UTIs Flashcards
Infections of the urinary tract
One of the commonest bacterial infections
Up to 30% of women have recurrent UTI episodes
Any pathogen has to overcome the normal defenses in the Urinary tract
Main defence against UTIs
Flushing by urine
Route of infection (DIAGRAM)
Infection usually ascends from the external site up the UT continuum
This can in some cases also lead to involvement of the kidneys
Catheterisation a common route of infection
The female urinogenital tract is particularly vulnerable to infection with fecal bacteria, mainly because the urethra is shorter and nearer to the anus.
But also due to the nature of intercourse…..
Definitions of urethritis
Inflammation of urethra
Definition cystitis
Inflammation of bladder
Definition of dysuria
Painful urination
Pyuria
Urine that contains pus
Pyelonephritis
Kidney infection, characterised by fever and back pain
Host factors - urinary tract (DIAGRAM)
Renal calculi Ureteric reflex Tumours in and adjacent to urinary tract Pregnancy, bladder stones Neurological problems: -incomplete bladder empying -large vol of residual urine -loss of sphincter control Prostatic hypertrophy Short urethra in women Catherization
Bacterial attributes in urinary tract (pathogen factors)
DIAGRAM
Capsular antigens Hemolysins Urease Adhesion to uroepithelium (e.g. P. fimbriae in E.coli) Introital colonization
Diagnosis of UTIs: steps
Sampling of midstream Urine (with care) -cloudy or clear -haematuria? (urine might be pink) -culture on agar plates > 2x105 cells/ml -traces of protein, leukocytes >10/ml - > nitrites (NO3- > NO2-) Pure or mixed growth? Gram Stain of isolated bacteria or direct staining from urine sample
Main culprits: community UTIs
E.coli - gram negative rod -80% Proteus mirabilis -gram negative pleomorphic rod -swarming motility Staphylococcus saprophyticus -gram positive coccus -particularly common in young women of sexually active age
Main culprits: hospital UTIs
Different ratios
Which media to isolate UTIs
Cysteine-lactose-electrolyte-deficient (CLED) media
-rich media containing lactose and lacking electrolytes (salt) to repress swarming
Subsequent plating on Macconkey agar if E.coli suspected (although Gram stain informative)
NB: some labs use a variant on CLED containing acid fuchsin (pH indicator) called CLED Andrade indicator media – stains E.coli pink
E.Coli colonies
Andrade - pink
Normal plate: large yellow colonies, opaque, centre slightly deeper yellow
Proteus colonies
Translucent blue colonies
Staph aureus colonies
Deep yellow colonies, uniform in colour
Staph coagulase-naegative (saprophyticus) colonies
Pale yellow colonies
E.Coli - UPEc
Gram-negative motile bacillus
Also causes GI-infections, but UTIs commonly caused by specific strains of E.coli known as UPEC
These differ at the genome level from enteric strains by having up to 1000 extra genes
Possesses potent adhesins for attachment to epithelium
UPEC Pilus adhesins (DIAGRAMS)
Type I pili: binds mannose receptors, common on glycoproteins in uroepithelium
P-fimbriae: binds to globobiose (aD-Gal-(1,4)-aD-Gal)
-linked ceramide host lipids
-often found in pyelonephritis strains
Further diagnosis of UPEC
Lactose fermenting strain so will produce pink colonies on MacConkey agar (and CLED andrade)
-E.coli pink
Strain designation by PCR and sequencing
GP-level urinary dipsticks
Level of nitrites
-indicative of gram -ve (usually E.coli)
Levels of luekocytes produced
Levels of pH, blood, protein, glucose, ketone etc.
Proteus mirabilis
Type of proteus spp.
Fabulous swarmer
-swarming: ability to move over a surface
-proteus can swarm over catheter surfaces
-can cover CLED plates / CLED plate suppresses this action?
More common in older patients
-can cause confusion
Proteus mirabilis - virulence factors
Urease: urea» ammonia + CO2, raises pH of urine»> can cause precipitation of minerals to form kidney and bladder stones
-smells really bad
IgA protease- reduces flushing…
Many pili adhesins
