Culturing Microorganisms from the Environment


Basic Techniques of Biotechnologies
  Cultivation of Microorganisms
    Culture Media
    Streaking Technique to Obtain Pure Cultures
    Pour-Plate and Subculture Techniques
    Culturing Microorganisms from the Environment

Microorganisms are found throughout the environment: in the air and water; on the surface of objects, clothes, tables, floors; in soil and dust; and on the skin and mucous membranes of our own bodies.

These widely present microorganisms ordinarily are of no concern to healthy humans, provided we maintain good hygiene in our daily living. In hospitals, however, where susceptible patients must be protected from hospital-acquired (nosocomial) infections, the concentration and distribution of microorganisms in the environment are of great importance. Frequent monitoring of the environment is one of the responsibilities of the hospital epidemiologist, who may be a microbiologist, nurse, or physician.

Purpose To take cultures from selected areas of the environment, in order to identify sources of
contaminating microorganisms
Materials Nutrient broth
Nutrient agar plates
Sterile swabs

  1. Place a swab in a nutrient broth to moisten it. As you withdraw the swab, press it against the inner wall of the tube to drain off excess fluid.
  2. Take a culture of the floor with this swab by rubbing and rotating it over an area approximately 10 cm square.
  3. Inoculate an agar plate with the swab by rotating it over a small area near one edge. Discard the swab and use your wire loop to streak out the plate in a manner to obtain isolated colonies.
  4. Moisten another swab in broth and take a culture of the sink faucet in the area around the aerator or strainer. Inoculate and streak another agar plate as in step 3.
  5. Take a fresh agar plate and touch separate areas of the agar surface with each fingertip of your right hand.
  6. Take an agar plate into the lavatory. Place it on a shelf or the basin, remove the top, and leave the agar exposed for 30 minutes. Close, invert, and incubate the plate at 35&degC.
  7. Look around the laboratory for any area where dust has accumulated (window ledges, open shelves, hard-to-clean areas). Take a culture of dust with a moist swab, inoculate, and streak an agar plate.
  8. Take a culture (with a moist swab) of a 5-cm square area on the front of your laboratory coat. Inoculate and streak a plate.
  9. Run a moist swab through your hair. Inoculate and streak a plate.
  10. Incubate all plates, inverted, at 35°C.