OPTIMUM TEMPERATURE FOR DIFFERENTIATION OF ESCHERICHIA COLI FROM OTHER COLIFORM BACTERIA

During the past few years, several investigators have advocated the use of temperatures lower than 46TC. in the Eijkman test for Escherichia coli. Levine, Epstein and Vaughn (1934) sug-gested a temperature of 430 to 44TC. as optimum for selective growth of Escherichia coli in both the original Eijkman medium and in Standard Methods lactose broth. Their Aerobacter strains were markedly inhibited in both media at this temperature while some of the Citrobacter strains showed gas in the original Eijkman medium. None of the Citrobacter strains, however, produced gas at these temperatures in Standard Methods lactose broth of the A.P.H.A. Skinner and Brown (1934) criticized the Eijkman test because strains of Escherichia coli failed to grow in Eijkman's or Bulir's medium if the tubes were placed directly in a water-bath at 46TC. Wilson (1935), using the MacConkey medium, observed that practically all indol-positive strains of Escherichia coli grew well and produced gas from lactose at 440C. None of his strains of Aerobacter aerogenes produced gas at this temperature and very few grew at all. Minkevich, Alexandrov and Sobelova (1936) reported that a temperature of 460C. did not hinder their Escherichia coli cultures from fermenting mannitol in Bulir's medium if inoculated heavily, but in many cases, they contended, the high temperature of 460C. repressed growth of small numbers. Therefore, they proposed to make fermentation tests in Bulir's medium at 430 to 43.50C. Dodgson (1938) who has studied the application of the coliform index of pollution to shellfish for a number of years has conclude