Intro to Bacterial UTIs - Diebel Flashcards
What are the five major defenses of the Urinary Tract?
- Flushing action of urine flow (sloughing epithelial cells)
- Mucosa → secrete IgA (adaptive immunity)
-
Urine chemistry
- Acidity
- Lysozymes (lyse peptidoglycan & cell walls)
- Lactoferrin (iron stealing → slows growth of bacteria)
- Surface proteins
- Normal flora (outcompete pathogenic species)
What are the major microbial and immunological threats to the urinary system?
- Normal biota → OPPORTUNISTIC bugs
- often from GI tract
- Catheter insertion
- hospital acquired
- Glomerulonephritis
- Strep pyogenes from skin/throat
What are the five most common causative agents in UTIs?
- Escherichia coli
- Staphylococcus saprophyticus
- Enterococcus species
- Klebsiella pneumoniae
- Proteus mirabilis
~95% of UTI cases are caused by what type of bacteria?
normal biota of the GI tract
What is the prevalence of community acquired Acute Urinary Tract Infections?
6-8 million cases of community acquired UTIs in the US per year
What is the overal incidence of Urinary Tract Infections in young women?
0.5-0.7 episodes per year
(“reocurring” in 25%-30%)
What are the two biggest risk factors for UTI?
- Recent sexual intercourse
- Catheterization
What abnormalities can presdispose children to UTIs?
anatomical or functional abnormalities of the urinary tract
What abnormalities can presdispose men to UTIs?
- Underlying urinary tract abnormality
- enlarged prostate → obstruction
- can also lead to prostatitis & epidydimitis
- enlarged prostate → obstruction
What is E.coli colonization dependent on in UTIs?
- specific adhesions on the ends of long fimbriae (recognized by TLR4)
- P fimbriae
- Type 1 fimbriae
- motility
What is the normal mechanism of “transmission” of E.coli in UTIs?
- Not typically from person to person
- More often from organ to organ!
- women: anus → urethra
- up to 10x-50x more likely
- women: anus → urethra
What are nosocomial infections due to E.coli, K. pneumoniae, carbapenem-resistant Enterobacteriaceae (CRE), or vancomycin-resistant enterococci (VRE) associated with?
Urinary catheters
What three things are helpful to prevent UTIs?
- Regular urination
- Good hygiene
- Drink cranberry juice
- potentially blocks bacterial attachment to the epithelium
- Vaccines in clinical trial.
What two laboratory findings are diagnostic in Uncomplicated UTIs?
- 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
In complicated UTIs, colony counts (colony-forming units) can be much _______ for diagnosis?
LOWER
What does selective media contain?
- Compounds that selectively inhibit growth of some microbes, but not others.
What does differential media contain?
- An indicator (usually a dye)
- detects particular chemical reactions occurring during growth
What quick and easy test can you use to differentiate between Staph or Strep?
Catalase Test
- Catalase (+) = Staph
- Catalase (–) = Strep
How do you test for catalase activity?
- 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
- if catalase present → rapid release of oxygen bubbles
What test can you use to differentiate between Staph aureus vs. Staph saprophyticus?
- Coagulase test
- Staph aureus = coag +
- Staph saprophyticus = coag –
How do you test for coagulase activity?
- 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
If both bacteria are coagulase negative, how can you differentiate between Staph epidermidis or Staph saprophyticus?
- Novobiocin (drug) Sensitivity
- Staph epidermidies = sensitive
- ring indicates inhibition of growth
- Staph saprophyticus = resistant
- no ring/disturbance in bacterial growth
- Staph epidermidies = sensitive
When should you avoid treating with Nitrofurantoin?
- Suspected pyelonephritis
- due to poor upper urinary tract penetration
When should you use TMP-SMX to treat a UTI?
- 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
What are the recommended alternative treatments for UTI?
- Fluoroquinolones = Ciprofloxacin/Norfloxacin
- Amoxicillin/Clavulanate
When is it appropriate to treat a UTI with Fluoroquinolones?
(Hint: 4 reasons)
- 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
When is Amoxicillin/clavulanate a first line treatment for UTI?
UTI due to Staph saprophyticus
What UTI antibiotic treatment should NOT be used empirically?
Amoxicillin/clavulanate
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?
Yeast infection => due to Candida
What type of infection causes yellow, frothy discharge?
trichomoniasis
What color does beta-hemolysing bacteria turn blood agar?
Gold → complete hemolysis/digestion of RBC
(e.g. Staph aureus)
What color does alpha-hemolysing bacteria turn blood agar?
Green or brown → partical lysing of RBC
(e.g. Strep pneumoniae/viridans)
What color does gamma-hemolysing bacteria turn blood agar?
Pink → non-hemolytic
(e.g. Staph saprophyticus, Enterococcus)
What is MacConkey agar used for?
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
- utilize lactose => makes acid/lowers pH => pink colonies