Escherichia Coli

ANALYSIS OF A GRAM-NEGATIVE ENTERIC BACTERIUM

JOANNE VERNIE A. MENDOZA

INSTITUTE OF BIOLOGY, COLLEGE OF SCIENCE UNIVERSITY OF THE PHILIPPINES, DILIMAN, QUEZON CITY 1101, PHILIPPINES DATE SUBMITTED: 23 MARCH 2013 DATE PERFORMED: MARCH 5-14, 2013

ABSTRACT Enterobacteriaceae is a vast family of Gram-negative rods that naturally inhabit the gastrointestinal tracts of humans as well as animals. It is a heterogeneous group of bacteria that are able to ferment a wide range of carbohydrates, facultative anaerobes or aerobes, possess a complex antigenic structure, and produce a number of toxins and other virulence factors (Jawetz et al., 2012). Organisms under Enterobacteriaceae are identified and characterized through several qualitative tests that employ different types of growth media. In this unknown analysis, the identity of a certain enteric bacterium was established by examining and analyzing its growth on the different types of media that follow: Blood agar, MacConkey agar, Eosin Methylene Blue agar, Shigella-Salmonella agar, Triple Sugar Iron agar, Lysine Iron Agar, Simmons’ Citrate agar, and Sulfide-Indole-Motility medium. In addition, oxidase test was also performed. By virtue of the results obtained, the organism was determined to be Escherichia coli.

METHODOLOGY Day 1: Isolation of Pure Bacterial Colonies Using aseptic techniques, the sample was inoculated into a blood agar-MacConkey agar plate using steak plate method to qualitatively isolate discrete colonies of the bacterial sample. The medium with inoculum was subject to overnight incubation in an aerobic atmosphere at a temperature of 37˚C. The bacterial culture was then stored in the refrigerator until the second inoculation. Day 2: Preliminary Identification and Diagnosis of the Enteric Bacteria Isolated pure colonies were then inoculated aseptically into different types of previously prepared culture media employing the streak

plate method to provide qualitative data for the diagnosis of the...