Intro to Microbial Infection Flashcards
(32 cards)
Define commensal
A microorganism which forms part of the normal host microbiota
Define pathogen
A microorganism capable of causing infection
Define pathogenicity
The capacity to cause disease
Define virulence
The measure of the capacity to cause disease
Koch’s Postulates
- criteria x4
- Bacteria must be present in every case of the disease
- The bacteria must be isolated from the host
- The disease must be reproduced when a pure culture of the bacteria is inoculated into a host
- The bacteria must be recoverable from this host
Koch’s Postulates
- BUTs x2
- Some bacteria aren’t culturable
- Not always possible to get a susceptible host
Tissue tropism
- what
- BUT
- A pathogen’s affinity fro a specific tissue
- The region of colonisation isn’t necessarily where the infection will present
Factors that influence tissue tropism x4
- Presence of cell receptors
- Transcription factors
- Local temp & pH
- Physical barriers
Infections process
- the 2 main ways
- Invading host tissue
- Exerting their effects from mucosal surfaces
Steps of infections x6
- Recognition
- Attachment & entry
- Multiplication
- Evasion of host defences
- Shedding (escaping host)
- Damage
Why are many pathogens often needed to increase survival & cause disease? x2
- Many are often needed to enter
- Also as the hosts have defences
Factors that lead to infection of a healthy host x3
- Specific attachment mechanisms
- Pathogens are introduced INTO host
- Host defences are impaired
3 types of pathogens (based on ability to cause disease)
- Obligate
- Conditional
- Opportunistic
Obligate pathogen
- what
- example
- Almost always lead to disease
- e.g. HIV
Conditional pathogen
- what
- example
- May cause disease if conditions are met
- e.g. Staphylococcus aureus
Opportunistic pathogen
- what
- Usually only infects immunocompromised host
Define virulence factors
Factors that drive infection
Examples of virulence factors x7
- Toxin secretion
- Antibiotic resistance
- Pilus formation (can bind w host)
- Capsule (protects)
- Iron transport systems
- Adhesion factors (promote tropism & adherence)
- Enzymes
2 types of bacterial toxins
- Endotoxins
- Exotoxins
Endotoxins
- toxicity
- affects which bacteria
- how work
- example
- Low
- Gram -ve (in cell walls)
- Often associated w an immune response
- Often lipids
Exotoxins
- toxicity
- affects which bacteria
- how work
- example
- High
- Gram +ve & -ve
- Secreted, can manipulate host’s immune system
- e.g. tetanus toxin
3 factors that affect transmission
- Number shed
- Number required to inject a fresh host
- Their stability in the environment
Routes of transmission x5
- Vertical
- Horizontal
- Zoonoses
- Fomite
- Nosocomial
Example of disease transmitted through vertical transmission
HIV
