails to grow.