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Renal > Microbiology of UTI > Flashcards

Microbiology of UTI Flashcards

1
Q

What is a UTI?

A

Presence of micro-organisms in the urinary tract that are causing clinical infection

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2
Q

What is a lower UTI?

A

Infection confined to bladder (e.g cystitis)

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3
Q

What is an upper UTI?

A

Infection involving ureters +/- kidneys (e.g pyelonephritis)

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4
Q

What is a complicated UTI?

A

UTI complicated by systemic symptoms or urinary structural abnormalities/stones

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5
Q

What is bacteriuria?

A

Bacteria present in urine = doesn’t always mean infection, especially elderly or those with catheters

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6
Q

What is cystitis?

A

Inflammation of bladder = not always due to infection

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7
Q

What property does urine in the kidneys, ureters and bladder normally have?

A

Normally sterile

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8
Q

What is the lower urethra colonised by normally?

A

Coliforms and enterococci from the large bowel

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9
Q

What are some host factors that influence UTI occurrence?

A

Vaginal ecology, anatomy abnormalities, urinary retention, medical devices, familial tendency, frequent sex, uroepithelial cell susceptibility, high grade VUR, voiding dysfunction, spermicides

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10
Q

Why are UTIs more common in women?

A

Short wide urethra, proximity of urethra to anus, increased risk in pregnancy

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11
Q

What are the routes of infection?

A

Ascending infection or spread from blood stream

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12
Q

What are some features of the ascending infection route?

A

Common
Bacteria from perineal skin, bowel or lower urethra
Spreads from bladder up through ureters to kidneys

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13
Q

What are some features of the bloodstream rout of infection?

A

Rare
Bacteraemia or septicaemia seeded into kidneys
Multiple small abscesses and bacteria in urine

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14
Q

What are common UTI bacteria?

A

Aerobic bacilli

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15
Q

How are aerobic bacilli classified?

A

Lactulose fermenters = E.coli, klebsiella, enterobacter, serratia, cirobacter
Non-lactulose fermenters

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16
Q

How are non-lactulose fermenting aerobic bacilli classified?

A

Oxidase negative = morganella, proteus, providencia

Oxidase positive = pseudomonas aeruginosa

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17
Q

What are some features of proteus?

A 
Struvite stones (triple phosphate) = linked to urolithiasis
Foul smelling = burnt chocolate 
Swarming cultures of gram negative coliforms
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18
Q

What does proteus produce?

A

Urease = breaks down urea to form ammonia which increases urinary pH and causes salt precipitation

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19
Q

What are some features of pseudomonas aeruginosa?

A

Gram negative bacillus but not coliform
Associated with catheters/instrumentation
Resistant to most oral antibiotics apart from ciprofloxacin

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20
Q

How does ciprofloxacin work?

A

Inhibits bacterial DNA gyrase = prevents supercoiling of bacterial DNA

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21
Q

What patient groups is ciprofloxacin contra-indicated in?

A

Young children and pregnant women

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22
Q

What bacteria can ciprofloxacin be used to treat?

A

Only oral anti-pseudomonal antibiotic
Can treat almost all coliforms and some enterococci
Cant be used to treat staph. aureus or MRSA

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23
Q

What is the risk associated with ciprofloxacin?

A

Can cause C.diff

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24
Q

What are some gram positive causes of UTIs?

A

Enterococcus faecalis = hospital acquired infection
Staph saphrophyticus = women of child bearing age, coagulase negative
Staph aureus = rare, usually bacteraemia

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25
Q

What are the risk factors for cystitis?

A

Female, recurrent UTIs, sexual activity, vaginal infection, diabetes, obesity

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26
Q

What are the symptoms of cystitis?

A

Frequent and urgent urination, dysuria, suprapubic pain, nocturia, haematuria, malaise

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27
Q

What are the bacterial causes of cystitis?

A

UPEC, klebsiella pneumoniae, staph saprophyticus, enterococcus faecalis

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28
Q

What does UPEC stand for?

