Culturing a Fecal Sample


Diagnostic Microbiology In Action
  Microbiology of the Intestinal Tract
    The Enterobacteriaceae (Enteric Bacilli)
      Identification of Pure Cultures of Enterobacteriaceae from the Normal Intestinal Flora
      Isolation Techniques for Enteric Pathogens
      Identification Techniques for Enteric Pathogens
      Serological Identification of Enteric Organisms
      Techniques to Distinguish Nonfermentative Gram-Negative Bacilli from Enterobacteriaceae
      Rapid Methods for Bacterial Identification
    Clinical Specimens from the Intestinal Tract
      Culturing a Fecal Sample
      Identification of an Unknown Enteric Organism
      Antimicrobial Susceptibility Test of an Enteric Organism

Purpose To study some enteric bacilli normally found in the bowel
Materials A stool specimen
Tubed sterile saline (0.5 ml)
EMB or MacConkey agar plate
Hektoen enteric (HE) agar plate
Blood agar plate

  1. Bring a fresh sample of your feces to the laboratory session. Collect it in a clean container fitted with a tight lid (a screwcap jar;waxed, cardboard cup; or plastic vessel).
  2. Using a swab, take up about 1 gm of feces (a piece the size of a large pea) and emulsify this in the tube of saline.
  3. Inoculate the fecal suspension, with the swab, on a blood agar, EMB or MacConkey agar plate, and a Hektoen enteric (HE) plate. Discard the swab in disinfectant solution. Streak for isolation, using a loop.
  4. Incubate the plates at 35°C for 24 hours.

  1. Describe the appearance of growth on your plate cultures.

  2. Interpret any difference in numbers of colonies on these plates.
  3. Interpret the color of colonies on EMB or MacConkey agar.
  4. Interpret the appearance of colonies on the HE plate.
  5. Were any lactose-negative colonies present? If so, name the genera to which they might belong and indicate the key procedures that would identify each.