LifeLines OnLine
2002 Summer Faculty Workshop
The Case: And what's hiding in your sponge?

Part 1.  

Jane had a long series of irritating skin rashes.  She had been to several doctors, but none of them came up with a diagnosis -- all the samples they sent to the lab came back as negative for pathogenic bacteria.  Finally, one nurse suggested she bring in her shower sponge and washcloth.  When the loofa sponge was squeezed, a green slime, the same color as her shower gel, came out.  Samples of the sponge and wash cloth were sent to the lab for culture.  The lab routinely uses enriched media, to be sure to find all organisms present.

Part 2.

Results from the lab:
Sample 1 (wash cloth):  no growth after 48 hours
Sample 2 (loofa sponge):
  Pseudomonas aeruginosa

Explain these results.

Case Author: Julie Harless
Montgomery College,

Case Analysis

Possible issues:
Nutritional requirements of bacteria.
Physical conditions for bacterial growth.
Opportunistic infections.
Methods of sanitation.

Option: Include a know / need to know chart like the one below:

What do you know?
What do you need to know?

Learning Goals

  • Identifiy basic growth requirements for bacteria
  • Understand that different organisms have different nutritional requirements
  • Be able to distinguish between minimal and enriched medium
  • Have experience with experimental design
  • Practice collaboration skills
  • Gain confidence in applying information to a new situation.


Investigations and Activities

Laboratory exercises:

1. Directed type of laboratory:  students test different standard media for their ability to support growth of different bacteria (Pseudomonas, Staphylococcus, E. coli).  Results of this exercise can then be used as background information and a starting place for group experiment.

2.  In groups, students will be asked to design a growth medium that will support growth of Pseudomonas aeruginosa, but will not allow E. coli growth.


Text book

General information web sites:

Medical Microbiology

Web sites of Microbiology courses:

Lab Manual Appendix, media recipes

Difco Manual, media recipes

Modeling software for microbial growth simulations:


Download this handout (editable Word document)

Directions for one page analysis

Lab protocol for standard media tests

Analysis chart for selective media experiment.

Student Products

Group:  List of issues to be investigated.

Individuals:  Short (one page) analysis of case.
Entries in lab notebook of results and interpretation of standard media tests.

Group:  Outline of experiment to design a selective medium.  
Report with background, experimental results, and conclusions.
Recommendations for types of sponges that will not support microbial growth.

Assessment and Evaluation Plan

5%  Initial analysis of case in group discussion.  List should include some of the topics in learning goals. (Grade in class, give feedback before they start writing individual analyses.) 

25%  One page individual analysis of case.  Looking for understanding of the different growth conditions in a sponge and a cloth, the basic requirements for living organisms.

20%  Flow chart for standard media assay, results and interpretation of results.

20%  Design of experiment for selective medium
           a.  components that are necessary for all organisms
           b.  which components will be varied, which constant

30%  Results of experiment:  group lab report with background, results and conclusions.  Report form included with explicit outline of nutritional requirements.
Recommendation of types of sponges that will not support bacterial growth.

Terminology and application questions included on exam.


Identify the specifics for using the cases in your classes.

Course name:
Likely sequence in syllabus:
Time during term:
 Week 3-4 in the semester
 1.5 weeks
 Classroom discussion, laboratory
Students in course:
 Sophomore, allied health, some biology majors
Collaborative elements:
 Group discussions in class to define the  problem, identify resources. Groups in lab to  perform first experiment, design and perform  second experiment, written group report for  experiment 2.



Photographs:  Neal Chamberlain, Kenneth Todar, Bernard A. Cohen, Chrisoph U. Lehmann

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