Enterobacteriaceae and E.coli Overview
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Questions and Answers

What is a major health risk associated with E. coli in immunocompromised individuals?

  • Meningitis
  • Gastroenteritis
  • Dehydration
  • Sepsis (correct)

    • Which E. coli serotype is often associated with severe cases of sepsis?

  • E. coli K1
  • E. coli EPEC
  • E. coli O25b/ST131 (correct)
  • E. coli O157:H7

    • What characteristic differentiates E. coli from nonmotile Gram negative bacteria like Shigella?

  • Ability to ferment lactose
  • Presence of peritrichous flagella (correct)
  • Formation of K1 antigen
  • Production of hydrogen gas

    • Which culture medium is specifically used to grow E. coli?

    <p>MacConkey agar</p> Signup and view all the answers

    What type of bacteria primarily belongs to Enterobacteriaceae group?

    <p>Gram negative rods</p> Signup and view all the answers

    What is the result of adherence of Enteropathogenic E. coli (EPEC) to the mucosa?

    <p>Flattening of villi</p> Signup and view all the answers

    What is the main metabolic characteristic of the Enterobacteriaceae group?

    <p>Fermentation of glucose</p> Signup and view all the answers

    What common biochemical test result is positive for E. coli?

    <p>Catalase positive</p> Signup and view all the answers

    Which antigen is associated with strains of E. coli causing meningitis?

    <p>K1 antigen</p> Signup and view all the answers

    What color would indicate an acidic environment in the tests described?

    <p>Yellow</p> Signup and view all the answers

    In the Triple Sugar Iron Test, what does a red/yellow result signify?

    <p>Only glucose is fermented</p> Signup and view all the answers

    What does a yellow/yellow result in the tests indicate?

    <p>All sugars have been fermented</p> Signup and view all the answers

    Which factor influences the aerobic reactions during the inoculation of slants?

    <p>Exposed surface area to air</p> Signup and view all the answers

    What role does phenol red play in the tests mentioned?

    <p>Acts as a pH indicator</p> Signup and view all the answers

    What reaction occurs in the butt of the medium during the inoculation by stab?

    <p>Anaerobic reactions occur</p> Signup and view all the answers

    What color change indicates lactose fermentation in MacConkey agar?

    <p>Pink</p> Signup and view all the answers

    What type of organisms does MacConkey agar selectively promote growth for?

    <p>Gram negative organisms</p> Signup and view all the answers

    Which enzyme is responsible for the rapid entry of lactose into cells for fermenting organisms?

    <p>B-galactoside permease</p> Signup and view all the answers

    What is the appearance of lactose non-fermenting strains on MacConkey agar?

    <p>Colorless and transparent</p> Signup and view all the answers

    What inhibits the growth of Gram positive organisms on MacConkey agar?

    <p>Bile salts and crystal violet</p> Signup and view all the answers

    What does neutral red in MacConkey agar indicate?

    <p>Acid production from lactose</p> Signup and view all the answers

    Which of the following is a delayed lactose fermenter?

    <p>Klebsiella pneumoniae</p> Signup and view all the answers

    Why is lactose included in MacConkey agar?

    <p>To provide a source of fermentable carbohydrate</p> Signup and view all the answers

    What happens if an organism lacks B-galactoside permease?

    <p>It absorbs lactose slowly</p> Signup and view all the answers

    Which morphological form do most gram negative organisms exhibit on MacConkey agar?

    <p>Rods (bacilli)</p> Signup and view all the answers

    What type of diarrhea is associated with STEC infections?

    <p>Severe watery diarrhea</p> Signup and view all the answers

    What is the primary mechanism through which E. coli causes illness?

    <p>Production of toxins</p> Signup and view all the answers

    Which strain of E. coli is most commonly associated with foodborne illnesses?

    <p>O157:H7</p> Signup and view all the answers

    What is the primary reason E. coli can cause urinary tract infections (UTIs)?

    <p>Certain O serotypes have pili for adhesion</p> Signup and view all the answers

    Which antigen is a part of the complex antigenic structure of E. coli?

    <p>Capsule (K) antigen</p> Signup and view all the answers

    What type of morphology does E. coli exhibit?

    <p>Gram negative bacilli</p> Signup and view all the answers

    Which of the following is NOT a characteristic of E. coli?

    <p>Gram positive cocci</p> Signup and view all the answers

    E. coli is responsible for what percentage of UTIs in women?

    <p>90%</p> Signup and view all the answers

    What role does Shiga-like toxin play in E. coli infections?

    <p>Causes cell damage and disease symptoms</p> Signup and view all the answers

    Which is a feature of E. coli's flagella?

    <p>Peritrichous flagella</p> Signup and view all the answers

    What does a red color change indicate in the biochemical tubes?

    <p>Alkaline conditions (K)</p> Signup and view all the answers

    What does a yellow butt indicate in the biochemical tubes?

    <p>Only glucose is fermented</p> Signup and view all the answers

    Which combination of conditions leads to a yellow slant in the results?

    <p>Fermentation of glucose, lactose, and/or sucrose</p> Signup and view all the answers

    When reading results from the biochemical tubes, which parts must be observed?

    <p>Both the slant and the butt</p> Signup and view all the answers

    What is the significance of transferring growth from MacConkey agar to biochemical tubes?

    <p>For further differentiation of Enteric bacilli</p> Signup and view all the answers

    What does a color change to yellow in the slant and butt generally represent?

