Pathogenicity of microorganisms Flashcards
Define principles of infection
Primary - root of problem
Secondary - Complicated because of the root
Mixed
Define principles of course of infection
Incubation period - Growth rate
Illness - signs and symptoms
Convalescence - recovery from disease
Carriers - Individuals who may harbour and spread infectious agent
Define principles of pathogen
Primary - When person is healthy
Opportunistic - When person is weak
Define distribution of pathogen
Localised - infectious agents in which is limited to small area
Systemic infection - dissimulated out of the body
Bacteraemia - condition that relates to the presence of viable bacteria in the bloodstream
Septicaemia - acute life threatening illness
Toxaemia - Toxins of the infectious agents circulating in the bloodstream
Viraemia - viruses in the bloodd
What is Kochs postulates (original)
- Microbe is only found in diseased, not healthy individuals
- The microbe should be able to be isolated from the host and grown in pure culture
- The same disease should be produced when the pure culture is introduced to a healthy and susceptible host
- The same organism must be recoverable from the experimentally infected host
What were Kochs limitations?
- Pathogens found in both healthy and diseased individuals
- Not all organisms can be cultured
- Not all infectious caused by a single organism
- Not suitable animal models for disease (if disease is human only)
-However still valid and being used to prove associations between microbes and disease
What is Kochs postulates (modified)
- The gene and/or its products should be found only in pathogenic strains of organism and not in avirulent strains
- Inactivation of the suspected gene(s) associated with pathogenicity should result in a measurable loss of pathogenicity
- Reversion of the inactive gene should restore the disease phenotype (complementation or rescue)
Explain the bacterial genome
Chromosome - single circular double stranded DNA that carries all genes
Plasmid - small circular ds-DNA carries nonessential genes (toxins
Bacteriophages (phages) - virus replicating inside bacterial cell - genes are horizontally transferred between bacteria by transduction
Pathogenicity islands - mobile gene clusters that encode virulence factors
What is lytic phage
Results in lytic cycle which is cell death by lysis and new phages released
What is temperate phage
Results in lysogenic cycle where phage DNA integrates into bacteria chromosome (called prophage) - host cell survives and phage DNA replicates part of hosts chromosome
What are the stages of pathogenesis?
- Adherence to host cells
- Nonspecific
Hydrophobic interactions
Biofilm - Specific (adhesions)
- Nonspecific
- Colonisation and invasion
- Nutrient acquisition
Iron
Extracellular degradative enzymes - Invasion
Motility, express membrane proteins, extracellular enzymes
- Nutrient acquisition
- Evade the immune response
- Capsule, biofilm, structural adaptations, bacterial proteins, intracellular bacteria
- Produce damage - substances harm the host
- Extracellular enzymes
- Toxins
What is the impact of adherence on bacteria
Allows bacteria to colonise
Required for release of virulence factors
Forms biofilms
What is the impact of adherence on host cells?
Manipulate host cell signalling
Elicit immune responses
What are the extracellular degradative enzymes for nutrient acquisition?
Proteases
Lipases
Glycohydrolase
Lecithinase
What are the bacterial mechanisms of iron acquisition?
Siderophores
- Iron chelators secreted by bacteria that bind to Fe3+
- Capture iron from the host by chelation and then binds to specific receptors on the bacterial surface
Bind to host iron-binding proteins
- Ferritin, transferrin, lactoferrin on haemin
Iron substitution
- Some organisms do not need iron to grow
