Enrichment and Identification of Enterobacteriaceae

Enrichment and Identification of Enterobacteriaceae -...

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Enrichment and Identification of Enterobacteriaceae By: Alex Katler Lab Partner: Erica Wagner Lab Section 2 Experiment 9 Report
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Introduction: Enterobacteriaceae , also known as enterics, are probably the best characterized family of prokaryotes. This is because every human on the planet is affected by their presence in the normal flora of our intestinal tracts. Some enterics are helpful in the development of local and systemic immune response in infants. 1 At the same time, some pathogenic enteric microbes have been responsible for the worst disease pandemics in the history of the world. This family can generally be characterized as Gram negative, non-sporulating, short rods that are either non-motile or have peritrichous flagella. 2 Also, they are facultative anaerobes that can be fermentative and have simple nutritional requirements. 2 As a group, they are very similar to each other sharing many physiological processes. A key difference between members of this phylogenic family is the method by which they ferment glucose. Anaerobically, “mixed acid fermenters” metabolize glucose to various types of acid (including lactic acid), ethanol and carbon dioxide and hydrogen gas which usually lowers growth medium to around pH 4.4. “Butanediol fermenters” have the same metabolic products as the mixed acid fermenters except they also produce a detectible chemical called butanediol. 2 Today, a specific group of enteric microbes called coliforms have been utilized in a very important way. These microbes can help in the identification of water contamination. Many diseases are spread through fecal contamination of a water supply by infected individuals. 2 Since coliforms are commonly found in human and animal feces, if they are found in a water sample it would be a good indicator that the source where that water sample came from had fecal contamination. 2 These coliforms are termed indicator organisms and are generally not harmful themselves. One of their distinguishing traits seperating them from general enterics is that they ferment lactose to acid and gas within 48 hours. 2 If they are detected then more expensive tests can be done to possibly identify more pathogenic organisms. The main point about coliforms as indicator organisms is that if they are present in water, diseases might be present too. To isolate coliforms or any type of Enterobacteriaceae from a sample containing few desired organisms and/or other organisms, a selective enrichment must be performed allowing growth of the desired microbes while inhibiting any others. An incredible variety of media exist for this purpose. After enrichment and isolation of a 2
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general enteric or coliform, many types of test media and reagents can be used to characterize the microbes more specifically.
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This note was uploaded on 05/09/2008 for the course BACT 303 taught by Professor Forrest during the Spring '08 term at Wisconsin.

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Enrichment and Identification of Enterobacteriaceae -...

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