Exam 2: Microbiology of UTI I DSA

Question 1

DSA checkpoints:

1. Anatomically, why are women and children at a higher risk to develop UTIs?

Answer 1

• 2 major factors:
  
  • the distance of the anus to the urinary tract
  • and the length of the urethra.
    
    • In women, the length of the urethra on average is 1.5 inches; however, in men, the average length is 8 inches.

Question 2

DSA checkpoints:

2. Why is the distance between the urinary tract and gastrointestinal tract a significant risk factor for UTIs?

Answer 2

• A direct comparison of male and female anatomy reveals the relatively short distance between the anus and urinary tract in women.
• The reason why this is significant is that the major causes of both community and nosocomial urinary tract infections comes from normal flora of the gastrointestinal tract.

Question 3

DSA checkpoints:

3. Sex is a risk factor for UTIs in both genders, but especially women. Why?

Answer 3

• Sex promotes the spread of normal flora, both vaginal and gastrointestinal.
• In addition, during sex, small microabrasions occur, which facilitate bacterial infections.
• Diaphragms, lubricants, douching, and spermicides can cause minor, unnoticeable damage, or alter the normal flora of the vagina, promoting urinary tract infections.
• Products that alter the pH of the vagina disrupt the normal flora of the vagina and also may promote the growth of more pathogenic bacteria.

Question 4

DSA checkpoints:

4. Inhibition of urine flow is a substantial risk factor for UTI.

What are some examples of conditions that inhibit this process?

Answer 4

• Inhibited flow of urine, whatever the cause, substantially increases the risk of UTIs across all groups.
• Pregnancy is a significant risk factor.
  
  • As the fetus grows, compression of the bladder and/or ureters can occur.
    
    • Inhibits flow of urine
• Vesicoureteral reflux
  
  • Urine flows backwards into the ureters due to the valve at the end of the ureter not closing properly.
• Catheters
• Urinary incontinence
• Kidney disease

Question 5

DSA checkpoints:

5. What is the difference between a complicated and an uncomplicated urinary tract infection?

Answer 5

• Uncomplicated UTI
  
  • no underlying health issues nor conditions that would facilitate a urinary tract infection
  • frequently handled with a short regiment of antibiotics and are relatively isolated incidences.
• Complicated UTI
  
  • Frequently, they are recurrent.
  • Some examples of contributing factors include:
    
    • An underlying anatomical abnormality that impairs the ability of the urinary tract to clear out urine and therefore bacteria (urinary incontinence, vesicoureteral reflux, obstruction (calculi), ect.)
    • medical conditions that predispose
      
      • Bladder and kidney dysfunction, or kidney transplant (especially in the first 3 months after transplant).
    • Catheter use in the hospital setting or chronic indwelling catheter in the outpatient setting

Question 6

DSA checkpoints:

6. What are some of the most common causes of UTIs in…

the community?

Nosocomial?

Answer 6

• Community acquired UTIs
  
  • E. Coli ! (80%)
  • Coagulase (-) Staphylococci (10%)
• Hospital (noscomiallly) acquired UTIs
  
  • E. Coli ! (40%)
  • other Gram (-) (25%)
  • other Gram (+) (16%)
  • Proteus mirabilis (11%)

Question 7

DSA checkpoints:

7. What are some of the common illnesses caused by E. coli?

Answer 7

• Depending on the virulence factors it possesses, E. coli can cause a variety of diseases including…
  
  • Meningitis: Especially in newborns, second only to Group B strep (S. agalactiae)
  • Urinary tract infections: The most common cause in both community and hospitals
  • Hospital-acquired pneumonia: A leading cause along with the other members of Enterobacteriaceae
  • Diarrhea: Several variations depending on the virulence factors present
  • Septicemia: One of the leading causes, due to LPS (endotoxin)

Question 8

DSA checkpoints:

8. What are the 3 antigens used to type E.coli and what structures are they associated with?

Answer 8

• There are 3 antigens used to type the family Enterobacteriaceae:
  
  • the O-antigen, K-antigen, and the H-antigen.
  • These antigens are associated with virulence factors and are used to classify the serotypes of the bacteria.
• O-antigen is a structural component of LPS.
• K-antigen is a component of the capsule possessed by members of Enterobacteriaceae.
  
  • E. coli doesn’t always have a capsule, thus it doesn’t always have a K antigen.
• H-antigen is a component of the flagella.

Question 9

DSA checkpoints:

9. EnteroPathogenic E. coli (EPEC)

Answer 9

• EPEC (pathogenic)
  
  • common cause of diarrhea in infants globally
  • frequently in developing countries.
  • EPEC possess a bundle-forming pili and several other adhesion proteins that allows it to attach to the lining of the gastrointestinal tract.
  • Upon attachment to the intestinal wall, EPEC causes the destruction of the microvilli lining the GI tract.
  • The formation of actin pedestals is a common trait of an EPEC infection, however it can occur in other E. coli strains as well.
  • Diarrhea caused by EPEC is typically watery and can be accompanied by fever and vomiting.
  • Disease is usually self-limiting, but dehydration is common risk factor that can become life threatening.
  • Occasionally, EPEC causes a chronic infection of the GI tract that must be cleared by antibiotics.

