Microbiology of UTI Flashcards
What is a UTI?
Presence of micro-organisms in the urinary tract that are causing clinical infection
What is a lower UTI?
Infection confined to bladder (e.g cystitis)
What is an upper UTI?
Infection involving ureters +/- kidneys (e.g pyelonephritis)
What is a complicated UTI?
UTI complicated by systemic symptoms or urinary structural abnormalities/stones
What is bacteriuria?
Bacteria present in urine = doesn’t always mean infection, especially elderly or those with catheters
What is cystitis?
Inflammation of bladder = not always due to infection
What property does urine in the kidneys, ureters and bladder normally have?
Normally sterile
What is the lower urethra colonised by normally?
Coliforms and enterococci from the large bowel
What are some host factors that influence UTI occurrence?
Vaginal ecology, anatomy abnormalities, urinary retention, medical devices, familial tendency, frequent sex, uroepithelial cell susceptibility, high grade VUR, voiding dysfunction, spermicides
Why are UTIs more common in women?
Short wide urethra, proximity of urethra to anus, increased risk in pregnancy
What are the routes of infection?
Ascending infection or spread from blood stream
What are some features of the ascending infection route?
Common
Bacteria from perineal skin, bowel or lower urethra
Spreads from bladder up through ureters to kidneys
What are some features of the bloodstream rout of infection?
Rare
Bacteraemia or septicaemia seeded into kidneys
Multiple small abscesses and bacteria in urine
What are common UTI bacteria?
Aerobic bacilli
How are aerobic bacilli classified?
Lactulose fermenters = E.coli, klebsiella, enterobacter, serratia, cirobacter
Non-lactulose fermenters
How are non-lactulose fermenting aerobic bacilli classified?
Oxidase negative = morganella, proteus, providencia
Oxidase positive = pseudomonas aeruginosa
What are some features of proteus?
Struvite stones (triple phosphate) = linked to urolithiasis Foul smelling = burnt chocolate Swarming cultures of gram negative coliforms
What does proteus produce?
Urease = breaks down urea to form ammonia which increases urinary pH and causes salt precipitation
What are some features of pseudomonas aeruginosa?
Gram negative bacillus but not coliform
Associated with catheters/instrumentation
Resistant to most oral antibiotics apart from ciprofloxacin
How does ciprofloxacin work?
Inhibits bacterial DNA gyrase = prevents supercoiling of bacterial DNA
What patient groups is ciprofloxacin contra-indicated in?
Young children and pregnant women
What bacteria can ciprofloxacin be used to treat?
Only oral anti-pseudomonal antibiotic
Can treat almost all coliforms and some enterococci
Cant be used to treat staph. aureus or MRSA
What is the risk associated with ciprofloxacin?
Can cause C.diff
What are some gram positive causes of UTIs?
Enterococcus faecalis = hospital acquired infection
Staph saphrophyticus = women of child bearing age, coagulase negative
Staph aureus = rare, usually bacteraemia
What are the risk factors for cystitis?
Female, recurrent UTIs, sexual activity, vaginal infection, diabetes, obesity
What are the symptoms of cystitis?
Frequent and urgent urination, dysuria, suprapubic pain, nocturia, haematuria, malaise
What are the bacterial causes of cystitis?
UPEC, klebsiella pneumoniae, staph saprophyticus, enterococcus faecalis
What does UPEC stand for?
Uropathogenic E.coli
What are the UPEC virulence factors that lead to cystitis?
Adhesins = type 1 and chaperone-usher pilli
HlyA and CNF1 toxins
Aerobactin, enterobactin, yersiniabactin
Capsule
What are the risk factors for pyelonephritis?
Diabetes, HIV/AIDS, iatrogenic immunosuppression, urodynamic abnormalities
What are the symptoms of pyelonephritis?
Back and/or flank pain, fever, chills, malaise, nausea, vomiting, anorexia
What are the bacterial causes of pyelonephritis?
UPEC, klebsiella pneumoniae, staph aureus, enterococcus faecalis, proteus
What are the UPEC virulence factors that lead to pyelonephritis?
Adhesins = type 1 and P pilli
HlyA and CNF1 toxins
Aerobactin, Iha, TonB siderophore receptor
Flagella
What are the symptoms and signs of a UTI?
Dysuria, frequency, nocturia, haematuria
Fever, loin pain, rigors = suggest upper UTI
Why is a mid-flow sample of urine taken?