A

Uropathogenic E.coli

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29
Q

What are the UPEC virulence factors that lead to cystitis?

A

Adhesins = type 1 and chaperone-usher pilli
HlyA and CNF1 toxins
Aerobactin, enterobactin, yersiniabactin
Capsule

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30
Q

What are the risk factors for pyelonephritis?

A

Diabetes, HIV/AIDS, iatrogenic immunosuppression, urodynamic abnormalities

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31
Q

What are the symptoms of pyelonephritis?

A

Back and/or flank pain, fever, chills, malaise, nausea, vomiting, anorexia

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32
Q

What are the bacterial causes of pyelonephritis?

A

UPEC, klebsiella pneumoniae, staph aureus, enterococcus faecalis, proteus

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33
Q

What are the UPEC virulence factors that lead to pyelonephritis?

A

Adhesins = type 1 and P pilli
HlyA and CNF1 toxins
Aerobactin, Iha, TonB siderophore receptor
Flagella

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34
Q

What are the symptoms and signs of a UTI?

A

Dysuria, frequency, nocturia, haematuria

Fever, loin pain, rigors = suggest upper UTI

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35
Q

Why is a mid-flow sample of urine taken?

A

First urine passed is most likely to be contaminated

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36
Q

How do you collect a urine sample?

A

Label lab container
Wash perineum/urethral meatus with sterile saline
First urine passed into toilet
Without stopping collect next part of stream in bowl
Last urine passed into toilet
Transfer bowel contents into lab container

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37
Q

What are some specimen containers that can be used for urine samples?

A

Boricon container = contains boric acid to stop bacteria multiplying, works for 24hrs
Sterile universal container = must get to lab within 2hrs of collection

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38
Q

What are some alternative ways of taking a urine sample?

A

Clean catch urine = for children of patients with cognitive/physical restriction
Bag urine = for babies, often contaminated with bowel flora, negative result useful
Catheter specimen, suprapubic aspiration

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39
Q

What is the use of dipstick urine testing?

A

May indicate infection in select patients

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40
Q

What patients can dipstick urine tests not be used in?

A

Not suitable for elderly or catheter specimens

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41
Q

What does a positive leukocyte esterase on urine dipstick mean?

A

Indicates presence of white blood cells in the urine

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42
Q

What does a urine dipstick positive for nitrates mean?

A

Indicates presence of bacteria in urine

Some bacteria can reduce nitrates to nitrites = mainly coliforms

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43
Q

What bacteria do not test positive for nitrates on a urine dipstick?

A

Enterococcus, staph aureus and pseudomonas

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44
Q

What can dipstick urine tests be used to detect?

A

Protein and blood = not for infection diagnosis

45
Q

How are UTIs diagnosed in the lab?

A

Microscopy of urine = urgent cases, not routine, look for presence of polymorphs (pus cells), bacteria +/- RBC
Culture of urine = significant bacteriuria

46
Q

What is Kass’s criteria for bacteriuria?

A

> 10^5 organisms/ml = significant, probable UTI
<10^3 organisms/ml = not significant bacteriuria
10^4 organisms/ml = could be infection or contamination, repeat specimen

47
Q

What patients does Kass’s criteria apply to?

A

Women of child bearing age

48
Q

What kind of growth occurs in a UTI in a non-catheterised patient?

A

Genuine UTI in non-catheterised patient will usually be caused by a single organism = >10^5 org/ml of pure growth

49
Q

What does mixed growth usually signify?

A

Mixed growth of 2 or more organisms even if >10^5 orgs/ml is probably not significant = doesn’t apply to patients with abnormalities or urinary tract

50
Q

What are the features of the ideal antibiotic for treating an uncomplicated lower UTI?

A

Excreted in urine in high concentration, oral, inexpensive, few side effects

51
Q

How long does treatment of an uncomplicated UTI in a woman usually last for?

A

3 days

52
Q

Is anti-inflammatory treatment for cystitis sometimes as effective as anti-biotics?

A

Yes = in some patients

53
Q

What are the features of abacterial cystitis/urethral syndrome?

