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MIC3041 Medical Microbiology > Urinary Tract Infections > Flashcards

Urinary Tract Infections Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Define bacteriuria

A

Presence of bacteria in urine

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2
Q

Define cystitis

A

Infection in the bladder

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3
Q

Define dysuria

A

painful urination

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4
Q

Define hematogenous

A

arising/spreading in the blood

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5
Q

Define hypertrophy

A

abnormal enlargement of an organ

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6
Q

Define MSU

A

mid-stream urine

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7
Q

Define pyuria

A

presence of white blood cells/pus in urine

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8
Q

Define pyelonephritis

A

infection in the kidney

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9
Q

Define siderophore

A

low MW compounds secreted by bacteria that bind iron

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10
Q

Define SPA

A

suprapubic aspiration (urine sample from the bladder)

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11
Q

Define UPEC

A

uropathogenic E. coli

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12
Q

What are the 5 parts of the urinary tract?

A 
Kidney
Ureters
Bladder
Urethra
Prostate
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13
Q

What is the function of the kidneys?

A

Filter metabolites and other materials including some drugs from the blood

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14
Q

What is the function of the ureters?

A

Lead urine from kidneys to the bladder

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15
Q

What is the function of the bladder?

A

Storage point for urine

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16
Q

What type of metabolism is urea from?

A

Protein metabolism

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17
Q

What type of metabolism is uric acid from?

A

Nucleic acid metabolism

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18
Q

What type of cells line the mucosa of the ureters and bladder?

A

Transitional/Stratified epithelium - urothelium

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19
Q

What can the urothelium produce?

A

Cytokines, chemokines and secretory IgA

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20
Q

How many urinary tract infections occur around the world annually?

A

130-175 million

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21
Q

What do UTIs usually result from?

A

Bacterial infection of the ascending urethra

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22
Q

What percentage of women have recurring UTIs?

A

20-30%

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23
Q

What age group of men typically get UTIs?

A

Men over 50

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24
Q

What is the epidemiology of UTIs?

A

Can be either community-acquired or nosocomially-acquired (hospitals, mostly from catheterisation)

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25
Q

What are the symptoms of a lower UTI?

A 
Urethra (urethritis):
- frequency of passing urine
- burning sensation (dysuria)
- urgency
Bladder (cystitis):
- above symptoms and pain and fever
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26
Q

What are the symptoms of an upper UTI?

A

Kidney (pyelonephritis):

  • similar symptoms to lower UTIs
  • fever, renal tenderness
  • sometimes nausea, vomiting, diarrhoea or constipation
  • loin pain
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27
Q

Who gets UTIs?

A

Infants M>F
Children, adolescents m=F
Adults F»M

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28
Q

What is the frequency of UTIs in women?

A

6% of women/year get UTIs

Most women at least once

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29
Q

What is the frequency of UTIs in men?

A

Uncommon in men with normal urinary tracts

More common in elderly men with impaired flow

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30
Q

What are predisposing factors for a UTI?

A
  • Inoculation of organisms into urethra
  • Disruption of normal urine flow
  • Incomplete bladder emptying
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31
Q

What are some causes of inoculation of organisms into the urethra?

A
  • direct environment contamination
  • Catheterisation
  • Trauma/surgery
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32
Q

What are some causes of disruption of normal urine flow?

A
  • anatomical abnormalities
  • enlargement of prostate
  • kidney stones (calculi)
  • tumours
  • pregnancy
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33
Q

What are some causes of incomplete bladder emptying?

A
  • loss of normal neurological function associated with spina bifida, multiple sclerosis, paraplegia
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34
Q

Which organisms are involved in the acquisition of a UTI through the ascending route and their percentage?

A 
E. coli (mainly O and K serotypes) 80%
Staphylococcus spp. (saprophyticus, normal vaginal microbiota) 10%
Proteus spp. (mirabilis) 5%
Other Gram-negative 4%
Other Gram-positive 3%
35
Q

What are the O and K serotypes of E. coli?

A 
O = LPS type
K = capsule type
36
Q

What enzyme does Proteus mirabilis express?

A

It expresses urease, which breaks down urea into ammonia. Ammonia increases the pH, causing precipitation of things such as calcium carbonate which can cause stones and disrupt flow

37
Q

Do viruses typically cause UTIs?