First urine passed is most likely to be contaminated
How do you collect a urine sample?
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
What are some specimen containers that can be used for urine samples?
Boricon container = contains boric acid to stop bacteria multiplying, works for 24hrs
Sterile universal container = must get to lab within 2hrs of collection
What are some alternative ways of taking a urine sample?
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
What is the use of dipstick urine testing?
May indicate infection in select patients
What patients can dipstick urine tests not be used in?
Not suitable for elderly or catheter specimens
What does a positive leukocyte esterase on urine dipstick mean?
Indicates presence of white blood cells in the urine
What does a urine dipstick positive for nitrates mean?
Indicates presence of bacteria in urine
Some bacteria can reduce nitrates to nitrites = mainly coliforms
What bacteria do not test positive for nitrates on a urine dipstick?
Enterococcus, staph aureus and pseudomonas
What can dipstick urine tests be used to detect?
Protein and blood = not for infection diagnosis
How are UTIs diagnosed in the lab?
Microscopy of urine = urgent cases, not routine, look for presence of polymorphs (pus cells), bacteria +/- RBC
Culture of urine = significant bacteriuria
What is Kass’s criteria for bacteriuria?
> 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
What patients does Kass’s criteria apply to?
Women of child bearing age
What kind of growth occurs in a UTI in a non-catheterised patient?
Genuine UTI in non-catheterised patient will usually be caused by a single organism = >10^5 org/ml of pure growth
What does mixed growth usually signify?
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
What are the features of the ideal antibiotic for treating an uncomplicated lower UTI?
Excreted in urine in high concentration, oral, inexpensive, few side effects
How long does treatment of an uncomplicated UTI in a woman usually last for?
3 days
Is anti-inflammatory treatment for cystitis sometimes as effective as anti-biotics?
Yes = in some patients
What are the features of abacterial cystitis/urethral syndrome?
Patient has symptoms of UTI and pus cells in urine but no significant growth on culture
What can cause abacterial cystitis/urethral syndrome?
May be due to early phase of UTI
Urethral trauma = honeymoon cystitis
Urethritis caused by gonorrhoea or chlamydia
What can offer symptomatic relief in abacterial cystitis/urethral syndrome?
Alkanising urine
What are the features of asymptomatic bacteriuria?
Significant bacteriuria but patient is asymptomatic = no pus cells in urine, incidental finding
How is asymptomatic bacteriuria managed?
Antibiotic treatment usually not needed = especially in elderly, may recur even with antibiotic treatment
How is asymptomatic bacteriuria managed in pregnancy?
All pregnant women screened at 1st antenatal visit
Usually treated with antibiotics
What happens if asymptomatic bacteriuria is left untreated in a pregnant woman?
20-30% progress to pyelonephritis
May lead to intra-uterine growth retardation or premature labour
What are some features of UTIs in patients with catheters?
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
When should catheterised patients with significant growth be given antibiotics?
Only if there is supporting evidence of a UTI
What do unnecessary antibiotics cause in catheterised patients?
Result in catheter being colonised with increasingly resistant organisms
What is the antibiotic treatment for a lower UTI in a woman?
Nitrofurantoin or trimethoprim orally for 3 days
What is the antibiotic treatment for a UTI in an uncatheterised male?
Get cultures = nitrofurantoin or trimethoprim orally for 7 days
What is the antibiotic treatment for a complicated UTI or pyelonephritis in general practice?
Co-amoxiclav or co-trimoxazole for 14 days
What is the antibiotic treatment for a complicated UTI or pyelonephritis in hospital?
Amoxicillin and gentamicin IV for 3 days
Co-trimoxazole and gentamicin IV if penicillin allergic
What are the first line agents given in the Tayside formulary for treating coliforms?
Coliforms = gentamicin IV (first choice), amoxicillin (40%), trimethoprim (lower tract), co-trimoxazole (IVOST if sensitive)
What are the first line agents given in the Tayside formulary for treating enterococci?
Amoxicillin IV (first choice), co-trimoxazole
What are the antibiotics commonly used to treat UTIs?
1st line = amoxicillin, trimethoprim/co-trimoxazole, nitrofurantoin, gentamicin
2nd line = pivmecillinam, temocillin, cefalexin, co-amoxiclav, ciprofloxacin
Why can gentamicin only be used in hospital?
Has to be given via IV
Can gentamicin be used in pregnancy?
