An overview of different pathogens, how they are transmitted, and how they affect the human body. Also includes the body's response to the different pathogens. Aims to help pre-clinical students understand the basis for infection and diseases.
When considering microbes, we think of the susceptibility, virulence (if good at causing disease- it has
virulence factors) and the treatment, prevention and source of it.
Urinary Tract Infections (UTIs):
Incidence of UTI varies with age and sex- females are at far higher risk of UTI than males (except at
extremes of age).
UTI in babies/ pre-school children- need quick identification and treatment because recurrent
infection in this group can cause damage to the kidneys that are developing. If the UTI is recurrent-
maybe something structurally wrong with urinary tract.
Female are more susceptible as they have a shorter urethra and the tract opening is close to the anus
so greater chance of transfer.
In females the incidence of UTI increases with sexual activity.
Important to check for UTI while pregnant and just general regular testing as they may be
asymptomatic UTIs. They can impact the early delivery of a child.
Increasing incidence with older age due to:
Post-menopausal women- hormone and microflora changes
Prostate issues in men – growth/obstruction
Catheterisation (reasons include obstruction, neurological issues) can occur at any age and increases
chance of getting a UTI.
UTIs are the most common healthcare
associated infections + most common in
community
The urinary tract is designed to allow the
flow of urine in one direction e.g. having
the cysto-ureteric valve prevent any kind
of reflux back to the kidney.
If child has recurrent UTIs he may have a
problem in one of the following areas
shown- bladder, kidney and junction etc.
When you get a UTI, organisms can come
in through two directions:
The can either come from
bacteraemia or sepsis infections via the renal vein and sometimes the renal artery –
descending infection.
Much more commonly is the ascending route where it goes up the tracts having come from
outside and goes up the urethra to the bladder and up the ureter to the kidneys.
The infection doesn’t necessarily occur in the tracts such as the ureter but can be of the bladder
(cystitis) or the kidney (pyelonephritis), giving the symptoms:
Cystitis (inflammation of bladder):
- Increased urinary urgency & frequency
- Dysuria – painful urination
- Lower abdominal pain
- WBCs and bacteria in urine
- Raised temperature
Pyelonephritis (inflammation of kidney):
- Same as above
- Flank pain
- High fever
- Malaise
- Confusion / restlessness
- Nausea
, Usually in elderly people the UTI is picked up as they are acting erratically- showing signs of confusion
+ disorientation.
Diagnosis of UTI is done via urinalysis (give hint of whether blood present, nitrates etc in urine) –
giving indication whether there is infection. You could also carry out a urine culture- allows to
differentiate the microbes causing infection by colour. Look for presence then treat accordingly. You
could also diagnose via sensitivity testing- testing if microorganism is sensitive or not.
Most common microbes that cause UTIs are:
Some of these are organisms which you may find in your gut (microflora) and have been misplaced
due to the proximity e.g. E. coli (most common), Klebsiella, Proteus Mirabilis and less commonly
Pseudomonas. From gram positive – Saprophyticus and less commonly enterococcus faecalis.
Healthcare associated have similar pattern, but pseudomonas is more common. Gram negative are
more common.
Looking at uncomplicated UTI (straightforward UTI affecting lower tract i.e. not the kidney), they are
most commonly caused by uropathogenic E. coli.
Complicated UTIs (more at risk in healthcare setting e.g. catheter etc) are caused by a more diverse
range of organisms.
You would treat these UTIs by seeing what the most likely organism is. Look at local guidance as to
which antibiotic is suitable (i.e. bacteria will not show resistance to) and check the resistance patterns.
If the case is complicated or recurrent then you need to culture the bacteria and asses sensitivity.
Characteristics which help the microbe to cause infection (virulence factors- help organism to colonise
and spread) include:
Adhesion - e.g. pili
Invasion – e.g. haemolysin
Motility – e.g. flagella
Biofilm formation – seal of itself and avascular so no antibiotic can reach it – protective
barrier.
Uropathogenic E. coli: gram negative bacteria
Usually transferred from gut flora (endogenous infection)
Express pili – attachment and microbe can ascend urinary tract, normally urine is flowing,
and it will wash away organisms that are on the tract + the surface of the tract is shed on
regular basis to get rid of microbes, but E. coli can escape this and quickly ascend the tract.
Invade and destroy within bladder (uncomplicated) to obtain/release nutrients.
This UPEC can invade and penetrate cells, multiply inside and cause destruction (cause cells to move
off surface) to obtain nutrients and ascend to cause kidney infection and sepsis (near blood vessels
so vulnerable).
Sexually Transmitted infections:
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