Intro to infection

Question 1

What are the 3 types of host-microbial infections?

Answer 1

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 - the invasion and multiplication of microbes in an area of the body where they are not normally present, which usually leads to disease

Question 2

What is a symbiotic relationship?

Answer 2

close and often long-term interaction between two different species (mutualistic / commensal / parasitic)

Question 3

What are normal flora/microbiota what do they do?

Answer 3

Normal commensal bacteria - occupy skin, mouth, upper airways, lower airways, gastro-intestinal tract & genital tract. They are at least commensal & probably mutualistic in preventing more pathogenic bacteria from occupying those areas.
Ab use can eliminate these flora

Question 4

What are the host risk factors for infection?

Answer 4

Extremes of age
Stress and starvation
compromised barriers to infection
Immunocomprimised host

Question 5

What are the 2 types of barriers to infection? (give examples of each)

Answer 5

Physical barrier (skin, mucus, respiratory cilia, comensal organisms)
Biochemical barrier ( Sebaceous secretions in skin, Lysozyme in tears, Spermine in sperm, Gastric acidity)

Question 6

List investigations which can be carried out for diagnosing infecions.

Answer 6

Markers of inflammation - blood/bodily fluids
Microscopy, culture & sensitivity (m, c & s) testing for bacteria
Nucleic acid (DNA / RNA) detection (usually PCR) for viruses
Antibody detection (serology) for viruses & unusual pathogens
Antigen detection (of a microbial component) for unusual pathogens
Imaging studies (X-rays / US / CT / MR) to look for a focus

Question 7

Why are females more likely to get UTIs?

Answer 7

Urethra is shorter

Urethra closer to anus

Question 8

What are the host risk factors for UTIs?

Answer 8

Younger children and older adults (post-menopause)
Shorter urethra (sexually active/post-menopause)
Malformations
Internal obstructions (stones. tumours)
Bladder outflow obstructions (pregnancy, prostate enlargement)
Iatrogenic (catheters, ops, post-ops)
Immunocomprimised host (diabetes)

Question 9

How do bacteria cause pathogenesis in UTIs? (hint: access, adherence, invasion, multiplication, evasion, resistance, damage, transmission)

Answer 9

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)

Question 10

How can you diagnose UTIs? (symptoms, risk factors, signs and investigations)

Answer 10

S: Dysuria, frequency or urgency of micturition, Haematuria, opaque or malodorous urine, Lower abdominal or loin pain
RF: age, diabetes
S: Lower abdominal or loin tenderness, Fever or septic shock
I: Describe earlier