Question 10

DSA checkpoints:

9. EnteroToxigenic E. coli (ETEC) produces heat labile toxin and heat stable toxin.

How does this mediate disease pathology?

Answer 10

• ETEC (toxigenic)
  
  • caused when E. coli obtains 3 virulence factors:
    
    • heat labile toxin (LT)
    • heat stable toxin (ST)
    • and a pili for attachment to epithelial cells.
• ETEC uses the pili to attach itself to epithelial cells of the GI tract
  
  • then begins to secrete ST and LT. (disrupts osmolality)
    
    • The mechanism of each toxin compliments each other.
    • LT causes adenylate cyclase activity to increase, which increases cAMP.
      
      • This causes the levels of Cl^- to increase in the lumen, which pulls water into the gastrointestinal tract.
    • ST activates guanylate cyclase, increasing cGMP.
      
      • This causes decreased reabsorption of NaCl into the gastrointestinal tract, and subsequently, poor water absorption into the GI tract.
    • So, while LT pulls Cl- into the GI lumen, ST prevents NaCl from being reabsorbed.
      
      • This leads to a massive loss of water in the GI tract.
      • A severe infection by ETEC can cause a loss of up to 20 liters of water a day!
      • Because of the massive amount of water being lost, the stool will have the consistency and color of rice water, similar to cholera.

Question 11

DSA checkpoints:

10. EnteroHemorrhagic E. coli (EHEC) O157:H7 causes hemolytic uremic syndrome (HUS).

What toxin mediates this effect and how does it function?

Answer 11

• EHEC (Hemorrhagic)
  
  • Enterohemorrhagic E. coli (EHEC) possesses a pili for attachment just like ETEC
  • But instead of producing LT and ST, enterohemorrhagic E. coli produces a powerful Shiga-like toxin, also called verotoxin. (destroys cells)
• Shiga-like toxin inhibits the activity of the 60S subunit of ribosomes
  
  • just like the Shiga toxin produced by Shigella. After EHEC attaches to the epithelial cells lining the GI tract, the section of Shiga-like toxin causes the destruction of epithelial cells.
  • The diarrhea that results from EHEC is bloody and is accompanied by severe abdominal cramps.
    
    • This condition is referred to as hemorrhagic colitis.
• The most common stain of EHEC that frequently makes the rounds in the news is O157:H7.
  
  • Several outbreaks of O157:H7 have resulted from undercooked meat.
  • In addition, there is a particularly nasty complication typically seen in O157:H7: hemolytic uremic syndrome (HUS).
    
    • In HUS, anemia and thrombocytopenia accompany hemorrhagic colitis.
  • Renal failure is a common complication of a severe O157:H7 infection.
    
    • The leakage of verotoxin into the bloodstream results in destruction of endothelial cells, which can lead to renal failure.

Question 12

DSA checkpoints:

11. EnteroInvasive E. coli (EIEC) is similar to Shigella. How?

Hint: Invasion

Answer 12

• EIEC (Invasive)
• Very similar to Shigella because the main virulence factor is encoded on a plasmid that is shared by both Shigella and EIEC.
• Invades the epithelial cells lining the gastrointestinal wall and replicates within the cells.
  
  • This is in sharp contrast to EHEC and ETEC, which only attach to epithelial cells not invade them.
• EIEC triggers massive infiltration of leukocytes into the area to clear the intracellular infection. The diarrhea is typically bloody and full of puss as a result.
  
  • In addition, a fever usually accompanies the illness.

Question 13

DSA checkpoints:

12. How does E.coli appear on MacConkey and EMB agar?

Upon Gram staining?

Answer 13

• Gram stain is the first step in identifying E. coli.
  
  • E. coli is a Gram-_negative_ rod.
• In addition, E. coli is a lactose fermenting bacteria
  
  • Lactose-fermenting bacteria detected on either MacConkey agar or eosin methylene blue (EMB) agar.
    
    • EMB agar:
      
      • lactose-fermenting bacteria, like E. coli, appears as black colonies with a metallic-green sheen on EMB.
    • MacConkey agar:
      
      • lactose-fermenting bacteria, like E. coli, are stained pink.
      • Differentiating between fast (area around E.Coli on right of figure 7) and slow (middle bacteria on figure 7) lactose fermenters is a key way to tell Gram-negative bacteria apart!
• E. coli can covert tryptophan into indole and thus, is indole positive.
  
  • common way to distinguish between members of Enterobacteriaceae.
  • The bacteria is cultured in tryptophan broth.
    
    • If indole is generated, the media will turn pink after the addition of a detection reagent (Kovac’s reagent).

