Microbiology 10 - Urinary Tract Infections Flashcards
Which organism is the most common cause of UTI?
E coli (only certain serotypes eg, O1,O2,O4- due to virulence factors, e.g p.fimbrae that help to adhere and ascend epithelium)
What are the symptoms of UTI in babies?
Vomiting and failure to thrive
What are the symptoms of pyelonephritis?
Fever, rigors, flank pain and urinary symptoms
What are squamous epithlial cells in a MSU indicative of?
Contamination
For how long should antibiotics be taken in uncomplicated UTI?
3 days
7 days in males, upper uti in females
What is the most common route of infection for candida UTIs?
Urinary catheters
What is the empirical antibiotic treatment for pyelonephritis?
Co-amoxiclav +/- gentamycin
Main few causes of UTI
Ecoli 01,02,04
Proteus mirabilis
o Proteus is usually the organism associated with kidney stones
o Tends to occur in abnormal urinary tracts
- Staphylococcus saprophyticus (coag neg)
o This is the 2nd commonest cause of UTI in young women - Klebsiella aerogenes
o Infection tends to occur in abnormal urinary tracts (i.e. stones, neurological or anatomical abnormalities) - Enterococcus faecalis
- Staphylococcus epidermidis (coag neg)
o Can cause UTI in the presence of prosthesis (e.g. procedures or long-term indwelling catheter)
What does presence of staph aureus in urine suggest
Most likely due to haematogenous spread
o Should be CONCERNED about ENDOCARDITIS + EMBOLI or BACTERAEMIA
o Thus, you should take blood cultures if S. aureus is found to make sure there is no haematogenous spread
Staph aureus does not cause ascending infection as it lacks virulence factors to ascend urinary epithelium, thus it is likely via haematogenous spread. Can cause renal abscesses
Urine dip interpretation
Nitrites++ - most likely UTI
Nitrites -ve but WBC ++ - this MIGHT be UTI
Blood ++ and protein ++ but nitrites and WBCs -ve - consider alternative diagnose E.g. stones
Everything -ve - it is unlikely to be UTI
How are nitrites found in urine produced
Nitrites are very specific because they are produced by E. coli
o E coli have enzymes which allow nitrates to be reduced to nitrites
o So, +ve nitrites is suggestive of coliforms being present in the urine
Nitrite-negative and leukocyte-positive may be a UTI caused by a non-coliform bacterium
What is leukocyte esterase?
Leukocyte esterase is produced by the leukocytes- this is a marker of inflammation
When is asymptomatic bacteriuria a cause for concern
Pregnant women
Kids
Men
In elderly it is not a cause for concern unless they are symptomatic
What is the cut-off for WCC and cfu to diagnose UTI
WCC > 10^4 (AKA pyuria-white blood cells in urine)
cfu > 10^5
In young kids, pyuria may be absent so correlate with clinical symptoms
If there is sterile pyuria, think about other causes eg. chlamydia, TB, renal abnormalities. Antibiotic use can also cause sterile pyuria.
What agar is used for urinalysis
Chromogenic agar
Pink= E. coli
Blue= Klebsiella, Enterobacter
Light turquoise= Enterococcus (gram positive organisms
