Intro to Bacterial UTIs - Diebel

Question 1

What are the five major defenses of the Urinary Tract?

Answer 1

1. Flushing action of urine flow (sloughing epithelial cells)
2. Mucosa → secrete IgA (adaptive immunity)
3. Urine chemistry
   
   1. Acidity
   2. Lysozymes (lyse peptidoglycan & cell walls)
   3. Lactoferrin (iron stealing → slows growth of bacteria)
4. Surface proteins
5. Normal flora (outcompete pathogenic species)

Question 2

What are the major microbial and immunological threats to the urinary system?

Answer 2

• Normal biota → OPPORTUNISTIC bugs
  
  • often from GI tract
• Catheter insertion
  
  • hospital acquired
• Glomerulonephritis
  
  • Strep pyogenes from skin/throat

Question 3

What are the five most common causative agents in UTIs?

Answer 3

• Escherichia coli
• Staphylococcus saprophyticus
• Enterococcus species
• Klebsiella pneumoniae
• Proteus mirabilis

Question 4

~95% of UTI cases are caused by what type of bacteria?

Answer 4

normal biota of the GI tract

Question 5

What is the prevalence of community acquired Acute Urinary Tract Infections?

Answer 5

6-8 million cases of community acquired UTIs in the US per year

Question 6

What is the overal incidence of Urinary Tract Infections in young women?

Answer 6

0.5-0.7 episodes per year

(“reocurring” in 25%-30%)

Question 7

What are the two biggest risk factors for UTI?

Answer 7

• Recent sexual intercourse
• Catheterization

Question 8

What abnormalities can presdispose children to UTIs?

Answer 8

anatomical or functional abnormalities of the urinary tract

Question 9

What abnormalities can presdispose men to UTIs?

Answer 9

• Underlying urinary tract abnormality
  
  • enlarged prostate → obstruction
    
    • can also lead to prostatitis & epidydimitis

Question 10

What is E.coli colonization dependent on in UTIs?

Answer 10

• specific adhesions on the ends of long fimbriae (recognized by TLR4)
  
  • P fimbriae
  • Type 1 fimbriae
• motility

Question 11

What is the normal mechanism of “transmission” of E.coli in UTIs?

Answer 11

• Not typically from person to person
• More often from organ to organ!
  
  • women: anus → urethra
    
    • up to 10x-50x more likely

Question 12

What are nosocomial infections due to E.coli, K. pneumoniae, carbapenem-resistant Enterobacteriaceae (CRE), or vancomycin-resistant enterococci (VRE) associated with?

Answer 12

Urinary catheters

Question 13

What three things are helpful to prevent UTIs?

Answer 13

• Regular urination
• Good hygiene
• Drink cranberry juice
  
  • potentially blocks bacterial attachment to the epithelium
• _{Vaccines in clinical trial.}

Question 14

What two laboratory findings are diagnostic in Uncomplicated UTIs?

Answer 14

• Pyuria = 10+ neutrophils per high-power field of unspun, voided midstream urine
• Bacteriuria = >10⁵ colony-forming units (cfu) per mL of urine obtained from clean-voided midstream urine

Question 15

In complicated UTIs, colony counts (colony-forming units) can be much _______ for diagnosis?

Answer 15

LOWER

Question 16

What does selective media contain?

Answer 16

• Compounds that selectively inhibit growth of some microbes, but not others.

Question 17

What does differential media contain?

Answer 17

• An indicator (usually a dye)
  
  • detects particular chemical reactions occurring during growth

Question 18

What quick and easy test can you use to differentiate between Staph or Strep?

Answer 18

Catalase Test

• Catalase (+) = Staph
• Catalase (–) = Strep

Question 19

How do you test for catalase activity?

Answer 19

• Put small drop of bacteria into hydrogen peroxide
  
  • if catalase present → rapid release of oxygen bubbles
    
    • catalase converts H₂O₂ into H₂O + O₂
  • if catalase absent → weak/lack of buble production

Question 20

What test can you use to differentiate between Staph aureus vs. Staph saprophyticus?

Answer 20

• Coagulase test
  
  • Staph aureus = coag +
  • Staph saprophyticus = coag –

Question 21

How do you test for coagulase activity?

Answer 21

• Add bacteria to plasma
  
  • clot forms if bound coagulase or “clumping factor” is on the bacterial cell wall
  • reacts directly with fibrinogen causing cells to clump

Question 22

If both bacteria are coagulase negative, how can you differentiate between Staph epidermidis or Staph saprophyticus?

Answer 22

• Novobiocin (drug) Sensitivity
  
  • Staph epidermidies = sensitive
    
    • ring indicates inhibition of growth
  • Staph saprophyticus = resistant
    
    • no ring/disturbance in bacterial growth

Question 23

When should you avoid treating with Nitrofurantoin?

Answer 23

• Suspected pyelonephritis
  
  • due to poor upper urinary tract penetration

Question 24

When should you use TMP-SMX to treat a UTI?

Answer 24

• If local prevalence of E.coli resistence to TMP-SMX is less than or equal to 20%
• If has not been used to treat a UTI in the last 3 months

Question 25

What are the recommended alternative treatments for UTI?

Answer 25

* Fluoroquinolones = Ciprofloxacin/Norfloxacin * Amoxicillin/Clavulanate

Question 26

When is it appropriate to treat a UTI with Fluoroquinolones? (Hint: 4 reasons)

Answer 26

* With severe symptoms * Allergy to 1st line treatments * TMP-SMX used in the last 3 months for UTI * Infection acquired in locality with greater than 20% resistance to TMP-SMX

Question 27

When is Amoxicillin/clavulanate a first line treatment for UTI?

Answer 27

UTI due to Staph saprophyticus

Question 28

What UTI antibiotic treatment should NOT be used empirically?

Answer 28

Amoxicillin/clavulanate

Question 29

What type of infection usually presents with vaginal itching, and discharge described as white, cottage cheese-like discharge starting soon after course of oral antibiotics?

Answer 29

Yeast infection =\> due to Candida

Question 30

What type of infection causes yellow, frothy discharge?

Answer 30

trichomoniasis

Question 31

What color does beta-hemolysing bacteria turn blood agar?

Answer 31

Gold → complete hemolysis/digestion of RBC (e.g. Staph aureus)

Question 32

What color does alpha-hemolysing bacteria turn blood agar?

Answer 32

Green or brown → partical lysing of RBC | (e.g. Strep pneumoniae/viridans)

Question 33

What color does gamma-hemolysing bacteria turn blood agar?

Answer 33

Pink → non-hemolytic (e.g. Staph saprophyticus, Enterococcus)

Question 34

What is MacConkey agar used for?

Answer 34

selectively isolate Gram-negative and enteric (normally found in the intestinal tract) bacilli and differentiate them based on lactose fermentation * contains bile salts → inhibits Gram (+) * Using neutral red pH indicator: * utilize lactose =\> makes acid/lowers pH =\> pink colonies * e.g. E.coli, Klebsiella * Non-Lactose fermenting =\> makes ammonia/raises pH =\> white or colorless colonies * e.g. Proteus species