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
In an MSSU (Mid stream, specimen, urine) on MS+C what are you looking for with each?
Microscopy:
- WBC → >100 / μl = infection
- RBC → Haemorrhage or infection
- Epithelial cells → Contaminated
- Casts → Marker of kidney disease
Culture:
- CFUs (colony forming unit) >100 / μl → Infection
Sensitivites:
- Tested with appropriate abx
Define Pathogen
Microorganism able to cause disease
Obligate pathogen
Pathogen must cause disease to be transmitted from one host to another. Must infect to survive
Opportunisitic pathogen
Pathogen takes advanatge of an opportunity not normally available
Define Parasite
Old fashioned term for pathogens that are protazoa or metazoan
