ENTERICS

• Genus


  A taxonomic category ranking below a family and above a species, comprising structurally or genetically related organisms
• Overt Pathogens


  Enteric 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 (LF)


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


  • 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. It cannot isolate pure organisms.
• Differential, Moderately Selective Media

  Isolates true pathogens/overt pathogens. They inhibit 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. It only allows the growth of one organism; does not need to differentiate organisms anymore.
• Eosin-Methylene Blue Agar (EMB Agar)


  • Contains lactose and sucrose, differentiates lactose fermenters from non-lactose fermenters, slightly selective for isolation of gram (-) intestinal bacteria, contains eosin y and methylene blue as pH indicators

  
• MacConkey Agar


  • Differential, slightly selective medium for gram (-) intestinal bacteria, differentiates lactose fermenters from non-lactose fermenters, contains lactose, bile salts and crystal violet as inhibitors

  
• Salmonella Shigella Agar


  • Primarily for Salmonella, moderately selective medium, contains lactose, neutral red as pH indicator, ferric ammonium citrate and sodium thiosulfate as H2S indicators, sodium citrate, brilliant green and bile salts as inhibitors

  
• Hektoen-Enteric Agar (HE, HEA, or HEK)

  • Moderately selective medium, contains lactose, sucrose and salicin as sugars, acid fuchsin and bromthymol blue as pH indicators, ferric ammonium citrate and sodium thiosulfate as H2S indicators, bile salts as inhibitor
• Xylose Lysine Desoxycholate/Deoxycholate Agar


  • Suitable for Shigella, contains lactose, sucrose and xylose as sugars, phenol red as pH indicator, sodium thiosulfate and ferric ammonium citrate as H2S indicators, sodium deoxycholate as inhibitor, lysine for detecting Salmonella reaction

  
• Bismuth Sulfite Agar


  • Highly selective medium for isolation of S. typhi, contains glucose, bismuth sulfite and ferrous sulfate as H2S indicators, brilliant green as inhibitor
• Oxycholate/Deoxycholate Agar


  Suitable for Shigella
• Sugars in Oxycholate/Deoxycholate Agar

  • lactose, sucrose, and xylose
• pH indicator in Oxycholate/Deoxycholate Agar

  phenol red
• H2S indicator in Oxycholate/Deoxycholate Agar


  sodium thiosulfate and ferric ammonium citrate (responsible for differential property)
• Inhibitor in Oxycholate/Deoxycholate Agar


  sodium deoxycholate (selective property)
• Lysine in Oxycholate/Deoxycholate Agar


  an amino acid responsible for detecting salmonella reaction

  
• Shigella on Oxycholate/Deoxycholate Agar


  red colonies without black centers
• Oxycholate/Deoxycholate Agar is a HIGHLY SELECTIVE MEDIA
• 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
• The basic steps in the investigation of an unknown isolate or organism in a microbiology/bacteriology laboratory are:
• The four quadrant streak plate method is frequently used to isolate pure colonies
• Sterile specimen


  Contains only the organism causing the infection, no contaminants
• Non-sterile specimen


  Contains both the organism of interest and contaminants
• Four quadrant streak plate method

  • If no growth in 4th quadrant, proceed to 3rd, then 2nd, never use 1st quadrant which contains both organism of interest and contaminants

  If specimen is sterile, don't heat loop between quadrants

  If specimen is non-sterile, heat loop between quadrants to kill contaminants
• Sputum is an example of a non-sterile specimen
• Investigation of an unknown organism

  Inoculate proper culture medium/media

  2. Incubate at 37°C for 24 hours

  3. Perform biochemical testing on isolated colonies
• Enterobacteriaceae


  Also known as "enterics" or "enteric organisms"
• Two different types of Enterobacteriaceae

  • Opportunistic Pathogens (Coliforms)

  Overt Pathogens or True Pathogens
• Opportunistic Pathogens (Coliforms)


  • Normal flora in GI tract, cause infections outside GI tract like pneumonia, meningitis, UTI, wound infection, septicemia
• Overt Pathogens or True Pathogens

  • Cause GI tract infections, transmitted via fecal-oral route