Bacterial Pathogenesis Flashcards
Define pathogen
a microbe that harms the host/causes disease
Define commensal
: a microbe that does not cause harm and that is typically considered part of the normal flora
Define Saprophyte
feeds on and decomposes dead organic material
Define Infection
the colonisation of host by micro-organisms that have the potential to cause disease (& associated disease?)
Define Infectious disease
damage to host by micro-organisms that impair host function
Define Pathogenesis
PATHOGENESIS of a disease = the biological mechanism(s) that lead to the diseased state.
Define Virulence
Define virulence factors
- the relative ability of a pathogen to cause disease in the host
- are mechanisms/products of pathogens that promote their ability to cause infection and disease. considered to be 2 major types: 1) Factors promoting colonisation/invasion of host
2) Factors causing damage to host
Define opportunistic pathogen
can be part of the normal flora BUT may be harmful if they move from one part of the body to another
Define strict pathogen
always associated with disease
Colonisation and infection?
COLONISATION is not the same as INFECTION
BActeria and pathogenesis
- Few bacteria are ALWAYS pathogenic and this is dependent on the host species
- Some bacteria are potentially pathogenic e.g. E coli
- Most bacteria are never pathogenic
what 2 major components are considered as part of abcteria pathogenesis
- The bacterial virulence factors that damage or alter the host cells & tissues e.g. toxins, secretion systems, adhesins
- The host response: especially including the immune and/or inflammatory response that may lead to damage
What are the steps to bacteria pathogensis?
EAICoVID
Eat apples in covid
1. Exposure to pathogen
2. Adhere to skin or mucosa
3. Invasion through epithelium
4. Colonisation and growth. Production of virulence factors
THEN both/ either or:
5. Additional virulence factor interaction with host e.g. toxins
5. Invasiveness = further growth at original and distant sites
6. Tissue damage, disease
What are examples of pathogen determinants
Virulence Environmental stability Route of entry Infective dose Tissue tropism Susceptibility to host defense
Examples of host determinants
Species Breed Age Sex Genetic factors Physiological factors Immune competence
Examples of bacterial virulence factors
- exotoxins
- Proteases
- Capsule
- Pilli
- Adhesins
- Flagellum
- Plasmid
- Bacteriophage
What did Koch’s prostulates help discover?
- Bacillus anthracis was the first bacterium proven to be the causative (AETIOLOGICAL) agent for a disease, anthrax (Anthrax is a serious infectious disease caused by gram-positive, rod-shaped bacteria known as Bacillus anthracis.)
- Agents of cholera and tuberculosis
list 4 of Koch’s prostulates
1) The microbe should be found in all cases and at all sites of the disease.
2) The microbe should be isolated from the infected persons and maintained in pure culture.
3) The pure cultured microbe should cause symptoms of the disease on inoculation into a susceptible individual.
4) The microbe should be reisolated from the intentionally infected host.
Limitations of Koch’s Prostulates
1) Viruses/some bacteria/parasites cannot grow independent of host
2) Asymptomatic carriers
3) Opportunistic pathogens
4) Polymicrobial diseases
Describe Falkow’s adaptation of Koch’s postulates for identification of virulence factors
1) Phenotype under investigation should be associated with pathogenic members of a Genus or pathogenic strains of a species.
2) Specific inactivation of genes associated with a suspected virulence trait should lead to a measurable loss in pathogenicity or virulence.
3) Reactivation of the mutated gene should lead to restoration of pathogenicity
Colonisation and growth
Pathogen must find relevant environment for growth
Some organisms often remain localised, producing small focus of infection (eg. Boils)
Generalised infections occur due to bacteraemia – pathogen in bloodstream
Some pathogens multiply in blood plasma producing toxic waste products e.g. endotoxin causing – septicaemia
What are examples of secreted virulence factors. What do they aid? What do they often break down?
- AID: secreted extracellular proteins can aid establishment & maintenance of pathogens
- often break down host tissues:
EXAMPLES:
Coagulase- clots plasma, protecting against host defences
Proteases- degrade protein
Nucleases- degrade nucleic acids
Leukocidins- kill leukocytes
Haemolysins- lyse erythrocytes, causing anaemia & releasing iron for microbial growth
What is an exotoxin?
protein released by an organism as it grows that has toxic effects
How are exotoxins defined?
- enterotoxins - intestinal mucosa
- neurotoxins - nerve tissue
- cytotoxins - general tissue
How do bacteria become pathogenic?
Horizontal gene transfer:
- Uptake of naked DNA from the environment
- Direct transfer of plasmid DNA between bacteria
- DNA transfer mediated by bacteriophages
What are plasmids
Circular double-stranded DNA molecules that replicate independently of the chromosome.
2. can carry virulence genes e.g. toxins
