The gelatin film test for the demonstration of gelatin-liquefaction of bacterial cultures and stool suspensions is described. This test may aid in the identification of gelatin-liquefying bacteria, particularly members of the Pseudomonas and Proteus groups.

One hundred and seventy-nine strains of bacteria were tested. Positive results were obtained with Ps. aeruginosa, P. ammoniae and some strains of P. morgani. Negative results were obtained with 24 hour cultures of Staph. aureus hemolyticus and Esch. coli.

This test may be positive in dilutions of 24 hour broth cultures of gelatin-liquefying bacteria as high as 1:100,000 with an average of 1:200. The average number of such bacteria found necessary to give a positive gelatin film test is 960,000/2 drops of test solution (varying from 80,000 to 360 million). Bacteriologically sterile Seitz filtrates of gelatin-liquefying bacteria also gave positive gelatin film tests in high dilutions.

A mixture of gelatin-liquefying bacteria with saline suspensions of feces gave positive tests.

Stool cultures of four and duodenal cultures of three proved cases of cystic fibrosis of the pancreas revealed heavy growth of gelatin-liquefying bacteria. All these specimens gave positive gelatin film tests.

The presence of aureomycin in the stool (in concentrations of up to 1 mg./cc.) does not inactivate bacterial gelatinase.

The fact that bacteria present in the gastrointestinal tract may give a positive gelatin film liquefaction test makes mandatory the re-evalution of the positive feces "x-ray" tests for the diagnosis of cystic fibrosis of the pancreas. To avoid false positive gelatin film tests, the results of the test should be correlated with the presence or absence of gelatinliquefying bacteria.

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