Biochemical Test Lab Report

Introduction: The purpose of this lab is to use staining techniques and biochemical testing to identify an unknown bacteria using Bergey’s manual. Bergey’s manual of Systematic Bacteriology is a dichotomous key primarily used to identify a bacterial species. Biochemical tests are used to differentiate different species of bacteria. These tests are effective in determining the characteristics of the microbe being tested. Such characteristics include citrate utilization, gelatin hydrolysis, nitrate reduction, etc. Biochemical testing is very important in the medical field when a patient is infected with an unknown microbe. Such testing can identify the microbe(s) and types of medications effective in treating the infection. It is also useful
The bacteria must posses of the membrane-associated transporter citrate permease to utilize citrate. The byproduct of citrate utilization is alkaline. A positive test results in a color change of the medium from green to blue. Materials needed include simmons citrate agar slant tube, and a pure culture of bacteria. The starch hydrolysis test is used to determine the ability to hydrolyze starch. Bacteria use amylase, an extracellular enzyme to hydrolyze bonds linking the glucose subunits. Starch is detected by adding iodine to the medium. If the bacteria growing on the starch agar produce amylase, no color change will be seen around the bacterial growth because all of the starch is consumed. The absence of a color change is a positive test. Materials needed to perform this test include a starch agar plate, Gram’s iodine, and a pure culture of bacteria. The casein hydrolysis test determines the ability of bacteria to hydrolyze casein. Casein is the predominant protein in milk and can be used as a substrate to assess the production of proteinases. If bacteria secrete caseinase, a specific protease, casein molecules are digested in the area around the bacterial growth is clear. A clear zone is a positive test. Materials needed include a skim milk agar plate, and a pure culture of bacteria. The Gelatin hydrolysis test determines whether a bacteria is able to hydrolyze gelatin or
Some bacteria use the enzyme urease to degrade urea into carbon dioxide and ammonia. The appearance of bright pink is a positive test for a urease-producing bacteria. Materials include a urea-containing medium, and a pure culture of bacteria. The litmus milk reactions are used to determin whether bacteria have the ability to utilize lactose, protein, and litmus or not. The litmus serves as a pH indicator which turns pink in the presence of acid and blue in alkaline. If sufficient acid is produced, casein will be denatured and form a firm curd and whey which is a clear, watery fluid at the top of the curd. Some bacteria that form this acid curd will reduce litmus to a colorless compound and appear white, which begins at the bottom of the tube. A soft curd can form when casein is altered by the enzyme renin and the color of the litmus does not change. Medium that is clear results from prteolytic bacteria that completely digest the curd or insoluble casein. Materials needed include a litmus milk tube and a pure culture of