No
What is the risk of the narrow therapeutic index of gentamicin?
Risk of toxicity and 8th nerve damage (deafness and balance problems) = only prescribe for 3 days unless advised otherwise
How is gentamicin administered?
Given once daily = 7mg/kg (ideal body weight) then measure blood level 6-14 hrs later
What organisms can gentamicin be used to treat?
Effective against most coliforms, pseudomonas and staph aureus (and MRSA)
Not active against enterococci
What is gentamicin very effective at treating?
Severe gram negative (coliform related) sepsis
What does ESBL stand for?
Extended spectrum beta lactamase
What benefit does ESBL give to bacteria?
Makes them resistant to all cephalosporins and to almost all penicillins
Where is the gene for ESBL carried in bacteria?
On a plasmid = often carries genes for other resistance too
What are some antibiotics that may be useful against ESBL-producing bacteria?
Nitrofurantoin, pivmecillinam, fosfomycin, temocillin, meropenem, ertapenem
What does CPE stand for?
Carbapenemase-producing enterobacteriaceae
What are CPE?
Gram negative (coliform) bacilli that are resistant to meropenem = effectively resistant to all current antibiotics
What mediates resistance of CPE?
Usually plasm-mediated and spreads very easily
Where are some strains of CPE associated with?
The Indian sub-continent
What are the second line agents given in the Tayside formulary for treating coliforms?
Aztreoriam, pivmecillinam, piperacillin/tazobactam, meropenem, quinolones, fosfomycin
What are the second line agents given in the Tayside formulary for treating enterococci?
Vancomycin, linezolid, daptomycin, chloramphenicol
What is the action of trimethoprim?
Inhibits bacterial folic acid synthesis = inhibits dihydrofolate reductase
What are the benefits of trimethoprim?
Safe (avoid in first trimester), cheap, good concentration achieved in urine and prostate
What is the other form trimethoprim can be given as?
Co-trimoxazole = risk of Steven-Johnson syndrome from sulphonamide
What organisms is trimethoprim effective against?
Can be used to treat most coliforms and staph aureus (plus MRSA)
Not effective against pseudomonas
What are some features of nitrofurantoin?
Cheap and narrow spectrum
Only useful in uncomplicated UTI = only reaches effective concentration in bladder
When should use of nitrofurantoin be avoided?
Late pregnancy = can cause neonatal haemolysis
Breast feeding and children <3 months old
What organisms is nitrofurantoin effective against?
Treats most coliforms, enterococci and staph aureus (plus MRSA)
Not effective against proteus or pseudomonas
What are some features of amoxicillin?
Can be given orally or IV
Safe (even in pregnancy), high concentrations achieved in urine and very cost effective
What organisms is amoxicillin effective against?
Treats enterococcus faecalis and some coliforms
>50% of E.coli strains are now resistant
What is cefalexin?
1st generation oral cephalosporin = safe in pregnancy, good concentration in urine
When is cefalexin used?
Only if organism is resistant to amoxicillin and trimethoprim = broad spectrum so may cause C.diff
What does cefalexin carry a high risk of?
UTI recurrence post treatment
What organisms is cefalexin effective against?
Treats coliforms and staph aureus
Not effective against MRSA, enterococci or pseudomonas
What is pivmecillinam?
Esterified form of mecillinam = used for treating uncomplicated lower UTIs
What are the benefits of pivmecillinam?
Effective against ESBL-producing coliforms = very beta-lactamase stable
What are the negatives of pivemcillinam?
Not recommended in pregnancy
Not active against staph, strep, enterococci or pseudomonas
What is co-amoxiclav?
Combination of amoxicillin and clavulanic acid = cheap, effective and safe in pregnancy, can cause C.diff
What organisms is co-amoxiclav effective against?
Treats most coliforms, enterococci, and staph aureus
Not active against MRSA or pseudomonas
What is temocillin?
Penicillin type antibiotic = active against ESBL-producing bacteria
What is temocillin useful for?
Treating complicated UTI or urosepsis in patients whose renal function is too poor for gentamicin (not as effective as gentamicin however)
What organisms does temocillin have no activity against?
Staph, strep, enterococci or pseudomonas
What are carbapenems used for?
Reserve line antibiotics = active against ESBL producers
What are some examples of carbapenems?
Meropenem
Ertapenem = doesn’t cover pseudomonas, given once a day OPAT use
Imipenem/imipenem-cilastatin = not used routinely
