Abstract
The performance of Rapid Media-DO (RM-DO, Morinaga Milk Industry Co., Ltd.), a culture medium for rapid testing of coliforms, was experimentally examined.
RM-DO is a prepared culture medium poured and solidified in Petri dishes in advance of testing. After a test sample is inoculated on the medium, allowed to absorb into it, and incubated, colonies that form on the surface of the medium are counted.
RM-DO is prepared by dissolving powdered ingredients as in desoxycholate agar medium but with a greater amount of water than usual, and adjusting the water content by drying it to the prescribed level. As a result, RM-DO is able to absorb much more test sample than a conventionally-prepared plate (0.1-0.2ml), and it absorbed 1ml of a test sample within 30 minutes.
The growth of coliforms was rapid in RM-DO, because bacteria grew on its surface, and there was no effect of heat from the poured medium, so that the incubation period could be shortened to 12 hours compared with that by the desoxycholate pour plate method (20±2 hours). In addition, the confirmatory test for coliforms could be performed simply and rapidly by directly dripping X-GAL/dimethylformamide solution over the colonies on the surface of the medium.
In a comparative study with other media using milk inoculated with coliforms as well as raw milk, both bacterial counts and detection rate in RM-DO were comparable or superior to those by the desoxycholate agar pour plate method.
