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BIOS242 Week 1 Lab 2 Techniques for Isolation of Pure Cultures-5.docx

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BIOS242 Lab 2Name:Lab 2: Techniques for Isolation of Pure CulturesLearning Objectives:Isolate pure cultures from a mixed population of microorganisms using aseptic technique.Learn the streak plate methodIntroduction:Microorganisms exist in nature as mixed populations of different species. In order to study them andobserve their characteristics it is first necessary to obtain pure cultures (a culture containing only onespecies of an organism).With millions of bacteria in a mixed sample, appropriate techniques must beused to reduce the numbers of organisms so pure colonies can be obtained.The streak plate method is most commonly used to isolate pure cultures.The sample/inoculum isdiluted by streaking it across the surface of an agar plate. While streaking in successive areas of theplate, the inoculum is diluted to the point where there is only one bacterial cell deposited every fewmillimeters on the surface of the agar plate. As these individual bacterial cells divide and produce newbacterial cells, an isolated cluster of cells, known as a colony, is formed. Since each colony comes fromthe growth and repeated multiplication of a single bacterium, all the bacteria present in an isolatedcolony belong to the same species.Therefore, each colony represents a large population of a singlespecies of bacteria. Pure cultures can be obtained by picking well isolated colonies and re-streakingthese on fresh agar plates.In this laboratory exercise, colonies from mixtures ofEscherichia coliandSerratia marcescenswill beisolated using the four-way streak method as summarized below (Figure 1).1Figure 1: Use the pattern on this figure to obtain single, isolated colonies.
BIOS242 Lab 2Name:We will need this image from Isolated colonies will be observed and described, using the information in figure 2 below.Figure 2: Characteristics of bacterial coloniesMaterials:A 24 hour nutrient broth mixture ofSerratia marsecens(S. marsecens) andEscherichia coli (E. coli), twonutrient agar plates per student, inoculating loops, incinerators/burnersNote to Students:1.You may use metal loops or disposable plastic loops. The instructions may vary based on thetype of loop. Please check with your instructor regarding usage and disposal of loops.2
BIOS242 Lab 2Name:2.You may use incinerator or burner with flame to sterilize metal loops. Please check with yourinstructor regarding how to safely use incinerators or burners to sterilize.

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Term
Summer
Professor
NoProfessor
Tags
Bacteria, Agar plate, Serratia marcescens, Isolation of Pure Cultures

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