A SIMPLE METHOD FOR THE CLASSIFICATION OF. BACTERIA AS TO
DIASTASE PRODUCTION. PAUL W. ALLEN. Dairy Bacteriology Laboratory,
University ...
A SIMPLE METHOD FOR THE CLASSIFICATION OF BACTERIA AS TO DIASTASE PRODUCTION
Received for Publication May 25, 1917
Among the various physiological reactions selected by the Classification Committee of the Society of American Bacteriologists for determining the identity of an organism the diastasic action presents the greatest difficulties. In all tests (seven are represented in the group number of the Society's classification card) of the activity of bacteria toward certain substances the aim is accuracy and ease of application. As at present carried out, the diastase test is far from satisfactory, not only because of the difficulty in obtaining potatoes of uniform quality, but also because of the difficulty arising when one tries to make a sharp distinction between "strong" and "feeble action." If the action is vigorous or if it is very feeble it is easily classed, but there are points between these extremes which produce doubt and the test then becomes a matter of mere judgment. During the last two years in the Dairy Bacteriology Laboratory of the University of Illinois the use of potato slants for the determinathion of diastase production by bacteria has been replaced by a simple plate method as follows: A starch agar is made by adding 0.2 per cent of water-soluble starch to the regular plain agar. This starch agar can be sterilized in the autoclave along with other media. Some hydrolysis takes place, but not enough to interfere with the test. The agar is poured into Petri dishes and allowed to cool, when a stroke 2 inches long is made with a loopful of an agar slant growth of the organism to be tested. The plates are incubated for two days at 37°C. and five days at 20°C., after which they are flooded with a saturated solution of iodine in 50 per cent alcohol. 15
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PAUL W. ALLEN Dairy Bacteriology Laboratory, University of Illinois
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PAUL W. ALLEN
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DIA8TATIC ACTION "STRONG,"" FEEBLE," AND "ABSENT"
SIMPLE METHOD FOR CLASSIFICATION OF BACTERIA
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A clear area about the stroke averaging more than 2 mm. in width classifies the diastatic action as strong, while a width of 2 mm. or less marks it as feeble an:d the absence of a halo as absent. These are the three terms used on the classification card of the Society of American Bacteriologists. As the loopful of growth from an agar slant is the unit amount of inoc4ulation which is used in all of the other tests which go to make up the group number of an organism, the starch agar test is consistent in this respect. As used in this laboratory, some of the evident advantages of this method over the potato slant method are the decrease in time and labor in the preparation of the media, and the greater *accuracy which the average worker can obtain. The starch agar gives best results if used before it is two weeks old, as after that period of time the starch becomes changed and spots of reddish purple develop on the addition of iodine solution. As to the comparison of this method with the potato test, it has been found that for the organisms of dairy products, approximately the same results are arrived at whether one test or the other is used.
