Lec 22 Flashcards
Draw a diagram of the overall disease process
Describe the term commensals
- decribes 1000s of bacterial species
- beneficial to the host but changes in the levels of gut microbiome can lead to the growth of pathogenic species
Describe the term zoonotic
- zoonotic disease has an animal resevoir
- commensal to that animal but can be transmitted and cause infections in humans
- eg Campylobacter jejuni - exist in chickens but can cause severe gastroenteritis in humans
- common for food-borne pathogens
Describe the 4 Koch’s Postulates
- IDENTIFICATION; pathogen must be present in te diseased state and follow its distribution, can be measured back to the site of lesion, absent from healthy individuals
- ISOLATION; grown in pure culture
- INNOCULATION; innoculation of this pure culture in a susceptible indivudal shoild cause the disease
- REIOSLATION; same pathogen should be reisolated from the 2nd animal
Give 4 examples of when Koch’s potsulates cannot be applied correctly
- sometimes pathogens can’t be grown in pure culture eg Chlamydia
- cultivation techniques lead to attenuation of the strain & loss of VFs
- animal models may not be available/may have different pathologys
- boutlism - caused by Clostridium botulinum TOXIN not the organism itself
Give and describe the 3 types of pathogen that exists
- STRICT; can only survive in the host (not environment), small genomes because highly adapted to specific niche within the organism (no commensals are present), requires person to person contact to spread
- OPPORTUNISTIC; present in the environment and can only infect in compromised individuals (eg immunocompromised, cuts, wounds), cannot spread from person; person, can include commensals in which changes to the host defence can cause growth of pathogenic organisms (previosuly commensals eg C. dificile)
- FACULTATIVE; survive in both host and environment, large genomes, includes the majority of pathogens, adaptations for both situations
Describe strain variation and give an example
not all strains of an organism are equally pathogenic eg E. coli strain 0157 encodes toxins that can kill but the majority of other strains are harmless
Give definitions for;
- pathogenesis
- pathogenecity
- virulence
- mechanism of disease
- ability of an organism to cause disease
- degree of pathogenecity
Describe ID50/LD50
dosage required for 50% infection/killing of population
infectious / lethal dose
Give 3 limitations of using ID/LD50
- animal may not be representative of what happens in human model eg may have higher or lower LD/ID50 values
- will show cumulative effect and not individual steps in the process
- may be misleading eg ID50 of vibrio cholerae is higher than that of shigella dysentry (suggesting that V. cholerae is less infectious) but we know that v. chloreae is fatal often however dysentry is seldom fatal
What is a virulence factor?
any product or strategy that contributes to the virulence/pathogenencity of an organism. often multiple VFs play a role
Give the 2 classifications of VFs
- COLONISATION/INVASIVENESS; allow the pathogen to colonise eg adhesins, defensins, evade immune system, nutrient acquisistion
- TOXIGENENCITY; causes damage to the host cell
Give the alternative classification of VFs
- dedicated (primary) - adesins, invasins, required to gain entry and exploit the host. only expressed inside the host
- non dedicatd (2ndry) - allow the pathogen to survive outside of the host. eg nutrient acquisation, motility, resistance to unfavourable pH, heat
Describe koch’s postulates for identifying VFs/molecular structures
- phenotype identification of pathogen
- a) mutation of the VF gene -> should lead to loss of virulence OR b) placing the VF gene into another non-pathogenic organism -> should get pathogenecity
- for a) complementation of the VF gene should restore pathogenencity
- expression of VF gene in diseased state/ host
- VF can sometimes provide protective immunity
