Microbiology Flashcards
Where are bacteria found in the normal urinary tract?
Kidneys, ureter and bladder - sterile
Urine colonised at lower urethra
What is the definition of a urinary tract infection?
The presence of micro-organisms in the urinary tract that are causing clinical infection
What is the definition of a complicated UTI?
UTI complicated by systemic sepsis or urinary structural abnormality or stones
What is cystitis?
Inflammation of the bladder
What factors increase the risk of developing UTI?
Female
Catheterised patient
Patients with abnormalities of the urinary tract
What are the two routes of infection for UTI?
Ascending infection (from urethra towards kidneys)
Bloodstream
Which bacteria is associated with UTI and development of stones?
Proteus sp. (coliform)
What are the causal organisms of UTI?
E. Coli
Klebsiella sp.
Enterobacter sp.
Enterococcus
Proteus sp. and other coliforms
Staphlycoccus
Pseudomonas aueruginosa
Why is proteus sp associated with formation of stones?
Produces urease which breaks down urea to form ammonia, which increases urinary pH - precipitation of salts and foul smelling urine
Which bacteria usually causes UTI in women of child bearing age?
Staphylococcus saphrophyticus: a type of coagulase negative staph.
What is the difficulty in prescribing oral antibiotics to treat UTI with pseudomonas aeruginosa?
Resistant to most oral antibiotic except ciprofloxacin which can cause C. difficile infection
What bacteria is associated with UTI in catheterized patients and those with UT instrumentation?
Pseudomonas aeruginosa
What are the symptoms of UTI?
Dysuria
Frequency
Nocturia
Haematuria
Fever
Rigors
Loin pain
Which symptoms imply upper UTI?
Loin pain
Fever
Rigors
Why is it important to get a mid stream sample of urine from a patient with suspected UTI?
First passed urine will be contaminated with organisms from urethra
What is the advantage of using a red lidded container to transport urine specimen to the lab?
Boric acid topped will keep urine sterile for up to 24 hours i.e. will not allow bacterial overgrowth
Which substance indicates the presence of leukocytes/white blood cells in the urine?
Leukocyte esterase
What does the presence of nitrites in the urine indicate?
Presence of bacteria in the urine
Which bacteria do not test positive for nitrites in urine?
Enterococcus spp.
Why might culture of urine be done?
To test for significance of bacterial growth in urine
What on urine culture would indicate significant bacterial growth?
>300 colonies present
>10^5 organism/ml present
Is a mixed growth i.e. two or more organisms with >10^5 organisms per ml significant?
Probably not
What is the significance of an ESBL-producing bacteria?
ESBL = extended spectrum beta-lactamase
Makes bacteria resistant to ALL cephalosporins and to almost all penicillins
Which antibiotics may be useful against ESBL-producing bacteria?
Nitrofurantoin (oral)
Pivmecillinam (oral)
Fosfomycin (oral)
Temocillin (IV)
Meropenem (IV)
Ertapenem (IV)
What is carbapenemase-producing enterobacteriaceae (CPE)?
Gram negative (coliform) bacilli that are resistant to meropenem - this usually means that they are effectively resistant to ALL current antibiotics
What length of course is usually sufficient to treat an uncomplicated lower UTI in women?
3 days
What first line antibiotics are used for UTI?
Amoxicillin (IV, oral)
Trimethoprim (oral, but can be given IV as cotrimoxazole)
Nitrofurantoin (oral)
Gentamicin (IV)
What are the second line antibiotics for UTI?
Pivmecillinam (oral)
Temocillin (IV)
Cefalexin (oral)
Co-amoxiclav (IV, oral)
Ciprofloxacin (IV, oral)
What UTI organisms does amoxicillin treat?
Enterococcus faecalis
Some coliforms, but >50% E. coli now resistant, and many other coliforms also resistant
When should use of trimethoprim be avoided?
1st trimester of pregnancy
What is co-trimoxazole?
A combination of sulphamethoxazole and trimethoprim
What UTI organisms does trimethoprim have effect against?
Most coliforms
Staph aureus incl. MRSA
NOT Pseudomonas sp.
Why is nitrofurantoin only useful in uncomplicated lower UTI?
Only reaches effective concentrations in bladder urine
When should use of nitrofurantoin be avoided and why?
Late pregnancy, can cause neonatal haemolysis
Breast feeding
Children <3 months old
What organisms does nitrofurantoin have effect against?
Most coliforms
Enterococci
Staph aureus incl MRSA
NOT proteus sp and pseudomonas sp
What organisms does gentamicin have effect against?
Most coliforms
Pseudomonas sp
Staph aureus incl MRSA
NOT enterococci
When is gentamicin use in UTI particularly useful?
Very effective drug in severe Gram negative (coliform-related) sepsis
How long should gentamicin be prescribed for?
3 days only
When is pevmicillam useful in treating UTI?
Useful for treating lower uncomplicated UTI
Very beta-lactamase stable – has activity against very antibiotic-resistant coliforms that produce extended spectrum beta-lactamases (ESBLs)
Is pevmicillam use recommended in pregnancy?
No
When is temocillin useful in treating UTI?
Very beta-lactamase stable – has activity against very antibiotic-resistant coliforms that produce extended spectrum beta-lactamases (ESBLs)
Useful for treating complicated UTI/urosepsis in patients whose renal function is too poor for gentamicin, but is NOT as effective as gentamicin clinically
What empirical antibiotic treatment is issued for lower UTI in women?
Trimethoprim or nitrofurantoin orally (3 days)
What empirical antibiotic is useful for treating uncatheterised male UTI?
Trimethoprim or nitrofurantoin orally (7 days)
What empirical antibiotic in a GP setting is useful for treating complicated UTI or pyelonephritis?
Co-amoxiclav or co-trimoxazole (14 days)
What empirical antibiotic treatment in a hospital setting is given to treat complicated UTI or pyelonephritis?
Amoxicillin and gentamicin IV for 3 days (cotrimoxazole and gentamicin if penicillin allergy), stepdown as guided by antibiotic sensitivities
When should asymptomatic bacteuria always be treated?
Pregnancy
What complications may arise from untreated asymptomatic bacteuria in pregnancy?
20-30% progress to pyelonephritis
May lead to intra-uterine growth retardation (IUGR) or premature labour
What may be the cause of abacterial cystitis?
May be an early phase of UTI
May be due to urethral trauma - “honeymoon cystitis”
May be due to urethritis caused by chlamydia, gonorrhoea
How might symptoms of abacterial cystitis be helped?
Alkalanising the urine
Why should antibiotics only be given to catheterised patients displaying symptoms of UTI?
Giving too many antibiotics will only colonise catheter with increasingly resistant organisms
