Microbiology 102:
A General Review of Enrichment and Isolation Experiments

This page covers the four parts of Experiment 11 and
will be passed out as a handout in lab (Period 8)


I.  REVIEW OF THE GENERAL PROCEDURE FOR THE ENRICHMENT, ISOLATION AND IDENTIFICATION OF BACTERIA as outlined in the lab manual:

ENRICHMENT AND ISOLATION PURE CULTURE WORK
SOURCE
MATERIAL
BROTH
ENRICHMENT
PLATING FOR
ISOLATION
STOCK
CULTURES
CHARACTERIZATION & IDENTIFICATION
•Consider inoculum: what organisms may or may not be present.
•May pre-treat inoculum, e.g., by heat-shocking.
•Usually is selective.
•May be skipped altogether.
•Usually selective or selective-differential – but not always!!  
Throughout procedure, appropriate media and incubation conditions must be considered.

II.  A "WORKSHEET" TO HELP US ORGANIZE AND SUMMARIZE THE SPECIFIC FACTORS that allow isolation of the various types of microorganisms in these experiments:

  11A
Streptomyces
11B
Purple "non-sulfur" photosynthetic bacteria
11C
Bacillus
11D
N2-fixing bacteria
Special properties of desired organism that can be exploited to help us "sort it out" from others.
Likely source material (habitat of organism or where the organism is a significant contaminant).  
 
     
Treat sample to enhance isolation?        
Need to use enrichment?        
Factors to consider for the enrichment & plating media:*
•Selective by restriction of nutrients or addition of selective agents?
•Special sources of C, N, energy?
 
 
 
 
(Why is 2nd plating medium an all-purpose medium?)
**    
Special incubation conditions?   **  
 
 
 
Detectable features of the desired organism that help us in picking and identifying it.   **    
Any special, additional tests on the isolates? (That is, tests not essential to identification to the genus level.)  
 
 
     

  *  For the desired type of organism, the medium/media must include the required elements (including trace elements) and whatever growth factors are needed. Note that these organisms are all heterotrophs and organotrophs. (A review of Appendix D in the manual is useful.)

**  See question 11B in the compilation of old quiz questions. How would we want to grow the purple non-sulfur photosynthetic bacteria to maximize their detection and minimize growth of other organisms – as phototrophs or as chemotrophs?


Go to our
Old Enrichment and
Isolation Page
.
Page last modified on 10/22/10 at 8:00 PM, CDT.
John Lindquist, Department of Bacteriology,
University of Wisconsin – Madison