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Clinical Microbiology > Urinary tract infections > Flashcards

Urinary tract infections Flashcards

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1
Q

Anatomical structures of the urinary tract (5)

A
  1. Kidneys
  2. Ureters
  3. Bladder
  4. Urethra- commonly caused by STDs
  5. Prostate
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2
Q

Predisposition to urinary tract infections (5)

A
  1. Age- very young or very old
  2. Sex- sexually active females
  3. Underlying disease
  4. Medical devices- catheters
  5. Pregnancy- infection may be asymptomatic
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3
Q

Bacteriuria

A

Presence of uropathogenic bacteria in the urine

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4
Q

Cystitis

A

Inflammation of bladder. Causes 7 million office visits, >1 million hospitalizations. Hospital acquired, 20% of all hospitalized patients. One of the most common reasons why women present to the physician

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5
Q

Cystoscopy

A

Bilateral ureteral catheterization to determine location of
infection as in bladder, R-kidney or L-kidney. This procedure is very invasive

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6
Q

Dysuria

A

Pain or burning upon urination, presenting symptom of UTI

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7
Q

Nephrostomy

A

Surgical procedure leaving tubing directly in the kidney. The kidneys no longer empty into the bladder, urine leaves through the tube

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8
Q

Pyelonephritis

A

Acute infection of the kidney, renal pelvis associated with fever and flank pain due to inflammation of the kidney. Acute-symptomatic, Chronic-no pain. Can have an:
a. Ascending route
b. Descending route, hematogenous spread if untreated

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9
Q

Pyuria

A

Urine WBC count >10/HPF, important in establishing
presence of UTI.

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10
Q

Urethritis

A

Inflammation of the urethra, can be associated with
STD

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11
Q

Suprapubic aspirate

A

Urine collection by inserting needle directly into the bladder. Preferred for infants, if anaerobic infection is suspected, or collection of voided specimen is difficult. This sample is sterile. The procedure is very invasive but can be necessary if the infant has a very high fever or failure to thrive

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12
Q

Ascending

A

Moving from the bladder to the kidneys

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13
Q

Descending

A

Moving from the kidneys to the bladder

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14
Q

Straight catheter

A

Urine collection by inserting catheter through urethra into bladder. Considered an “in-and-out” procedure. Discard the first 15 to 30 mL and submit the next flow for the sample. An aseptic technique is essential, may require an iodine wash of the urethra

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15
Q

Indwelling catheter vs straight catheter

A

Permanent catheter used for individuals that may not be able to get to the bathroom, urine is collected from the port after cleaning. Cannot take a sample from the bag, it won’t be sterile. Treat like a clean-catch

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16
Q

Uncomplicated UTI

A

Infection of healthy women, no
structural or functional abnormalities. Dysuria is a common symptom. We look at colony counts to diagnose, looking for a single organism at >102 to >105 CFU/mL is significant. In catheterized patients and infants, low counts can be significant

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17
Q

Complicated UTI

A

Infection in patients with structural and/or functional abnormalities of the urinary tract. Can occur due to urinary obstruction or spinal cord injury, which predisposes them to infections. Also found in bladder cancer patients- the bladder has been removed and patients are at risk for kidney infections

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18
Q

Asymptomatic UTI

A

Infection with >105 CFU/ML
without symptoms. More common with pregnancy and the elderly. Leukocyte esterase can be negative

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18
Q

Urinalysis

A

Macroscopic - dipstick - Detects bacteria and WBC by nitrate reductase & leukocyte esterase.
b. Accutest - Detects bacteria and WBC by detecting catalase activity.
b. Microscopic – pyuria

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19
Q

Interpreting a urine dipstick

A
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20
Q

Automation

A

a. Microscopy –digital image capture
b. Dipstick – quantitative reading of strips. Strips themselves have NOT changed but evaluation of them has
c. MALDI-TOF MS – in development, poly-microbial infections problematic. 77% of catheter-associated UTI are poly microbic

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21
Q

Gram stain

A

if requested by physician
a. 10ul = 1 drop well-mixed unspun urine on slide.
b. 1 organism/oil field = >105 cfu/mL
c. 60-80% will be negative
d. ~50% of laboratories no longer perform

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22
Q

Symptoms of UTI- children less than 2 years old (2)

A

Nonspecific
1. Failure to thrive
2. Vomiting and fever

23
Q

Symptoms of UTI- children older than 2 years old (3)

