On the suitability of gelatin for plate cultures. I.

Summary

It was found that the dimesions and the shape of bacterial colonies formed on nutrient gelatin are highly dependent on the brand of gelatin used. Out of twenty one samples from different sources only two proved to be satisfactory from this point of view. The remaining nineteen only yielded pin-point colonies in counting plates of various water samples.

The most striking difference between the two types of gelatin was manifested in the appearance of surface colonies ofBacterium coli and ofFlavobacterium aquatile. On the gels made from the gelatin of poor quality the colonies were small, circular with sharp edges, whilst the gelatin of good quality gave rise to colonies of much larger size which spreaded over the surface, with irregular, often lobated circumferences (“Weinblattform” ofB. coli).

An attempt to find a correlation between this behaviour of the gelatins and some of their chemical and physical properties was unsuccessful. Neither the organic sulphur content, nor the viscosity, the hardness, or the iso-electrical point of the gelatin proved to be responsible for the established difference.

A continuation of this study which led to some insight into the problem will be dealt with in the following communication (Rook andBruckman, 1953).