Triple Sugar-Iron Agar The triple sugar-iron agar test or TSIA for short, is used to distinguish between the different types of Gram-negative bacilli, who can ferment glucose and produce a positive acid reaction. These bacteria are known as Enterobacteriaceae (Cappuccino and Sherman 2014f). This test tests for the presence of acid because of glucose fermentation, and the presence or lack thereof, of hydrogen sulfide. Like the carbohydrate fermentation test, the TSIA test medium contains lactose, sucrose and glucose to test for the presence of acid from the fermentation of carbohydrates. Phenol red acts as an indicator of this acid production by turning the slant from orange to yellow and sodium thiosulfate and ferrous sulfate act as a hydrogen …show more content…
The neck of the agar slant tube was flamed to ensure sterilization and the inoculation needle was stabbed straight down into the butt of the agar. The needle was then pulled straight upward, and the surface of the agar medium was streaked. One tube was inoculated for each of the two unknown substances. Both tubes were incubated at 37℃ for 24 hours and observed within 24 hours of incubation to avoid false results (Cappuccino and Sherman 2014f). A possible result of a red (alkaline) slant and yellow (acid) butt with or without the presence of the production of gas would indicate the fermentation of strictly glucose, due to the lower concentration of glucose than lactose or sucrose in the medium. A result of a yellow (acid) slant and butt with or without the presence of gas production would indicate that lactose and/or sucrose has been fermented, because of the higher concentrations in the medium providing more nutrients for the bacteria. A result of a red (alkaline) slant and butt would indicate the lack of any carbohydrate fermentation, meaning ammonia is being produced (Cappuccino and Sherman …show more content…
These microorganisms produce either catalase or superoxide dismutase to degrade hydrogen peroxide, which is toxic to the bacterial cells (Cappuccino and Sherman 2014g). The production of catalase in an organism can be determined by adding hydrogen peroxide to the bacterial sample and identifying the presence of oxygen gas in the form of bubbles. The absence of bubbles after adding hydrogen peroxide to the bacterial sample indicates a negative result and indicates that the organism does not produce the enzyme catalase (Cappuccino and Sherman 2014g). The catalase test is a simple test, performed by placing a sample of the organism on a glass slide. A small amount of the microorganism was obtained using a sterile inoculating loop and proper aseptic technique. This was then transferred to the appropriate glass slide and the loop re-sterilized. One drop of 3% hydrogen peroxide was then added to the sample on the glass slide and observed for the presence or lack of bubble formation (Cappuccino and Sherman