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Questions and Answers
What is a major health risk associated with E. coli in immunocompromised individuals?
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?
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?
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?
Which culture medium is specifically used to grow E. coli?
What type of bacteria primarily belongs to Enterobacteriaceae group?
What type of bacteria primarily belongs to Enterobacteriaceae group?
What is the result of adherence of Enteropathogenic E. coli (EPEC) to the mucosa?
What is the result of adherence of Enteropathogenic E. coli (EPEC) to the mucosa?
What is the main metabolic characteristic of the Enterobacteriaceae group?
What is the main metabolic characteristic of the Enterobacteriaceae group?
What common biochemical test result is positive for E. coli?
What common biochemical test result is positive for E. coli?
Which antigen is associated with strains of E. coli causing meningitis?
Which antigen is associated with strains of E. coli causing meningitis?
What color would indicate an acidic environment in the tests described?
What color would indicate an acidic environment in the tests described?
In the Triple Sugar Iron Test, what does a red/yellow result signify?
In the Triple Sugar Iron Test, what does a red/yellow result signify?
What does a yellow/yellow result in the tests indicate?
What does a yellow/yellow result in the tests indicate?
Which factor influences the aerobic reactions during the inoculation of slants?
Which factor influences the aerobic reactions during the inoculation of slants?
What role does phenol red play in the tests mentioned?
What role does phenol red play in the tests mentioned?
What reaction occurs in the butt of the medium during the inoculation by stab?
What reaction occurs in the butt of the medium during the inoculation by stab?
What color change indicates lactose fermentation in MacConkey agar?
What color change indicates lactose fermentation in MacConkey agar?
What type of organisms does MacConkey agar selectively promote growth for?
What type of organisms does MacConkey agar selectively promote growth for?
Which enzyme is responsible for the rapid entry of lactose into cells for fermenting organisms?
Which enzyme is responsible for the rapid entry of lactose into cells for fermenting organisms?
What is the appearance of lactose non-fermenting strains on MacConkey agar?
What is the appearance of lactose non-fermenting strains on MacConkey agar?
What inhibits the growth of Gram positive organisms on MacConkey agar?
What inhibits the growth of Gram positive organisms on MacConkey agar?
What does neutral red in MacConkey agar indicate?
What does neutral red in MacConkey agar indicate?
Which of the following is a delayed lactose fermenter?
Which of the following is a delayed lactose fermenter?
Why is lactose included in MacConkey agar?
Why is lactose included in MacConkey agar?
What happens if an organism lacks B-galactoside permease?
What happens if an organism lacks B-galactoside permease?
Which morphological form do most gram negative organisms exhibit on MacConkey agar?
Which morphological form do most gram negative organisms exhibit on MacConkey agar?
What type of diarrhea is associated with STEC infections?
What type of diarrhea is associated with STEC infections?
What is the primary mechanism through which E. coli causes illness?
What is the primary mechanism through which E. coli causes illness?
Which strain of E. coli is most commonly associated with foodborne illnesses?
Which strain of E. coli is most commonly associated with foodborne illnesses?
What is the primary reason E. coli can cause urinary tract infections (UTIs)?
What is the primary reason E. coli can cause urinary tract infections (UTIs)?
Which antigen is a part of the complex antigenic structure of E. coli?
Which antigen is a part of the complex antigenic structure of E. coli?
What type of morphology does E. coli exhibit?
What type of morphology does E. coli exhibit?
Which of the following is NOT a characteristic of E. coli?
Which of the following is NOT a characteristic of E. coli?
E. coli is responsible for what percentage of UTIs in women?
E. coli is responsible for what percentage of UTIs in women?
What role does Shiga-like toxin play in E. coli infections?
What role does Shiga-like toxin play in E. coli infections?
Which is a feature of E. coli's flagella?
Which is a feature of E. coli's flagella?
What does a red color change indicate in the biochemical tubes?
What does a red color change indicate in the biochemical tubes?
What does a yellow butt indicate in the biochemical tubes?
What does a yellow butt indicate in the biochemical tubes?
Which combination of conditions leads to a yellow slant in the results?
Which combination of conditions leads to a yellow slant in the results?
When reading results from the biochemical tubes, which parts must be observed?
When reading results from the biochemical tubes, which parts must be observed?
What is the significance of transferring growth from MacConkey agar to biochemical tubes?
What is the significance of transferring growth from MacConkey agar to biochemical tubes?
What does a color change to yellow in the slant and butt generally represent?
What does a color change to yellow in the slant and butt generally represent?
What is indicated by a combination of red slant and yellow butt?
What is indicated by a combination of red slant and yellow butt?
Why is it important to read both the slant and butt when analyzing results?
Why is it important to read both the slant and butt when analyzing results?
What does it suggest if both the slant and butt remain red?
What does it suggest if both the slant and butt remain red?
What is the purpose of MacConkey agar in this process?
What is the purpose of MacConkey agar in this process?
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.
- Mechanism: production of toxins:
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.
- Phenol Red: pH indicator.
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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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.
