3.7.4. Urinary Tract Infections Flashcards
Describe complicated UTI’s
- serious infections
- often catheter related in hospital settings
- associated with metabolic disorders, secondary to anatomic or functional abnormalities that impair UT drainage or involve pathogens
- Often involve kidney stones
- Symptoms often non-specific
Describe uncomplicated UTI’s
- Sexual intercourse contributes to increased risk (as well as diaphragms and spermicides)
- Women at increased risk
- 10% of children acquire
Factors that can compromise a sterile urinary tract
- Bladder volume depletion
- sexual intercourse
- obstruction
- instrumentation/catheterization
- metabolic/ immunological state
Describe manifestations of cystitis
Cystitis is the introduction of pathogens via the bowel, vaginal flora, or catheter that involves:
- dysuria
- frequent urination
- Supropubic pain
- rule out STI if sexually active
Describe manifestations of pyelonephritis
Involves pathogen ascension from the bladder or hematogenous spread. Symptoms:
- flank pain
- fever
- nausea, vomiting, chills
- increased C reactive protein
- bacteremia (30% of cases)
describe uropathic E. Coli
- Enterobacteriaceae family
- normal intestinal flora
- facultatively anaerobic
- gram negative rods
- oxidase negative
virulence factors of E. coli
- type I fimbriae. These contribute to bladder colonization and exfoliation
- P pili. These adhere to digalactoside receptors which are important for kidney colonization
- Hemolysin. These damage cell membranes
- CNF toxin. These affect actin cytoskeleton by inhibiting rho GTPases
Describe staph saprophyticus
- gram positive cocci
2. adapted to urinary tract
describe proteus mirabilis
- contribute to biofilm formation
- belong to eneterobacteriaceae family
- swarming motility on agar
- produces urease which causes salt precipitation (relate to kidney stones)
- predilection for upper urinary tract
- Gram negative facultative anaerobe
lab criteria for positive urine culture of staph. saprophyticus
- gram positive cocci in clusters
- culture on blood agar
- Hemolytic: aureas
- non-hemolytic: other staph
- catalase positive
- coagulase negative: staph. epidermidis, staph. sapro.
- Novobiocin susceptibility: resistant = S. sapro.
urine culture uncomplicated UTA bacterial count
> 10E5 bacteria/ml single species
urine culture complicated UTA bacterial count
10E2-10E4 bacteria/ml
Effective oral therapy for most UTI
Trimethoprim. This inhibits bacterial dihydrofolate reductase which leads to bacterial stasis. (enterococci can incorporate dihydrofolate and tetrahydrofolate from urine increasing MIC by 60-357 fold)
What are common treatments for UTI?
- antibiotics (cephalosporin, timethroprim sulfate). Antibiotic resistance is common
- Phenazopyridine (pyridium) to relieve pain
risk factors for uncomplicated UTI
female (esp. sexually active), elderly, pregnant
risk factors for complicated UTI
metabolic disorders, kidney stones, catheter use
bacterial pathogen most often cause of uncomplicated UTI
E coli. can also be any of enterobacteriaceae family or staph. saprophyticus.
two types of colonization pili produced by UPEC (uropathogenic E. Coli)
- type 1: cause exfoliation of bladder cells to increase adherence. Important for bladder colonization
- P pili: adhere to digalactoside-receptors (P blood group). important for colonization of the kidney
common causes of complicated and catheter-related UTI
- biofilms on indwelling medical devices
2. invasive procedures
compare/contrast S. aureus, S. epidermidis, and S. saprophyticus for reservoir/key lab tests
S. aureus: coagulase positive
S. epidermidis/ S. saprophyticus: coagulase negative
S. saprophyticus: novobiocin resistant
lab characteristics of P. aeruginosa
gram negative rods, non-lactose fermenter on MacConkey agar, pyoverdin (green fluorescent spore) producer, oxidase positive
Why is P. aeruginosa such a successful nosocomial (hospital acquired) pathogen?
ubiquitous nature, resistance to detergent, resistant to antibiotics, forms biofilm, multiple colonization factors
What role does urease produced by P. mirabilis play in UTI?
causes precipitation of salts in solution and may contribute to formation of kidney stones and complicated UTI
How might lateral flagella (causes swarming in vitro) enable P. mirabilis to establish pyelonephritis?
They allow for swarming motility which allows for movement of organism up the urinary system
Discuss Enterococcus faecalis and E. faecium with regard to antibiotic resistance
Faecalis is susceptible to amoxicillin and nitrofurantoin. It has developed some resistance to these but is sensitive to linezolid.
How are UTI diagnosed in the laboratory? What is the importance of a “clean catch midstream” urine specimen?
Diagnosed by quantity in a specimen. Clean catch allows for clearance of perineum and for sampling the partially empty bladder, presumably a more accurate measurement.
