ENTERO

• Genus


  A taxonomic category that ranks above species and below family
• Overt Pathogens


  Organisms that really cause infection in the GI tract
• Opportunistic Pathogens


  Enteric organisms that are considered part of the normal flora in the GI tract, but can cause infection outside the GI tract
• Opportunistic pathogens are the common causes of pneumonia, meningitis, urinary tract infection, sepsis/septicemia, and wound infections
• Overt Pathogens


  • Shigella
  • Salmonella
  • Yersinia
• Lactose Fermenters (Opportunistic Pathogens)

  • Escherichia
  • Enterobacter
  • Hafnia
  • Citrobacter
  • Erwinia
  • Proteus
  • Klebsiella
  • Serratia
  • Edwardsiella
• Non-Lactose Fermenters (Overt Pathogens)

  • Shigella
  • Salmonella
  • Yersinia
• Isolation and identification of enteric organisms

  1. Isolate the organism using correct culture media

  2. Demonstration of characteristic colonies on culture media

  3. Demonstrate the biochemical reactions from the characteristic colonies
• Differential, Mildly/Slightly Selective Media

  Promotes the growth of gram (-) organisms, but inhibits the growth of gram (+) organisms. Cannot isolate pure organisms.
• Differential, Moderately Selective Media

  Isolates true pathogens/overt pathogens. Inhibits gram (+) organisms and other organisms other than true enteric pathogens. Only allows growth of Shigella, Yersinia, and Salmonella.
• Highly Selective Media


  Allows the growth of specific enteric organisms. Only allows the growth of one organism; does not need to differentiate organisms anymore.
• Differential, Mildly Selective Media

  • Eosin-Methylene Blue Agar (EMB Agar)
  • MacConkey Agar
• Differential, Moderately Selective Media

  • Salmonella Shigella Agar
  • Hektoen-Enteric Agar (HE, HEA, or HEK)
  • Xylose Lysine Desoxycholate/Deoxycholate Agar
• Highly Selective Media


  • Bismuth Sulfite Agar
• Shigella


  Produce colorless colonies on HEK, but because of its base color green, when colonies are viewed, they appear green. Colonies are perceived as green because it is growing on top of a green colored medium.
• Uninoculated


  • Turbid and green
• Xylose Lysine Desoxycholate/Deoxycholate Agar

  Suitable for Shigella
• Sugars in Xylose Lysine Desoxycholate/Deoxycholate Agar

  • Lactose, sucrose, and xylose
• pH indicator in Xylose Lysine Desoxycholate/Deoxycholate Agar

  Phenol red
• H2S indicator in Xylose Lysine Desoxycholate/Deoxycholate Agar

  Sodium thiosulfate and ferric ammonium citrate (responsible for differential property)
• Inhibitor in Xylose Lysine Desoxycholate/Deoxycholate Agar

  Sodium deoxycholate (selective property)
• Lysine in Xylose Lysine Desoxycholate/Deoxycholate Agar

  An amino acid responsible for detecting salmonella reaction
• Shigella on Xylose Lysine Desoxycholate/Deoxycholate Agar


  Red colonies without black centers
• Bismuth Sulfite Agar


  Highly selective medium for isolation of S. typhi
• H2S indicator in Bismuth Sulfite Agar

  Bismuth sulfite and ferrous sulfate
• Inhibitor in Bismuth Sulfite Agar


  Brilliant green
• S. typhi on Bismuth Sulfite Agar


  Jet-black colonies with metallic sheen
• Investigation of an unknown isolate or investigation of an unknown organism in microbiology laboratory or bacteriology laboratory entails knowing the causative agent of the infection of the patient.
• Three basic steps


  1. Microscopic evaluation

  2. Identification of the correct culture medium or culture media

  3. Biochemical reactions
• Microscopic examination


  To identify what culture medium or cultural media to use in the isolation of the organism causing infection to that specimen
• Use the appropriate culture medium or culture media

  Four Quadrant Streak Plate Method (qualitative) is frequently used because it is the method of isolating pure colonies
• If the four quadrants do not show any colonies or apparent growth, then proceed to the next quadrant which is the third quadrant
• If the third quadrant does not show any growth, proceed to the second quadrant and never use the colonies in the first quadrant
• The first quadrant is always understood to contain both the organism of interest and the contaminants
• Sterile specimen


  A type of specimen where it contains only the organism that's really causing the infection
• Non-sterile specimen


  A specimen that will harbor other normal flora in addition to the organism of interest
• When heating the wire loop in between quadrants for a non-sterile specimen, you are increasing the chance of killing the contaminants and also increasing the chance of isolating the organism of interest
• Inoculate the proper or appropriate cultured medium or culture media

  So that isolation of the organism of interest can be obtained at the end of the investigation
• Incubate the cultural media

  At 37 degrees Celsius for 24 hours
• The third step in the investigation of unknown organism will only come into play once colonies are already seen in the culture media