A simplified plate method for detecting gelatine-liquefying bacteria.

Frazier (1926) described a plate method of testing for gelatine liquefaction. The gelatine was incorporated in a low-peptone agar medium. After growing the organism on the medium, the occurrence of digestion was shown by treating the plates with acid mercuric chloride or tannic acid. Frazier claimed that his method was more sensitive and gave quicker results than the usual gelatine " stab" method. Barer (1946) applied Frazier's method to freshly isolated bacteria from human material (chiefly intestinal Gram-negative bacilli) and found it satisfactory. Smith, Gordon, and Clark (1946) mention a simplification of Frazier's method which they used in examining aerobic sporing bacilli. Gelatine was incorporated in a concentration of 0.4% in nutrient agar instead of in a specially prepared basal medium. Evans and Wardlaw (1952) tried a similar method, incorporating 0.5% gelatine in non-nutrient agar, for measuring the gelatinase activity of B. subtilis culture filtrates, but found it unsuitable for accurate measurement. This paper reports an investigation of the simplified method (with a higher concentration of gelatine) which has been used in this laboratory for testing some bacteria of medical importance. The results have been compared with those of stab tests done at the same time.