Biochemical tests used for identification of Escherichia coli from other coliforms

Glucose Fermentation: The tube is red originally from the phenol red acid/base indicator. If the organism ferments glucose, acids are produced and the tube turns yellow. An inverted tube traps gas and shows that gas is produced as well as acids. All coliforms produce acid and gas on both glucose and the lactose  fermentation tube (second tube). The third tube is the citrate test. If the organism uses citrate, it grows. If it doesn't use it, it doesn't grow. E. coli is negative, but Citrobacter, Klebsiella, and Enterobacter are all +.
The 4th tube is the SIM test - 3 tests in one tube - The most important one here is the indole test. If the organism produces indole, it can be detected by adding Kovac's reagent, which turns red in the presence of indole. E. coli is positive, the others are negative. The phenylalanine test is the 5th tube. If the organism breaks down phenylalanine, then a compound is formed which turns green when you add ferric chloride solution. All of the coliforms are negative for this, but one of the non-coliform fecal bacteria - Proteus - is +.  The swab is for the oxidase test. All the coliforms are oxidase neg.
Since E. coli is the only coliform that is found only in feces, and is not naturally environmental, as the other coliforms occasionally are, it is important to check to see if E. coli is found in the testing site (Four Pole Creek) as well as the other coliforms.  This pic is from a colony from the preliminary testing site below the tennis court area. It proves that E. coli is there. Alex inoculated 4 colonies from a plate into sets of biochemical tests the same as in the picture. This pic shows E. coli, and the other 3 were indole +, showing that E. coli was in those colonies, but it appeared to be mixed with other coliforms, since the citrate was positive in all of the others.  All 4 of these tubes were inoculated by Alex.