Week 3- Introduction to infection Flashcards
Define infection
Invasion + multiplication of microbes in an area of the body they are not normally present which leads to disease
Can be asymptomatic + subclinical OR symptomatic + clinical
What are the risk factors for infection?
1) Extremes of age
2) Stress/ starvation
3) Compromised barriers to infection
>Physical
>Biochemical
4) Immunocompromised host:
>Primary immunodeficiency
>Secondary immunodeficiency
>Immunosupression
Define Symbiotoic
Close + oftern long term relationship between two different species (mutralistic/ commensal/ parasitic)
Define commensal
Symbiotic relationship between two different species where one derives some benfit from the other and the other is unaffected
Define colonisation
When a microbe grows on or in another organism without causing disease
Talk about Host-Microbe Interaction:
Examples of normal commensal bacteria
Where they exsist
What their role is
What is the affect of Abx
Normal commensal bacteria = “normal flora” “microbiota”
Exsist: GI tract, Upper + Lower airways, Skin, Mouth, Genital tract
At least commensal + probably mutralisitc
Prevent more pathogenic bacteria occupying the area
Abx eliminates normal flora, makes infection more likely
What are the two types of barrier immunity? List the examples
Physical:
1) Skin
2) Mucus
3) Resp Cilla
4) Commensal organisms
Biochem:
1) Sebaceous secretions
2) Lysozomes in tears
3) Spermine in sperm
4) Gastric acid
Most infections agents enter via ____ ____
of (4)
Most infectious agents enter via the mucosal surfaces of:
1) Nasopharynx
2) Respiratory tract
3) Alimentary tract
4) Genito-urinary tract
Bacteria Pathogensis (how bacteria cause disease)
What is needed?
Access : Reach a suitable site for adherence & invasion
Adherence : Stick or bind to a suitable site for invasion
Invasion : Penetrate the barriers to infection
Multiplication : Replicate to cause infection
Evasion : Evade the host immune system
Resistance : Resist anti-microbial treatments
Damage : Damage host cells (directly or indirectly)
Transmission : Released to infect other hosts
How do you prove the pathogen-disease link?
1) Finding microbes in an area of body they are not normally present
2) Correlate to clinical feature of patient
Urinary Tract is normally ____ but can become _____
Urinary tracts normally sterile, but can become colonised
What are the risk factors for UTI?
(Use the host risk factors discussed earlier)
? Necessary card
1) Extremes of age: Younger children + Older adults (post-menopausal
2) Stress & starvation : Not known to be a specific risk factor
3) Compromised barriers to infection :
Physical (anatomical) :
- Shorter female urethra (especially if sexually active or post-menopausal)
- Malformations (PKD, renal & ureteric malformations, strictures)
- Internal obstructions (stones or tumours)
- Bladder outflow obstruction (pregnancy, prostate enlargement)
- Iatrogenic (urinary catheters, operations, post-operative changes)
Immunocompromised host : UTI more common with diabetes mellitus
What is the bacterial pathogenesis of UTI?
Access : Most bacteria causing UTI are found in colon (eg.commensals)
Adherence : Pili (fimbriae) & adhesin molecules
Invasion : Haemolysin increases invasive potential
Multiplication : Colonisation of urinary tract may precede infection
Evasion : Relatively few immune cells in urinary tract
Resistance : Many bacteria causing UTI have multi-drug resistance
Damage : Causes Urethritis, cystitis, pyelonephritis, nephritis & septicaemia
Transmission : Easily passed out in urine (limited infection risk)
How do you diagnosis UTI (symptoms, risk factors, signs)
Symptoms:
- Dysuria, frequency or urgency of micturition*
- Haematuria, opaque or malodorous urine*
- Lower abdominal or loin pain*
Risk factors :
- Age*
- Compromised barriers to infection*
- Immunocompromised*
Signs :
- Lower abdominal or loin tenderness*
- Fever or septic shock*
What are the investigations you would carry out for a UTI?
Urinalysis:
WBCs, blood, nitrite, protein
MSSU:
M+C+S
Blood investigations:
FBC, U&E, CRP
Blood cultures:
for bacteria
Imaging:
USS, CT urogram