    <p>Fermentation of glucose, lactose, and/or sucrose</p> Signup and view all the answers

    What is indicated by a combination of red slant and yellow butt?

    <p>Glucose fermented, but lactose not fermented</p> Signup and view all the answers

    Why is it important to read both the slant and butt when analyzing results?

    <p>To gain insight into fermentation patterns</p> Signup and view all the answers

    What does it suggest if both the slant and butt remain red?

    <p>No carbohydrate fermentation occurred</p> Signup and view all the answers

    What is the purpose of MacConkey agar in this process?

    <p>To inhibit the growth of gram-positive bacteria</p> Signup and view all the answers

    Study Notes

    Enterobacteriaceae group

    • Most common group of Gram-negative rods cultured in clinical labs.
    • Can reduce nitrate to nitrite.
    • Natural habitat: intestinal tract of humans and animals.
    • Either motile (E.coli) with peritrichous flagella, or non-motile (Shigella and Klebsiella).
    • Grow well on MacConkey agar.
    • Facultative anaerobes: ferment rather than oxidize glucose, often with gas production.
    • Catalase: positive.
    • Cytochrome oxidase: negative.
    • Complex antigenic structure.

    Escherichia coli

    • Morphology: Gram-negative bacilli.
    • Motile due to the presence of Peritrichous flagella.
    • Complex antigenic structure:
      • Capsule (K) antigen.
      • LPS (O) or Somatic (O) antigen.
      • Fimbriae (F) antigen.
    • Produce toxins.

    Diseases caused by E.coli

    • Manifestation depends on the site of infection.

    Urinary Tract Infection (UTI)

    • Most common cause of UTI in 90% of women.
    • Caused by certain O serotypes.
    • Strains have pili that help them adhere to specific receptors on the urinary tract epithelium.

    Sepsis

    • Blood: entry of E.coli will cause sepsis, especially in immunocompromised individuals.
    • Often, the major clone associated is E.coli O25b/ST131.

    Meningitis

    • Meninges: caused by strains of E.coli having K1 antigen ("K" stands for capsular antigen).

    E.coli associated diarrheal diseases

    • Enteropathogenic E.coli (EPEC): severe water diarrhea in infants.
      • Mechanism: adherence of EPEC to the mucosa and flattening of the villi.
    • Enterotoxigenic E.coli (STEC): mild non-bloody diarrhea, hemorrhagic colitis, hemolytic uremic syndrome.
      • Mechanism: production of toxins:
        • Shiga-like toxin 1.
        • Shiga-like toxin 2.
      • O157:H7 is the most common strain.

    Culture medium: MacConkey agar

    • Selective and differential.
    • Enterobacteriaceae group grow well in MacConkey agar because it is selective for Gram-negative organisms, and most Gram-negative organisms have a rod-shaped morphology (bacilli).
    • Bile salts and crystal violet inhibit the growth of Gram-positive organisms.
    • Lactose provides a source of fermentable carbohydrate, allowing for differentiation.
    • pH indicator: Neutral red.

    Lactose fermenting strains

    • Pink.
    • Production of acid from lactose: Neutral red changes color when the pH is below 6.8.

    Lactose non-fermenting strains

    • Colorless and transparent.

    Biochemical testing

    • Used for further differentiation of Enteric bacilli.
    • After growth in MacConkey agar, it will be transferred to biochemical tubes for inoculation.
    • Triple Sugar Iron agar, Lysine Iron Agar, Citrate and Urease: solid tubes.
    • Sulfide Indole Motility: semi-solid.

    Triple Sugar Iron Test

    • Composition:
      • Protein sources: peptone, beef and yeast extract.
      • Sugars: 1% lactose, 1% sucrose, 0.1% glucose.
    • Indicator:
      • Phenol Red: pH indicator.
        • Alkaline: Red.
        • Acidic: Yellow.
      • Ferrous sulfate/ Ferrous ammonium sulfate: hydrogen sulfide (H2S) production.

    MacConkey agar: Growth pattern of some Enterobacteriaceae

    • Lactose fermenter, Lactose fermenter, Non-Lactose fermenter
    • Lactose fermentation:
      • Lactose fermenters: B-galactoside permease (a transport protein in the wall) facilitates the fast entry of lactose into the cell, turning the agar pink at pH 6.8.
      • Late or Delayed lactose fermenters: Only have B-galactosidase.
    • How to detect fermentation in Mac?
      • Observe the color changes in the broth after inoculation.
      • Red color: Alkaline (K).
      • Yellow color: Acidic (A).
        • If yellow butt only: only glucose is fermented.
        • If yellow slant: glucose, lactose, and/or sucrose are fermented.

    Reading Results

    • Read both slant and butt. Observe the color changes:
      • Yellow: Acidic (A)
      • Red: Alkaline (K)
      • For example:
        • Alkaline slant/acid butt = red/yellow = K/A (only glucose is fermented).
        • Acid slant/acid butt = yellow/yellow = A/A (glucose, lactose and/or sucrose are fermented).

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    Biochemical Study of E. Coli PDF

    Description

    Explore the characteristics and clinical significance of the Enterobacteriaceae group, focusing on Escherichia coli. This quiz covers its morphology, antigenic structure, and the diseases it causes, particularly urinary tract infections. Gain insights into how these bacteria interact with their environments and affect human health.

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