In the completed test of the multiple-tube fermentation method, a small portion of a coliform colony from the confirmed test that is positive is transferred to a growth medium and inoculated for _______, and a second portion is transferred to _______ and incubated for _______.

• A. 24-48 hr, LTB, 24-48 hr
• B. 18-24 hr, Brilliant Green Lactose (BGL), 24 hr
• C. 24 hr, BGL, 24-48 hr
• D. 18-24 hr, Lauryl Tryptose Broth (LTB), 24-48 hr

Answer: (D)

This item tests how the completed test in the multiple-tube fermentation method is performed to confirm a coliform from a positive confirmed test. After selecting a positive colony, you first place a portion into a growth medium and incubate it for about 18–24 hours to allow growth to develop. Then you transfer a second portion to Lauryl Tryptose Broth (LTB) and incubate for about 24–48 hours. Gas production in the LTB indicates lactose fermentation by a coliform, which helps confirm its presence.

The timing and media in this sequence are the key reasons this option is correct: the initial growth step (18–24 hours) prepares the organism, and the subsequent LTB step (24–48 hours) provides a reliable signal of lactose fermentation with gas production. The other choices mix incorrect timeframes or media that aren’t aligned with the standard completed-test procedure.