A SYSTEM FOR THE BACTERIOLOGICAL EXAMINATION OF WATER

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Abstract
Comparative tests using Bacillus coli, B. aerogenes, B. subtilis, Staphylococcus aureus, and Staph. albus showed the superiority of crystal violet over brilliant green as a bacteriostatic agent. A crystal-violet broth medium for the presumptive test is described: peptone (Difco), 15 gm.; K2HPO4, 15 gm.; KH2P04, 3 gm.; lactose, 15 gm.; crystal violet (1:5000 solution), 21.5 cc; distilled water, to make 2000 cc. Production of acid and gas in this medium in practically 100% of the samples examined is due to members of the coli-aerogenes group. An agar-dye differential medium is described: peptone (Difco), 10 gm.; K2HPO4, 3 gm.; KH2PO4, 0.6 gm.; lactose, 5 gm.; agar, 20 gm.; distilled water, 1000 cc; erythrosine (2% aqueous), 20 cc; methylene blue (1% aqueous), 20 cc; brom cresol purple (1% alcoholic), 2 cc. Results on this medium are equivalent to a partially confirmed and a confirmed test, i.e., 2 tests are obtained in 1 operation. B. coli and B. aerogenes are sharply differentiated because of distinct differences in carbohydrate metabolism. Results of water examinations are detailed, showing the superiority of the method over that given in "Standard Methods." The method not only gives more clear-cut results, due to elimination of interfering non-colon organisms, but also a saving of at least 24 hrs. in time for complete analysis.