Question

give a background and explanation for each of the following microbial tests

Oxidase test, TSI (KIA) test, The Enterotube II® System

Answer 1

oxidase test: it is used in microbiology to determine if a bacterium produces certain cytochrome c oxidases. it uses disks impregnated with a reagent such as N,N,N'N-tetramethyl-p-phenylenediamine (TMPD) or N,N-dimethyl-p-phenylenediamine (DMPD), which is also a redox indicator. the reagent is a dark blue to maroon color when it oxidized. and colorless when reduced. oxidase positive bacteria possess cytochrome oxidase or indophenol oxidase.(an iron containing hemoprotein). these both catalyse the transport of electrons. from donor compounds. (NADH) to electron acceptors. (Usually oxygen). The test reagent, TMPD dihydrochloride acts as an artificial electron donor for the enzyme oxidase, the oxidized reagent forms the colored compound indophenol blue. the cytochrome system is usually only present in aerobic organisms. that are capable of using oxygen as the terminal electron acceptor. the end product of this metabolism is either water or hydrogen peroxide.

TSI or KIA test: triple sugar iron agar is a differential medium that contains lactose, sucrose, a small amount of glucose, dextrose ferrous sulfate and the pH indicator phenol red. it is used to differentiate enterics based obn the ability to reduced sulfur and ferment carbohydrates. as with the phenol red fermentation broths, if an organism can ferment any of the three sugars present in the medium, the medium will turn yellow. if an organism can ferment dextrose, the small amount of dextrose in the medium is used by the organism within the first ten hours of incubation. after that time the reaction is produced. acid reverts in the aerobic area, of the slant and medium in those areas turn red., indicating the alkaline conditions. the anaerobic areas of the slants such as the butt , will not revert to an alkaline state, and they will remain yellow.