Week 7 CTL Notes
Microbial Diversity
- Some bugs are good (even essential) and some bugs are bad.
- Organisms capable of causing disease are pathogens
Normal Flora (commensals)
• Heavily colonise skin – armpit, perineum, interdigital areas
• Nose and oropharynx
• GI Tract
• Uro-genital tract.
• Are normal at certain places where they are not harmful.
o However when they colonise an area where they shouldn’t, they cause disease
(nosocomial infection).
§ Known as opportunism.
Pathogenesis
• The biochemical mechanisms whereby microbes (bacteria, fungi, parasites & viruses) causes
disease.
• Virulence: the propensity of a microbe to cause infection à disease.
Steps to disease:
I. Entry
• Oral
• Skin
• Trans-placental
• Inhalation
• Inoculation (wound/skin penetration)
• Sexual
II. Colonisation
• Breach of skin/epithelia/conjunctiva
• Attachment
III. Persistence + avoiding host defences.
• Beat natural barriers – flushing, mucous + cilia, stomach pH, Lysosomes in saliva, etc.
IV. Replication
• Mucosal (GI tract)/systemic (blood)/nerves (viruses)/cerebrospinal fluid (meningitis)
V. Dissemination – (Host-Host)
• Faecal-oral (diarrhoea), Aerosols (sneezing), Sexual (intercourse)
• Depends on:
o Organism size
o Ability to survive in external environment
VI. Cause Disease
• Can release toxins – either local effects / or systemic
• Can cause unusual cellular activity
• Can cause tissue damage
www.MedStudentNotes.com
Microbial Diversity
- Some bugs are good (even essential) and some bugs are bad.
- Organisms capable of causing disease are pathogens
Normal Flora (commensals)
• Heavily colonise skin – armpit, perineum, interdigital areas
• Nose and oropharynx
• GI Tract
• Uro-genital tract.
• Are normal at certain places where they are not harmful.
o However when they colonise an area where they shouldn’t, they cause disease
(nosocomial infection).
§ Known as opportunism.
Pathogenesis
• The biochemical mechanisms whereby microbes (bacteria, fungi, parasites & viruses) causes
disease.
• Virulence: the propensity of a microbe to cause infection à disease.
Steps to disease:
I. Entry
• Oral
• Skin
• Trans-placental
• Inhalation
• Inoculation (wound/skin penetration)
• Sexual
II. Colonisation
• Breach of skin/epithelia/conjunctiva
• Attachment
III. Persistence + avoiding host defences.
• Beat natural barriers – flushing, mucous + cilia, stomach pH, Lysosomes in saliva, etc.
IV. Replication
• Mucosal (GI tract)/systemic (blood)/nerves (viruses)/cerebrospinal fluid (meningitis)
V. Dissemination – (Host-Host)
• Faecal-oral (diarrhoea), Aerosols (sneezing), Sexual (intercourse)
• Depends on:
o Organism size
o Ability to survive in external environment
VI. Cause Disease
• Can release toxins – either local effects / or systemic
• Can cause unusual cellular activity
• Can cause tissue damage
www.MedStudentNotes.com