A

Localized symptoms:
1. Dysuria
2. Increased frequency
3. Abdominal or flank pain

24
Q

Symptoms of UTI in adults- localized infection (2)

A

Lower UTI = cystitis
1. Dysuria, frequency, urgency
2. Occasional suprapubic tenderness

25
Q

Symptoms of UTI in adults- systemic infection (4)

A

Pyelonephritis:
1. Flank pain
2. Tenderness
3. Fever
4. Leukocytosis

26
Q

Acute glomerulonephritis (3)

A

Hypersensitivity disease. Symptoms:
1. Edematous eyes, fever, high blood pressure
2. Reddish brown urine
3. Red cell casts and protein in urine

27
Q

Clean-catch midstream specimen

A

First morning specimen recommended, collected by patient. Patients must cleanse genital area with soap and water. Void 20 mL, then collect urine into sterile container without stopping stream. Physician office laboratory (POL) uses a dip-slide urine culture container. Plate using 0.001 ml loop

28
Q

Indwelling catheter

A

Treated similar to clean-catch. Clean port with 70% alcohol; withdraw specimen with syringe, plate using 0.001 ml loop

29
Q

Straight catheter

A

More invasive. Single straight catheter: cleanse urethral opening with soap, rinse with sterile
water, discard initial urine flow. Plate using 0.001 ml loop

30
Q

Cystoscope specimen collection

A

Invasive specimen. Instrument for viewing and taking specimens from specific sites along the urinary tract. Plate using 0.01 ml loop

31
Q

Suprapubic urine aspirate

A

Invasive specimen that is never rejected, a physician signature is necessary. Prepare skin aseptically and anesthetize
c. Withdraw urine (~20 mL) directly into syringe through needle.
d. ONLY urine to be cultured anaerobically, if requested by physician.
e. Plate using 0.01 ml loop

32
Q

Which samples are unacceptable for culture? (4)

A
  1. Foley catheter TIPS – always contaminated with urethral flora. Tract above urethra - sterile
  2. 24 hr urines
  3. Catheter bag
  4. Bed pans
33
Q

Why are urines quantified?

A

To differentiate pathogens from contaminates. If there is a pathogen, there is a single organism (multiple bugs=rare), high colony forming units (CFU). Contaminates (commensals) – there are multiple types, low CFU

34
Q

Quantifying urine

A
  1. With 0.01 loop: (MORE invasive – plate MORE to increase recovery)
    #cfu/plate (found in 0.01 mL) x 100 = cfu/mL
  2. With 0.001 loop: (non-invasive specimen) #cfu/plate (found in 0.001 mL) x 1000 = cfu/mL
  3. Determine the relative importance of different organisms recovered from mixed infections
  4. Judge if organism is present as a contaminant or as the cause of infection
35
Q

When would a sample be considered to be contaminated?

A

> 2 enteric organism in amounts <104 cfu/mL suggests contamination- neither organism is predominant

36
Q

Situations when <105 cfu/mL is significant (2)

A
  1. If pyuria present in uncentrifuged urine - 8 PMN/mL is indicative of infection.
  2. 102 cfu/mL is considered significant: pregnancy, FUO, urinary tract obstruction, catheterized patients, follow up after catheter removal, follow up of previous therapy, infants, children, males, dilute urine
37
Q

Urine specimen processing

A

Refrigerate (4oC) immediately upon collection. Plate within 2 hr of collection. Store up to 24 hr if preservatives are used: boric acid, glycerol, or sodium formate

38
Q

Media for urine specimens (3)

A
  1. 5% sheep blood agar (SBA) or colistin-nalidixic acid agar (CNA)/phenylethyl alcohol agar (PEA)
  2. MacConkey agar or eosin methylene blue (EMB)
  3. If suprapubic aspirates or cystoscopy - CAP, tryptic soy broth or thioglycollate broth
39
Q

Urine plating

A

Urine should be well mixed before plating, choosing the correctly calibrated loop. The plates should only be incubated for 1 read (18 hour incubation only). 2nd read is only done if: less than 18hr incubation, straight catheter, suprapubic aspirate, pinpoint colonies, or gram doesn’t match culture results. All are incubated at 35oC.

