Week 3-UTI Flashcards
Revise host microbe interactions and infection
Interactions can be:
Symbiotic –> close, often long term interaction between two different species (mutualistic/ commensal/ parasitic)
Commensal –> Symbiotic relationship between two different species where one derives some benefit and the other is unaffected
Colonisation –> when a microbe grows on or in another organism without causing any disease
Infection = invasion and multiplication of microbes in an area of the body where they are not normally present, usually leads to disease
List host risk factors for infection
- extremes of age
- stress
- starvation
- compromised barriers to infection:
- physical (anatomical)
- biochemical (physiological)
- Immunocompromised host
- primary immunodeficiency (from birth)
- Secondary immunodeficiency (acquired after birth)
- Immunosuppression (iatrogenic from immune suppressing treatment).
What are normal commensal bacteria?
Normal commensal bacteria = “normal flora” or “microbiota”
Occupy the majority of available body areas such as skin, mouth, upper airway/lower airway, GI tract, genital tract
They are at least commensal and probably mutualistic in preventing more pathogenic bacteria from occupying those areas.
Antibiotic tx eliminate normal flora and make infection more likely.
This is less relevant in “sterile site” infections (e.g. UTI)
Describe the stages of bacterial pathogenesis
A A Its MERDT
Access –> reach suitable site
Adherence –> bind to site
Invasion –> penetrate barriers
Multiplication –> replicate
Evasion –> avoid host immune sx
Resistance –> resist antimicrobial tx
Damage –> damage host cells
Transmission –> released to infect other hosts
What does the urinary tract include in men/ women?
How does urinary tract infections enter the body?
Where do most organisms that cause UTI come from?
Why is UTI more common in women vs men?
Urethra, bladder, ureters, kidneys (both)
prostate in men
UTI’s enter the body via the urethra –> male and female urinary tracts are normally sterile but can become colonised
Bacteria that cause UTI are most commonly from the anus
UTI’s are more common in women than men due to the shorter distance between the urethral opening and the anus, and the shorter length of the urethra.
What are the types/ sites of UTI?
Inflammation of the urethra = urethritis, often included in STI heading (gonorrohea etc)
Inflammation of prostate = prostatitis
Inflammation of the bladder = cystitis, most common (also called lower UTI)
Once infection reaches the kidneys (travels via the ureters) it is called pyelonephritis. Infection tends not to occur in the cortex (where it would be called nephritis) but in the pelvis region, essentially forms an abcess.
Pyelonephritis can be very severe, pts can become septic and may require surgical drainage.
What are the host risk factors for UTI?
- Extremes of age –> younger children and older adults (post menopausal women)
- Stress and starvation (not known to be specific to UTI)
- Compromised barrier to infection:
- Shorter urethra in women (esp. if sexually active / post menopausal)
- Malformations (pKD, renal and ureteric malformations, strictures)
- Internal obstructions (stones/ tumours)
- Bladder outflow obstructions (pregancy, prostate enlargement)
- Iatrogenic (urinary catheters, operations, post operative changes)
- Immunocompromised host –> UTI more common with diabetes mellitus (increased sugar content of urine and mild immunosuppresive effect of DM)
Describe the bacterial pathogenesis in UTI
Access —> most bacteria causing UTI found in the colon (e.g. commensals)
Adherence –> Pili (fimbriae) and adhesin molecules
Invasion –> Haemolysin (breaks down RBC, same enzyme can break down tissue) increases invasive potential
Multiplication –> colonisation of urinary tract may precede infection
Evasion –> relatively few immune cells in urinary tract
Resistance –> many bacteria causing UTI’s have multi drug resistance
Damage —> causes urethritis, cystitis, pyelonephritis, nephritis and septicaemia
Transmission –> easily passed ou in urine (limited infection risk)
What are some of the common causitive agents of UTI?
Escherichia coli --> gram negative bacilli from the colon
other “coliforms” (e.g. klebsiella, enterobacter) = gram -ve from colon
Staphylococcus saprophyticus = Gram +ve cocci from perineum and vagina
Enterococci spp. (faecal streptococci) = Gram =ve cocci from colon
Pseudomona spp. Gram -ve bacilii from the environment
Tuberculosis = variable gram staining bacilli from systemic infection
STI’s –> (neisseria gonorrhoeae, chlamydia spp.) –> urethritis
Describe the process of diagnosis of UTI?
1) symptoms –> dysuria, frequency, or urgency of micturition
haematuria, opaque or malodorous urine
Lower abdominal or loin pain
2) Risk factors –> age (young child/ elderly) compromised barrier to infection or immunocompromised (e.g. diabetes)?
3) Signs –> Lower abdominal or loin tenderness (sign its spread to kidneys), fever or septic shock
4) investigations –> urinalysis w dipstick for WBC’s, blood, nitrite (produced by bacteria), protein (inflammatory marker)
Mid stream specimen of urine for M + c + s (microscopy, culture and sensitivity)
blood investigations (FBC, Uand E, CRP)
Blood cultures (for bacteria, only in patients with fever)
Imaging (USS, CT, urogram (contrast within the urinary tract then CT done) (done if the infection is resistant, persistent, recurring).
What is required for microbiological urine sample?
Midstream urine sample to obtain uncontaminated urine sample
Clean with antiseptic wipe, then patient collects midstream to get good sample.
What are the microscopic markers of UTI?
What suggests infection? What suggests renal disease? What suggests contamination?
How could you use microscopy to target treatment?
1) microscopy –> WBCs > 100/ ul suggests infection
RBC suggest haemorrhage or infection
Casts (collections of cells stuck together, composition of WBC/ RBC, sign of inflammation) suggests renal disease
epithelial cells suggests contamination of sample
2) Culture –> CFUs (colony forming units) > 100/ ul suggests infection
3) Sensitivities –> tested with app. range of antibiotics
What cells can be seen on MS?
Large multinucleate cell = WBC
Smaller biconcave cell = RBC
Larger cell = epithelial cell suggesting some contamination
Tiny black marks = bacteria
Outline the approaches to antibiotic therapy in UTI tx?
MSSU sample and microscopy, culture and sensitivity to identify the organism and app. antibiotic.
This is targeted therapy -> specific therapy based on confirmed diagnosis
Empirical therapy approach –> best guess, therapy w/out confirmed diagnosis ( in emergency cases, cannot wait 24 hrs for culture)
Prophylactic –> preventative therapy to prevent UTI from occuring (rare as this breeds resistance).
Outline treatment approaches for UTI
1) only treat in cases when they meet the criteria for diagnosis –> WBC’s > 100/ ul + CFU > 100/ ul
Low epithelial cell count (avoided contaminants)
Good correlation with clinical features and other investigations
2) If there is colonisation but no features of infection (e.g. no white cells/ raised protein in urine/ no symptoms) then only treat in children and pregnant women (risks tx outweigh benefits otherwise)
3) If pt has urinary catheter only treat if there is evidence of infection (as urinary catheters always lead to colonisation). Catheter should be changes during treatment.
Any change of urinary catheter can make colonisation, leading to infection, give prophylactic antibiotics when doing this.