Question 14

DSA checkpoints:

13. How does the sputum look sometimes in patients with pneumonia due to K. pneumoniae?

Answer 14

• Pneumonia caused by K. pneumoniae is usually bloody
• has an appearance described as “red concurrent jelly sputum”.
  
  • A unique sputum appearance due to the production of a large mucoid polysaccharide capsule.

Question 15

DSA checkpoints:

14. Which risk factors contribute to respiratory infections by K. pneumoniae?

Answer 15

• K. pneumoniae is one of the leading causes of nosocomial pneumonia and urinary tract infections.
  
  • Like E.coli, K. pneumoniae is part of the normal flora of the gastrointestinal tract.
  • Sepsis is also a potent complication of invasive diseases caused by K. pneumoniae, but can also result from a contaminated IV line.
  • Complicating matter even further, members of Enterobacteriaceae are becoming carbapenem-resistant, making treatment very difficult.
    
    • About half of all patients who get septicemia from carbapenem-resistant bacteria will die.
    • Although both E.coli and K. pneumoniae can be carbapenem-resistant, resistance is much more common in K. pneumoniae.
  • K. pneumoniae is typically spread from person-to-person in a hospital setting due to poor hand washing but typically does not cause infections in immunocompetent patients.
• In addition to hospital patients, alcoholics are at a higher risk of getting pneumonia by K. pneumoniae.
• Patient who have seizures are also at risk for K. pneumoniae infections due to aspiration of salvia into the lungs.
• K. pneumoniae can cause a necrotizing pneumonia in severe cases, which can lead to cavity formation.

Question 16

DSA checkpoints:

15. What are the common ways to distinguish between E. coli and K. pneumoniae?

Answer 16

• Like E.coli, K. pneumoniae is a Gram-negative rod that ferments lactose.
• So how does one tell the difference between E. coli and K. pneumoniae?
  
  1. K. pneumoniae does not produce indole from tryptophan
     
     • E. coli is indole positive.
  2. In addition, the mucoid capsule produced by K. pneumoniae gives it a very distinct slimy appearance appearance in culture.
  3. Strains of Klebsiella are usually non-motile
     
     • while most strain of E. coli are motile.
  4. Klebsiella has a “red concurrent jelly sputum”

Question 17

DSA checkpoints:

16. One of the traits of a P. mirabilius urinary tract infection is an elevated urine pH.

Why does this occur?

Answer 17

• Another common cause of urinary tract infections, P. mirabilis is a member of the normal flora of the gastrointestinal tract.
• Normally the pH of urine is either neutral or slightly acidic (pH 4.6 to 8, roughly).
  
  • During a UTI, P. mirabilis causes the pH of the urine to rise.
• This occurs because P. mirabilis produces urease
  
  • which cleaves urea
    
    • forming carbon dioxide (CO₂) and ammonia (NH₃).
• (NH₂)2CO + H₂O → CO₂ + 2NH₃
• The alkaline pH can cause the precipitation of calcium-containing compounds.
• This results in an increased risk of both bladder and kidney stones.

Question 18

DSA checkpoints:

17. Which UTI-causing bacteria produce urease?

Which do not?

Answer 18

• Bacteria that cause UTIs and produce urease.
  
  • K. pneumoniae
  • S. saprophyticus
  • U. urealyticum
  • P. aeruginosa
  • S. epidermidis all can cause UTIs and all produce urease.
• Interestingly, E. coli strains typically do not produce urease, thus can be distinguished from other UTI-causing bacteria.

Question 19

DSA checkpoints:

18. How do urease-producing bacteria contribute to kidney and bladder stones formation?

Answer 19

• bacteria produces urease
  
  • which cleaves urea
    
    • forming carbon dioxide (CO₂) and ammonia (NH₃).
    • (NH₂)2CO + H₂O → CO₂ + 2NH₃
• The alkaline pH can cause the precipitation of calcium-containing compounds.
  
  • This results in an increased risk of both bladder and kidney stones

Question 20

DSA checkpoints:

19. Proteus colonies are very unique looking.

How?

Answer 20

• P. mirabilius is incredibly mobile. “ Swarming motility“
  
  • This mobility along with its ability to cleave urea makes P. mirabilis particular adept at rising through the urinary tract.
• When cultured on an agar, most mobile bacteria will not move away from the place they were seeded because semi-solid agars are hard to move through.
• As colonies of P. mirabilis grow, they will move across the agar forming bull’s eyes.

Question 21

DSA checkpoints:

20. What common traits are used to distinguish between E. coli, K. pneumoniae, P. mirabilius, and P. aeruginosa?

Use figure 10 along with urease production.

Answer 21

Question 22

Pseudomonas aeruginosa

Answer 22

• Gram-negative rod
• does not ferment lactose
• oxidase positive
• Pseudomonas produces pigments
  
  • gives it an aqua color in culture
• has a sweet, grape-like smell
• While Pseudomonas typically doesn’t cause UTI in health people, Pseudomonas is a common cause of complicated urinary tract infections, usually in a hospital setting.