A

Patient has symptoms of UTI and pus cells in urine but no significant growth on culture

54
Q

What can cause abacterial cystitis/urethral syndrome?

A

May be due to early phase of UTI
Urethral trauma = honeymoon cystitis
Urethritis caused by gonorrhoea or chlamydia

55
Q

What can offer symptomatic relief in abacterial cystitis/urethral syndrome?

A

Alkanising urine

56
Q

What are the features of asymptomatic bacteriuria?

A

Significant bacteriuria but patient is asymptomatic = no pus cells in urine, incidental finding

57
Q

How is asymptomatic bacteriuria managed?

A

Antibiotic treatment usually not needed = especially in elderly, may recur even with antibiotic treatment

58
Q

How is asymptomatic bacteriuria managed in pregnancy?

A

All pregnant women screened at 1st antenatal visit

Usually treated with antibiotics

59
Q

What happens if asymptomatic bacteriuria is left untreated in a pregnant woman?

A

20-30% progress to pyelonephritis

May lead to intra-uterine growth retardation or premature labour

60
Q

What are some features of UTIs in patients with catheters?

A

Catheter-related UTI is one of most common causes of hospital acquired infection
The longer the catheter is in-situ the more likely it is to be contaminated with bacteria

61
Q

When should catheterised patients with significant growth be given antibiotics?

A

Only if there is supporting evidence of a UTI

62
Q

What do unnecessary antibiotics cause in catheterised patients?

A

Result in catheter being colonised with increasingly resistant organisms

63
Q

What is the antibiotic treatment for a lower UTI in a woman?

A

Nitrofurantoin or trimethoprim orally for 3 days

64
Q

What is the antibiotic treatment for a UTI in an uncatheterised male?

A

Get cultures = nitrofurantoin or trimethoprim orally for 7 days

65
Q

What is the antibiotic treatment for a complicated UTI or pyelonephritis in general practice?

A

Co-amoxiclav or co-trimoxazole for 14 days

66
Q

What is the antibiotic treatment for a complicated UTI or pyelonephritis in hospital?

A

Amoxicillin and gentamicin IV for 3 days

Co-trimoxazole and gentamicin IV if penicillin allergic

67
Q

What are the first line agents given in the Tayside formulary for treating coliforms?

A

Coliforms = gentamicin IV (first choice), amoxicillin (40%), trimethoprim (lower tract), co-trimoxazole (IVOST if sensitive)

68
Q

What are the first line agents given in the Tayside formulary for treating enterococci?

A

Amoxicillin IV (first choice), co-trimoxazole

69
Q

What are the antibiotics commonly used to treat UTIs?

A

1st line = amoxicillin, trimethoprim/co-trimoxazole, nitrofurantoin, gentamicin
2nd line = pivmecillinam, temocillin, cefalexin, co-amoxiclav, ciprofloxacin

70
Q

Why can gentamicin only be used in hospital?

A

Has to be given via IV

71
Q

Can gentamicin be used in pregnancy?

A

No

72
Q

What is the risk of the narrow therapeutic index of gentamicin?

A

Risk of toxicity and 8th nerve damage (deafness and balance problems) = only prescribe for 3 days unless advised otherwise

73
Q

How is gentamicin administered?

A

Given once daily = 7mg/kg (ideal body weight) then measure blood level 6-14 hrs later

74
Q

What organisms can gentamicin be used to treat?

A

Effective against most coliforms, pseudomonas and staph aureus (and MRSA)
Not active against enterococci

75
Q

What is gentamicin very effective at treating?

A

Severe gram negative (coliform related) sepsis

76
Q

What does ESBL stand for?

A

Extended spectrum beta lactamase

77
Q

What benefit does ESBL give to bacteria?

A

Makes them resistant to all cephalosporins and to almost all penicillins

78
Q

Where is the gene for ESBL carried in bacteria?

A

On a plasmid = often carries genes for other resistance too

79
Q

What are some antibiotics that may be useful against ESBL-producing bacteria?

