Unknown Identification
Introduction to Microbiology Lab
Professor M
Biology Lab 1913 11/11/2014

I. Introduction
A series of tests was completed in order to identify an unknown microorganism. A gram stain reaction test was done. A gram stain reaction test is used to differentiate between two bacterial species. The two species; gram positive and gram negative bacteria have varying properties of their cell wall structural composition. The gram positive bacteria contain a thick peptidoglycan layer in their cell wall which retains the primary crystal violet stain. The crystal violet is washed from the fixed stain and gram-negative bacteria appear red after the decolorizer washes the primary stain due to their more porous higher lipid content walls and the safranin counter stain adheres to their thinner cell wall. The microscopic examination of the bacteria after staining allows for the morphology of the organism to be determined because as the cell is killed during the staining process it retains its rigid structure allowing for morphology determination.
A fermentation test was done. Three different carbohydrates are used to determine whether the organism can ferment a sugar as well as if a gas is produced during heterofermentation. A phenol red broth is used which retains a red color at a pH of 7.4 indicating no fermentation of a sugar. When an acid is produced during fermentation, the pH of the broth will lower and the broth will turn yellow. The sugars Glucose, Sucrose and Lactose along with the pH indicator were within the tested broths. Each tested broth had one sugar and an inverted glass vial called a Durham tube placed into the fermentation broth. This indicates if the organism could ferment and produce a gas in the tested sugars.
A cytochrome oxidase or simply oxidase test was completed. This test differentiates organisms that produce