Identification Techniques for Enteric Pathogens


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 biochemical reactions of Salmonella and Shigella
Materials TSI slants
SIM tubes
MR-VP broths
Simmons citrate slants
Urea broth tubes
Phenylalanine agar slants
Lysine and ornithine decarboxylase broths
Mineral oil in dropper bottle
Sterile 1.0-ml pipettes
Pipette bulb or other aspiration device
Sterile empty tubes
Kovac’s reagent
Methyl red indicator
5% alphanaphthol
40% sodium or potassium hydroxide
10% ferric chloride
Agar slant cultures of Salmonella and Shigella species

  1. You will be assigned a culture of either Salmonella or Shigella. Inoculate one tube of each medium provided (i.e.:TSI; SIM; MR-VP broth; citrate slant; urea, lysine, and ornithine broths; and phenylalanine agar).
  2. Incubate all tubes at 35°C for 24 hours.
  3. Complete the IMViC and PD tests (see Experiment 24.1). Read and record all biochemical reactions under Results. Observe your neighbors’ results and record all information for both organisms.

Purpose To illustrate identification of a microorganism by the slide agglutination technique
Materials Glass slides
70% alcohol
Saline (0.85%)
Capillary pipettes
Heat-killed suspension of E. coli or Salmonella
E. coli or Salmonella antiserum

  1. Carefully wash a slide in 70% alcohol and let it air dry..
  2. Using a glass-marking pen or pencil, draw two circles at opposite ends of the slide..
  3. Using a capillary pipette, place a drop of saline in one circle. Mark this circle “C,” for control..
  4. With a fresh capillary pipette, place a drop of antiserum in the other circle..
  5. Use another pipette to add a drop of heat-killed bacterial suspension (this is the antigen) to the material in each circle..
  6. Pick up the slide by its edges, with your thumb and forefinger, and rock it gently back and forth for a few seconds..
  7. Hold the slide over a good light and observe closely for any change in the appearance of the suspension in the two circles.

  1. In the following diagram indicate any visible difference you observed in the suspensions at each end of the slide. 192 Diagnostic Microbiology in Action
  2. State your interpretation of the result.