Flashcards in Week 6: UTI ID Deck (52):
What type of bacteria cause most UTIs? What % of the time is it this type?
Normal enteric flora, 95%. Note: these are not the species that cause GI disease.
What is ABU?
Asymptomatic bacteriuria. UTI minus symptoms.
First line antimicrobials for uncomplicated UTI for men vs women
Men: Fluoroquinolone or TMP-SMX
Women: Nitrofurantoin or TMP-SMX
Therapy for complicated UTIs
Individualized, based on culture results
Natural barriers to harmful pathogens in urinary tract (4)
acidity of urine, act of urination -> desquamation, mucosal lining, urethral sphincter
What percent of UTIs occur by bacteria ascending the urethra? How do the rest occur?
90%. Rest are hematogenous.
What makes a UTI complicated?
underlying factors -> predisposed to ascending bacterial infection e.g. catheter, anatomic abnl, obstruction of urine flow, poor bladder emptying.
How do antibiotic and spermicide use make UTI more likely?
Change vaginal flora allowing for overgrowth of E. coli.
Pathogen most common for acute uncomplicated UTI. What percent of the time? How does it accomplish this?
E. coli 75%. Special attachment factors for transitional epithelium
____ is the #2 cause of uncomplicated UTI and accounts for ___%, more frequent in ________.
Staphylococcus saprophyticus, 5-15%, younger women
5-10% of uncomplicated UTIs caused by what other enteric organisms?
Klebsiella, Proteus, Enterococcus, Citrobacter.
Most common cause of complicated UTI
Other causes of complicated UTI
Aerobic and facultative anaerobic gram neg rods inc: Klebsiella, Proteus, Citrobacter, Acinetobacter, Morganella, and Pseudomonas. Gram Pos: enterococci and staph aureus. Yeasts. (prob don't need to know all these, just that there are many).
E. coli virulence factors contributing to UTI
Surviving low pH + surface adhesions. P fimbriae: hair-like protein interacting w renal epithelial cells, important in pyelonephritis and subsequent bloodstream invasion. Type 1 pilus (fimbria): all e. coli possess, not all express, mediate binding to uroplakins on bladder uroepithelial cells.
How does Sulfamethoxazole work?
Inhibits PABA to DHF via dihydropteroate synthetase
How does Trimethoprim work?
Inhibits conversion of DHF to THF via dihydrofolate reductase
How do the fluoroquinolones work?
Bind topo II/DNA gyrase --> tension -> double strand breaks
How does nitrofurantoin work?
Bacterial nitrofuran reductase reduces the drug -> damage or inactivate ribosomal proteins
How does urine chemistry block colonization? (3)
Acidity, lysozyme (breaks down peptidoglycan), lactoferrin (binds iron to prevent microorganisms from scavenging it)
How do the epithelial cells of the urinary tract prevent colonization?
Surface proteins differ from those of GI tract - prevents most enteric from gaining a foothold
What adaptive immune response defends the urinary tract?
Secretory IgA (requires previous exposure)
How does normal flora of the urinary tract prevent pathological colonization?
What are the 3 major threats to the urinary system?
Microorganisms moving from GI to urinary tract, catheters, immune system malfunction -> glomerulonephritis
Cause of urine cloudiness in UTI (2)
Bacteria and WBCs
Back pain with UTI symptoms suggests
Progression of infection to kidneys
Cause of orange-tinged urine
Pyridium or blood
Overall incidence of UTI in young women
0.5-0.7 episodes/year, recurring in 25-30%
Most common cause of nosocomial UTI
Catheter related (40%)
UTI in children suggests
Anatomic or functional abnormality
How many times more likely are UTIs in women than men
What does drinking cranberry juice help?
Blocks bacterial attachment to the epithelium
Lab findings for uncomplicated UTI (2)
Pyuria: 10+ neutrophils/ high power field
Bacteriuria >10^5 CFU/ mL urine
How may colony counts differ in complicated UTIs?
Can be much lower
What is selective media?
Contains compounds that selectively inhibit growth of some microbes but not others
What is differential media?
What is defined medium
What is undefined medium?
2 common microorganism culture tests
Catalase test, cytochrome oxidase test
How does the catalase test work?
Put a couple drops of hydrogen peroxide on bacteria. Bubbles = catalase pos, nothing = neg
Staph, enterococcus, and strep catalase and oxidase statuses
Staph: catalase pos
Strep: catalase neg
Entero: catalase neg
What test can differentiate staph aureus from saprophyticus?
Coagulase: pos with aureus, neg with other staph (saprophyticus and epidermidis
How does the coagulase test work?
Bacteria + fibrinogen = clumping? Pos: solid gelatin mass in test tube, neg test stays liquid.
What test can differentiate between epidermidis and saprophyticus?
Novobiocin sensitivity test
Novobiocin sensitivity/ resistance of epidermidis and saprophyticus
Epidermidis: sensitive. Saprophyticus: resistant
What does novobiocin do?
Inhibits DNA gyrase in susceptible micoorganisms
After taking antibiotics for a UTI, women are particularly susceptible to ____
Yeast, esp candida. This is an endogenous overgrowth.
What microscopic finding is suggestive of yeast?
Gram positive gamma hemolytic microorganism
Saprophyticus or enterococcus (sapro statistically more likely)