A

Nitrofurantoin, pivmecillinam, fosfomycin, temocillin, meropenem, ertapenem

80
Q

What does CPE stand for?

A

Carbapenemase-producing enterobacteriaceae

81
Q

What are CPE?

A

Gram negative (coliform) bacilli that are resistant to meropenem = effectively resistant to all current antibiotics

82
Q

What mediates resistance of CPE?

A

Usually plasm-mediated and spreads very easily

83
Q

Where are some strains of CPE associated with?

A

The Indian sub-continent

84
Q

What are the second line agents given in the Tayside formulary for treating coliforms?

A

Aztreoriam, pivmecillinam, piperacillin/tazobactam, meropenem, quinolones, fosfomycin

85
Q

What are the second line agents given in the Tayside formulary for treating enterococci?

A

Vancomycin, linezolid, daptomycin, chloramphenicol

86
Q

What is the action of trimethoprim?

A

Inhibits bacterial folic acid synthesis = inhibits dihydrofolate reductase

87
Q

What are the benefits of trimethoprim?

A

Safe (avoid in first trimester), cheap, good concentration achieved in urine and prostate

88
Q

What is the other form trimethoprim can be given as?

A

Co-trimoxazole = risk of Steven-Johnson syndrome from sulphonamide

89
Q

What organisms is trimethoprim effective against?

A

Can be used to treat most coliforms and staph aureus (plus MRSA)
Not effective against pseudomonas

90
Q

What are some features of nitrofurantoin?

A

Cheap and narrow spectrum

Only useful in uncomplicated UTI = only reaches effective concentration in bladder

91
Q

When should use of nitrofurantoin be avoided?

A

Late pregnancy = can cause neonatal haemolysis

Breast feeding and children <3 months old

92
Q

What organisms is nitrofurantoin effective against?

A

Treats most coliforms, enterococci and staph aureus (plus MRSA)
Not effective against proteus or pseudomonas

93
Q

What are some features of amoxicillin?

A

Can be given orally or IV

Safe (even in pregnancy), high concentrations achieved in urine and very cost effective

94
Q

What organisms is amoxicillin effective against?

A

Treats enterococcus faecalis and some coliforms

>50% of E.coli strains are now resistant

95
Q

What is cefalexin?

A

1st generation oral cephalosporin = safe in pregnancy, good concentration in urine

96
Q

When is cefalexin used?

A

Only if organism is resistant to amoxicillin and trimethoprim = broad spectrum so may cause C.diff

97
Q

What does cefalexin carry a high risk of?

A

UTI recurrence post treatment

98
Q

What organisms is cefalexin effective against?

A

Treats coliforms and staph aureus

Not effective against MRSA, enterococci or pseudomonas

99
Q

What is pivmecillinam?

A

Esterified form of mecillinam = used for treating uncomplicated lower UTIs

100
Q

What are the benefits of pivmecillinam?

A

Effective against ESBL-producing coliforms = very beta-lactamase stable

101
Q

What are the negatives of pivemcillinam?

A

Not recommended in pregnancy

Not active against staph, strep, enterococci or pseudomonas

102
Q

What is co-amoxiclav?

A

Combination of amoxicillin and clavulanic acid = cheap, effective and safe in pregnancy, can cause C.diff

103
Q

What organisms is co-amoxiclav effective against?

A

Treats most coliforms, enterococci, and staph aureus

Not active against MRSA or pseudomonas

104
Q

What is temocillin?

A

Penicillin type antibiotic = active against ESBL-producing bacteria

105
Q

What is temocillin useful for?

A

Treating complicated UTI or urosepsis in patients whose renal function is too poor for gentamicin (not as effective as gentamicin however)

106
Q

What organisms does temocillin have no activity against?

A

Staph, strep, enterococci or pseudomonas

107
Q

What are carbapenems used for?

A

Reserve line antibiotics = active against ESBL producers

108
Q

What are some examples of carbapenems?

A

Meropenem
Ertapenem = doesn’t cover pseudomonas, given once a day OPAT use
Imipenem/imipenem-cilastatin = not used routinely

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