Abstract
The sugar fermentation test is an important criteria in identification of lactic acid bacteria. Usually, the sugar fermentation is detected by acidformation from a sugar given in growth media. In the ordinary method, acid-formation is indicated by the value of titration of the media by alkali-solution or by the color-change dye (i.e. bromcresol purple) previously added to the media.
In the present paper, we described a new method using an agar-plate in the sugar fermentation test. An agar-plate containing one sugar as the sole carbon source, yeast extract, peptone, inorganic salts and CaCO3 as the acid indicator was prepared in a 90mm diameter petridish. The agarplate was covered with sterile 1.5% agar. Test strains of lactic acid bacteria were inoculated on the agar-plate by stabbing.
The sugar fermentation reaction was easily detected by observing the incubated agar-plates. In positive reaction, a clear zone of dissolved CaCO3 by the acid produced was observed around the stab line on the agar-plate; whereas in negative reaction, the clear zone was not observed. A maximum of 20 lactic acid bacteria strains can be tested on an agar-plate prepared in a 90mm petridish.
