4 – Host-Microbe Relationship Flashcards
Koch’s Postulates
- Organism in diseased animals but not healthy ones
- Isolate in pure culture
- Introduce to a healthy animal and make it sick
- Re-isolate it
Pathogen
- Organism CAPABLE of causing disease
Virulence
- Relative ability of an organism to cause disease
Virulence factor
- Property of an organism which allows it to establish within a host and/or cause disease
Pathogenesis
- Processes and host-organism interactions which leads to disease
Host microbe interactions from the host’s perspective
- SPECTRUM
o From benefit (colonization) to indifference (latency) to damage (disease)
Infections occur when
- Overwhelming pathogen load
- Comprised host defenses
Disease/pathology/damage results from
- Production of toxins
- Invasion of tissues
Fundamentals of pathogenesis
- Associate
- Multiply
- Evade
- Damage co-opt
- Transmit
Virulence factors
-structures used for attachment
-flagella
-siderophores
-capsule
-secretion systems
-toxins
-superantigens
-enzymes
- Structures used for attachment
o Staphs and Streps – MSCRAMMs (microbial surface components recognizing adhesive matrix molecules)
Bind to host ligands and can prevent opsonization (anti-phagocytic)
o Fimbrae
Bind to intestinal epithelium in pigs and calves
- Flagella
o Reach the site of infection (ex. E.coli)
Motility test
- Siderophores
o Chelators allow bacteria to capture iron in very low concentration environment
- Capsule
o Polysaccharide structure
o Interferes with innate immune system
o Can protect from bacteriophages
- Secretion systems
o Structures that transport molecules across the cell envelope (‘needle-like’ apparatus)
- Toxins
o Endotoxins – LPS (found in most gram negative bacteria)
o Exotoxins – botulinum toxin, cholera toxin
- Superantigens
o Non-specifically bind to and activate the T-cell receptor = CYTOKINE STORM
Systemic inflammation, DIC, shock, death
Degrees of pathogenicity (‘damage-response’ framework)
-accidental pathogen (saprophytes)
-opportunistic pathogens
-obligate pathogen
- Accidental pathogen (saprophytes)
o Rhodococcus equi
Cause of pneumonia in foals, likely due to decline in maternal immunity
o Aspergillus
Ubiquitous in nature
Decomposing matter
Cause of pneumonia in birds and allergic airway disease in horses
- Opportunistic pathogens
o Most clinically relevant organisms
o Gain access to a normally sterile site=infection
Staphylococcus spp. (mastitis, UTI)
E.coli
Primary vs. secondary infection
- Important to find out WHY your patient has an infection
o Primary disease in patient?
o Poor management?
Epidemiological triad (ex. Haiti)
- Host
- Agent
- Environment
Zoonoses
- Infectious disease caused by a pathogen and jumped from non-human to human
- Ex. SARS-CoV2, Ebola, Salmonella