Urea is a metabolic product that is give off as waste. Since it is toxic to most organisms, microbes that are susceptible to urea's harmful effects have a line of defense known as urease. Urease is an enzyme that catalyzes the decomposition of urea into the products carbon dioxide and ammonia. Once an unknown bacterium is isolated and diluted in liquified agar, urease production in the bacterium can be tested. Using aseptic technique, a loop of bacteria is transfered to a tube of urea broth containing phenol red, a common pH indicator. After an incubation of 48 hours, the urea broth is examined for a color change. If the bacteria form urease, the medium will have changed colors from yellow to hot pink because the released ammonia raises the pH above 8.1, the critical color change value for phenol red.