List of experiments  



Environmental Microbiology
Experiments for middle and high school

Christine L. Case
Skyline College


Laboratory Safety   All of these labs can be done with minimum safety precautions. Laboratory safety is described below.

General Guidelines
Standard Practices for the Student
Standard Practices for the Instructor
Laboratory Facility




Used materials can be collected in 5% household bleach for disposal. Your local college, hospital lab, public health lab, water treatment plant lab or wastewater facility lab might provide "red bags" for discarded materials. The full bags could be returned to them for sterilization and disposal.



The cultures will grow fastest at the temperature indicated in the protocol, however, all of the cultures will grow at room temperature. When room temperature is used, the cultures will grow slower so observation periods should be timed accordingly.


Bacterial cultures

These experiments use natural bacterial populations, however it is always prudent to handle any bacterial culture following standard safety precautions.








General guidelines

1. No eating or drinking during lab.

2. Wash the desktops with a disinfectant before an experiment. Lysol or 5% household bleach will work. This is to reduce contamination of the experiment.

3. All used materials, e.g., swabs and Petri plates containing culture media, should be collected in a "red bag" or in a container of 5% household bleach for disposal.

4. Keep your fingers out of bacterial cultures.

5. If a bacterial culture is spilled, cover the spill and glassware with paper towels and soak with disinfectant. After 20 min., clean up the mess being careful not to touch broken glass.

6. Wash the desktops with disinfectant after each experiment.

7. Wash your hands after working in lab.

Standard Practices for the Student  


  1. Work surfaces are disinfected at the beginning and end of every lab period and after any spill. Appropriate disinfectants include: 1:10 dilution of household bleach (hypochlorite), phenolics, and glutaraldehyde.*
  2. Mechanical pipetting devices are used; mouth pipetting is prohibited.
  3. Eating, drinking, smoking, storing food, and applying cosmetics are not permitted in the laboratory.
  4. Wash your hands after every laboratory exercise. Bar soaps may become contaminated, therefore, liquid or powdered soaps should be used.
  5. Broken glassware and other sharp objects are put in the appropriate container. Broken mercury thermometers are handled separately. Red alcohol thermometers can be substituted for mercury thermometers.
  6. Glassware and slides contaminated with microorganisms, blood, urine, and other body fluids are placed in disinfectant. They can be washed after disinfection.
  7. Hands should be washed immediately and thoroughly if contaminated with blood or other body fluids.
  8. Work only with your own saliva, blood, urine, tears, and other secretions and excretions.
  9. Don't do unauthorized experiments.
  10. Don't use equipment without instruction.
  11. Horseplay will not be tolerated in the laboratory.

*California Health and Welfare Agency, Infectious Disease Branch. California Morbidity, #37, September 23, 1988.

Standard Practices for the Instructor  
  1. Laboratory doors are kept closed when experiments are in progress.
  2. The instructor controls access to the laboratory and limits access only to persons whose presence is required for program or support purposes.
  3. Contaminated materials that are to be decontaminated at a site away from the laboratory are placed in a durable, leakproof container that is closed before being removed from the laboratory.
  4. An insect and rodent control program is in effect.
  5. A needle should not be bent, replaced in the sheath, or removed from the syringe following use. The needle and syringe should be promptly placed in a puncture­resistant container and decontaminated, preferably by autoclaving, before being discarded or reused.
  6. The instructor should be informed by students who become pregnant, are taking immunosuppressive drugs, or have any other medical condition (e.g., diabetes, immunologic defect) which might necessitate special precautions in the laboratory.

Laboratory Facility  
  1. Interior surfaces of walls, floors, and ceiling are water resistant so that they can be easily cleaned.
  2. Bench tops are impervious to water and resistant to acids, alkalis, organic solvents, and moderate heat.
  3. Windows in the laboratory are closed and sealed.
  4. An eye wash is present in every laboratory.


Any powdered or liquid soaps may be used for routine handwashing in the laboratory. Bar soaps should not be used since they can become contaminated. Liquid soaps which do not contain a preservative should be cleaned out routinely and replaced with new soap. Powdered soaps have the advantage of not becoming contaminated or allowing organisms to grow in them.

Rapid disinfection of hands may be accomplished by the:

  1. Use of wescodyne­detergent preparation and scrub for 30 to 60 sec. Rinse with water.
  2. Use of 4% chlorhexidine­detergent and scrub for 30 to 60 seconds. Rinse with water.
  3. Use of a phenolic disinfectant­detergent for 20 to 30 sec and then rinse with water.
  4. Use of alcohol (50­70%) for 20 to 30 sec, followed by a soap scrub of 10 to 15 sec and rinse with water.

Spills of microbiologic material onto bench tops may be disinfected by using a disinfectant­detergent according to the manufacturers directions. If a hypochlorite solution (household bleach) is used, remember that it is easily neutralized by organic matter, may discolor surfaces, is corrosive to metals, and has an unpleasant odor.

Potentially infectious wastes including human body secretions and fluids and objects, such as slides, syringes, lancets, and bandages, contaminated with these materials should be placed in labeled containers container. Note that "sharps" (including broken glass) must be placed in a puncture­proof container. Contaminated glassware should be placed in a container of disinfectant.

Contaminated glassware should be decontaminated before washing. Decontamination can be by:

1. Autoclave or pressure cooker at 121°C at 15 psi for 15 min.

2. Soaking in 10% household bleach for 30 minutes.

Contaminated disposables such as bandages and plasticware should be "red bagged" and autoclaved (at a local hospital or college). Your local scavenger may have a procedure they use for physicians, dentists, and your school health center.

Keep squirt bottles of disinfectant on hand to cover spills and wash work surfaces:

Standard laboratory disinfectants Examples
Halogens Household chlorine bleach, 1:10
Alcohols 70% Ethyl alcohol
Phenolics Amphyl®
Aldehydes Glutaraldehyde, 1%
Quats Sanisol®