A

Whilst they can be recovered from urine they rarely cause symptoms

38
Q

Which viruses cause UTI symptoms?

A

Adenovirus
- may cause haemorrhagic cystitis
Polyomaviruses
- initially infect respiratory tract then moves to kidneys and ureter cells (35-50%)
- reactivate during pregnancy and immune compromise (haemorrhagic cystitis)
HIV and mumps may infect kidneys

39
Q

Which viruses can be shed asymptomatically in infants?

A

Cytomegaloviruses and rubella

40
Q

What fungal species can cause UTIs?

A

Candida spp.

41
Q

What protozoa can cause UTIs?

A

Trichomonas vaginalis

- causes vaginitis

42
Q

What parasite can cause UTIs?

A

Schistosoma haemotobium

  • eggs may penetrate the bladder wall
  • can lead to hematuria and ureter obstruction
43
Q

What are the 10 steps in the Schistosoma haemotobium lifecycle?

A
  1. Egg excreted out along the urine
  2. Eggs hatch, releasing miracidia
  3. Miracidia penetrate snail tissue
  4. Sporocyst in snail with developing cercariae
  5. Cercariae released from snail and actively swim in water
  6. Human skin penetration
  7. Cercariae lose tails and become schistosomulae
  8. Circulation
  9. Migrate to portal blood in liver and mature
  10. Paired adult fluke migrate to venous plexus bladder
    REPEAT
44
Q

What is the infective stage of the Schistosoma haemotobium lifecycle?

A

Step 5: Cercariae released from snail and actively swim in water
Step 6: Skin penetration

45
Q

What is the diagnostic stage of the Schistomsoma haemotobium lifecycle?

A

Step 1: Egg excreted out along the urine

46
Q

Define hematogenous spread

A

Originating in the blood or spread through the bloodstream.

47
Q

What are 3 pathogens that cause hematogenous spread to cause a UTI?

A

Mycobacterium tuberculosis
Salmonella typhi
Staphylococcus aureus

48
Q

Which organisms are involved in the acquisition of a UTI through nosocomial means and their percentage?

A 
E. coli & Proteus mirabilis 45%
Enterobacter & Klebsiella 11%
Other Gram-negatives (Pseudomonas) 25%
Other Gram-positives (Enterococcus) 14%
Candida spp. 5%
49
Q

Why is the list and percentages of ascending route and nosocomial causes different?

A

Because they have a different set of virulence factors as they don’t need as many due to many being able to infect through medical devices such as catheters, where they don’t have to fight against host immune factors to gain entry

50
Q

What is the antibiotic resistance level like for nosocomial infections?

A

Most are antibiotic resistant

51
Q

What is the most common UTI pathogen?

A

Uropathogenic E. coli

52
Q

What is the main virulence factor of UTI pathogens?

A

The ability to adhere to urothelium

53
Q

What are 3 host defence mechanisms against UTIs?

A
  • Main defence is urinary flushing
  • Also antibacterial molecules and antibodies
  • Low free iron
54
Q

What are 5 virulence mechanisms of UPEC?

A
  1. Colonisation/adherence through Fim and Pap pili
  2. Flagella to allow ascension to kidneys
  3. Scavenge iron through siderophores
  4. Express toxins, Hly haemolysin
  5. Ability to form a biofilm
55
Q

What is the mode of action of colonisation/adherence in UPEC?

A

They have Fim and Pap pili that allow binding to urothelium

Adherence to urothelium cells facilitates entry

56
Q

What is the mode of action of scavenging iron in UPEC?

A

They secrete siderophores which steal iron from host molecules

57
Q

What is the mode of action of toxins in UPEC?

A

They secrete Hly haemolysin which is associated with increased UTI severity
It may be involved in lysis of host cells for nutrient acquisition or for modification of host responses

58
Q

What is the mode of action of biofilm formation in UPEC?

A

It enables it to be quiescent and hidden from the immune system

59
Q

What siderophore does UPEC have?

A

Enterobactin

60
Q

What host defence interacts with enterobactin?

A

Lipocalin which is a protein that can bind to enterobactin and inactivate it

61
Q

How does UPEC overcome lipocalin?

A

They sometimes express another siderophore called salmochelin which cannot be bound by lipocalin and is therefore still functional to steal iron.

62
Q

What are the 6 steps in UPEC bacterial/host interaction?

