Gram Negative Lab Report

INTRODUCTION
The Gram Negative lab had two parts; the aim of the first part is to determine the concentration of gram negative bacteria in a water sample collected from a creek near Providence Road, Strickling. Gram negative bacteria have a cytoplasmic membrane, a thin peptidoglycan layer, and an additional outer membrane composed of phospholipids and lipopolysaccharides. Because gram negative bacteria have a relatively thin cell wall when compared to gram positive organisms, they are consequently unable to retain the color of the crystal violet dye during gram staining (Barron, 1996). Two enumeration techniques were used during this part: Direct Count Procedure and Viable Count Spread Plate Procedure.
The aim of the second part of the experiment was to isolate enteric coliform bacteria from the water sample and determine its identity using biochemical testing. Enteric bacteria, members of the Enterobacteriaceae family, reside in the guts of animals, such as humans, and are usually harmless. Some of them, on the other hand, are pathogenic and are responsible for infections, food poisoning and plaque. Coliforms are bacteria that are always present in the
5 drops of methyl pH red indicator was then added. During the Triple Sugar Iron Agar (TSI) test, A TSI slant was inoculated with bacteria at 37oC for 48 hours. Color changes and production of gas were then checked for. For the Phenyl Alanine Deaminase test, a phenylalanine slant was inoculated and incubated at 37oC for 48 hours. 5 drops of 10% Ferric Chloride was then added, and was then checked for color change. The Decarboxylase Test was then conducted: Three test tubes of decarboxylase base, one containing no amino acid, and the other two had Lysine and Ornithine. Each test tube was inoculated with the bacteria and then overlaid with a thin layer of mineral oil. The tubes were then incubated at 37oC for 48