40
Q

Special conditions when the physician suspects yeast

A

Sabouraud dextrose agar

41
Q

Special conditions when the physician suspects mycobacteria

A

decontaminate specialized medium

42
Q

Most commonly encountered urine pathogens (6)

A
  1. Gram-negative bacilli
  2. Staphylococcus - S. aureus & S. saprophyticus
  3. Yeast
  4. Beta-hemolytic Streptococcus
  5. Enterococcus
  6. G. vaginalis
43
Q

Presumptive (rapid) identification is acceptable for which organisms? (9)

A
  1. E. coli
  2. P. aeruginosa
  3. Yeast
  4. S. aureus
  5. Coagulase-negative Staphylococcus
  6. Enterococcus
  7. Viridans group Streptococci
  8. Lactobacillus spp.
  9. Corynebacterium spp.
44
Q

Which organism tends to cause ascending pyelonephritis?

A

E. coli

45
Q

Which organisms tend to cause descending pyelonephritis? (6)

A

Hematogenous spread
1. Staphylococcus aureus
2. Candida albicans and C. glabrata
3. Mycobacterium tuberculosis
4. Salmonella sp., early stages of enteric fever
5. Leptospira sp.
6. Proteus sp.

46
Q

Community acquired organisms causing cystitis (6)

A
  1. E. coli (80% of isolates)
  2. Klebsiella sp. & other Enterobacteriaceae
  3. Staphylococcus saprophyticus
  4. Streptococci: enterococci & group B streptococci
  5. Chlamydia sp. - not recovered by routine culture
  6. Pseudomonads
47
Q

Hospital acquired organisms causing cystitis (3)

A

20% of all hospitalized patients
1. E. coli, Klebsiella sp., Proteus mirabilis, Serratia marcescens and other Enterobacteriaceae
2. Pseudomonas aeruginosa
3. Enterococci

48
Q

Acute Urethral Syndrome

A

Symptoms- dysuria, frequency, urgency. Characterized by: <105 cfu/mL: >102 cfu/mL & pyuria. May be caused by any organism that causes cystitis, Chlamydia trachomatis, and Neisseria gonorrhoeae

49
Q

Other agents of UTI

A
  1. Mycoplasma hominis
  2. Ureaplasma urealyticum
  3. Gardnerella vaginalis- May represent vaginal contamination
  4. Viruses: adenovirus, HSV
50
Q

Diagnosis of cystitis vs. pyelonephritis

A

Invasive collection of specimens from specific sites (cystoscopy). WBC casts are found in pyelonephritis but NOT cystitis. Protein and RBCs are increased and bacteria are seen in pyelonephritis, but all of these factors are variable in cystitis. Patients are treated with a large dose of an antimicrobial drug. If successful, then the diagnosis is cystitis. If unsuccessful, then the infection is deep-seated pyelonephritis.

51
Q

WBC casts

A

Solidification of mucoprotein in the lumen of the kidney tubules; forms a mold or cast of the tubule trapping any material present. Casts can be hyaline (not pathogenic) or WBC (pathogenic)

52
Q

Hyaline casts

A

Not pathogenic, protein is Tamm-Horsefall. This protein is secreted by renal tubular epithelial cells and NOT from blood plasma.

53
Q

Empiric vs therapeutic treatment

A

The term “empiric therapy” refers to antibiotics that are administered during the period prior to the receipt of blood culture and antibiotic susceptibility test results, whereas the term “definitive therapy” refers to the antibiotic therapy given subsequent to receipt of these results

54
Q

Cystitis antimicrobial therapy

A

Consists of 7-10 days of oral antimicrobial therapy- 3 day course or single high dose. Commonly used oral agents include:
1. Trimethoprim (sulfamethoxazole) (SXT) = Bactrim, Septra
2. Cephalexin, 1st generation cephalosporin
3. Quinolones, e.g. naladixic acid, norfloxacin used for UTI only
4. Ampicillin, note: 25-35% E. coli are ampicillin-resistant

55
Q

Treatment of acute pyelonephritis

A

Inpatient - parenteral route (IV). Commonly used agents:
1. Trimethoprim (sulfamethoxazole (SXT)
2. Aminoglycosides
3. Broad spectrum beta-lactam agent

56
Q

Treatment of frequent re-infection

A

Treat long term with urinary antimicrobial agents-Sulfamethoxazole (SXT) and Nitrofurantoin (Furadantin) - used for UTI only

Clinical Microbiology (19 decks)

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