Gelatin agar medium for detecting gelatinase production by anaerobic bacteria

A new medium, Lombard-Dowell gelatin agar, was developed for detecting gelatinase activity by anaerobic bacteria. The medium contained: Trypticase (BBL Microbiology Systems), 5.0 g; yeast extract (Difco Laboratories), 5 g; sodium chloride, 2.5 g; sodium sulfite, 0.1 g; L-tryptophan, 0.2 g; L-cystine, 0.4 g; hemin, 10.0 mg; vitamin K1, 10.0 mg; agar, 20.0 g; D-glucose, 1.0 g; gelatin, 4.0 g; and distilled water to 1 liter. The pH was adjusted to 7.5. The medium was dispensed in 100- by 15-mm quadrant plastic dishes (5 ml per quadrant). To test for gelatinase activity, we inoculated the medium with a young enriched thioglycolate or chopped meat glucose broth culture or a turbid cell suspension in Lombard-Dowell broth, using a sterile cotton swab, and incubated it under anaerobic conditions for 48 h at 35 degrees C. The quadrants were then flooded with Frazier solution, and clear zones around the bacterial growth were recorded as positive for gelatinase activity. The new medium was tested with a variety of anaerobic bacteria, and the results were compared with data obtained with the conventional technique for detecting gelatinase activity. Overall, there was satisfactory agreement between the two tests in the detection of gelatinase activity, but the Lombard-Dowell gelatin agar tests was more rapid and somewhat more sensitive than the conventional test.