A
  1. UPEC with pili adhere
  2. UPEC secretes toxins
  3. Siderophores are activated to steal iron
  4. UPEC invades bladder cells
  5. UPEC multiples and escapes the bladder cells
  6. Host defences
63
Q

What is the main diagnostic for UTI and why?

A

The main diagnostic for UTIs is significant numbers of bacteria in the urine.
This is because urine is normally sterile, however, distal urethra and surrounding skin has commensal and contaminating organisms

64
Q

What is the problem with using urine as a diagnostic measure and how do we overcome it?

A

The problem is how do we get an uncontaminated sample.
The answer is taking care in gaining a sample and using a quantitative culture to distinguish between contamination and infection

65
Q

How is urine collected from adults?

A

Collect a mid-stream urine (MSU) sample

  1. Cleanse genital area
  2. Void first part of urine (helps to remove lower urethra contaminants)
  3. usually cleanse again
  4. sample MSU in sterile container
66
Q

What sampling method is used for infants?

A

Clean catch bag specimen. Plastic bag stuck to penis or perineum
Often highly contaminated with faecal material

67
Q

What sampling method is used for patients with catheters?

A

Sample directly from the catheter tube (not sample that has been in drainage bag)
Low contamination

68
Q

What is the sampling method with no contamination?

A

Suprapubic aspiration
Sample directly from the bladder by needle collection
Generally used for infants and elderly

69
Q

How should urine samples be transported and why?

A

Should be transported ASAP and stored at 4 degrees celsius until processing
This is because although urine is normally sterile it is a rich growth medium for many organisms. And since quantitative culture is usually required for diagnosis, extra growth needs to be avoided as it will distort original sample numbers.

70
Q

How is the urine sample investigated in the lab and what are they looking for?

A

It undergoes microscopic examination.

  • organisms may be observable if in large numbers
  • assess quality of the specimen
  • WBC count (<10/microlitres, normal)
  • RBC count (<10/microlitres, normal)
  • Renal casts (indicate renal tubule damage)
  • Crystals
71
Q

What do renal casts indicate?

A

Renal tubule damage, due to precipitated protein and cells

72
Q

What do crystals in the urine indicate?

A

pH changes or low flow

73
Q

What is examined in a wet preparation?

A

Casts and crystals

74
Q

What is the Tamm-Horstall protein indicative of?

A

pH change

75
Q

What are the steps in the laboratory investigation of a urine sample?

A
  1. Centrifuge urine
  2. Gram-stain for bacteria
  3. Acid-fast stain if M. tuberculosis is suspected
  4. Quantitative culture at 37 degrees for 24 hours on both HBA and MacConkey agar (selective for Gram-negative)
  5. Surface viable count: spread 0.1ml of 1/100 diluted urine (100 CFU = 10^5 CFU/ml urine)
  6. Test for antibiotic sensitivity
76
Q

What is involved in a dipslide?

A

Dipslide with both HBA and MAC
Culture 18-24 hours at 37 degrees in O2
Colony counts calculated by reference standards

77
Q

What is the interpretation of MSU samples?

A

<10^3 CFU is normal contamination
10^3 - 10^5 unclear diagnosis; bad sample?
>10^5 CFU reliable indicator of infection

Catheter samples (<100 CFU/ml = infection)
SPA any CFU/ml = infection
78
Q

Why do some patients with UTI symptoms have no growth on culture?

A 
Fastidious/unusual organisms
- Haemophilus spp., M. tuberculosis
Recent antibacterial therapy
- was therapy begun prior to taking sample
Not a bacterial infection
- may be an STI
- viral infection
79
Q

How do we treat uncomplicated lower UTIs?

A

Can be treated with oral antibiotics which are

  • active against pathogen
  • excreted in active form into urine
  • active at urinary pH
  • adequate concentration in the urine
80
Q

What are the best guess antibiotics used for uncomplicated lower UTIs?

A

Cephalosporins, nitrofuratoin

Sulfametoxazol-trimethoprim (emerging resistance)

81
Q

How do we treat pyelonephritis?

A

Systemic antibiotic followed by oral antibiotic

82
Q

How do we treat infections cause by hematogenous spread?

A

They require specific antibiotic therapy

83
Q

How do we treat nosocomial infections?

A

They first need to be tested for antibiotic sensitivity as they are highly likely to be resistant to some antibiotics

MIC3041 Medical Microbiology (11 decks)

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