4 – Host-Microbe Relationship

Question 1

Koch’s Postulates

Answer 1

• Organism in diseased animals but not healthy ones
• Isolate in pure culture
• Introduce to a healthy animal and make it sick
• Re-isolate it

Question 2

Pathogen

Answer 2

• Organism CAPABLE of causing disease

Question 3

Virulence

Answer 3

• Relative ability of an organism to cause disease

Question 4

Virulence factor

Answer 4

• Property of an organism which allows it to establish within a host and/or cause disease

Question 5

Pathogenesis

Answer 5

• Processes and host-organism interactions which leads to disease

Question 6

Host microbe interactions from the host’s perspective

Answer 6

• SPECTRUM
  o From benefit (colonization) to indifference (latency) to damage (disease)

Question 7

Infections occur when

Answer 7

1. Overwhelming pathogen load
2. Comprised host defenses

Question 8

Disease/pathology/damage results from

Answer 8

1. Production of toxins
2. Invasion of tissues

Question 9

Fundamentals of pathogenesis

Answer 9

• Associate
• Multiply
• Evade
• Damage co-opt
• Transmit

Question 10

Virulence factors

Answer 10

-structures used for attachment
-flagella
-siderophores
-capsule
-secretion systems
-toxins
-superantigens
-enzymes

Question 11

• Structures used for attachment

Answer 11

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

Question 12

• Flagella

Answer 12

o Reach the site of infection (ex. E.coli)
 Motility test

Question 13

• Siderophores

Answer 13

o Chelators allow bacteria to capture iron in very low concentration environment

Question 14

• Capsule

Answer 14

o Polysaccharide structure
o Interferes with innate immune system
o Can protect from bacteriophages

Question 15

• Secretion systems

Answer 15

o Structures that transport molecules across the cell envelope (‘needle-like’ apparatus)

Question 16

• Toxins

Answer 16

o Endotoxins – LPS (found in most gram negative bacteria)
o Exotoxins – botulinum toxin, cholera toxin

Question 17

• Superantigens

Answer 17

o Non-specifically bind to and activate the T-cell receptor = CYTOKINE STORM
 Systemic inflammation, DIC, shock, death

Question 18

Degrees of pathogenicity (‘damage-response’ framework)

Answer 18

-accidental pathogen (saprophytes)
-opportunistic pathogens
-obligate pathogen

Question 19

• Accidental pathogen (saprophytes)

Answer 19

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

Question 20

• Opportunistic pathogens

Answer 20

o Most clinically relevant organisms
o Gain access to a normally sterile site=infection
 Staphylococcus spp. (mastitis, UTI)
 E.coli

Question 21

Primary vs. secondary infection

Answer 21

• Important to find out WHY your patient has an infection
  o Primary disease in patient?
  o Poor management?

Question 22

Epidemiological triad (ex. Haiti)

Answer 22

• Host
• Agent
• Environment

Question 23

Zoonoses

Answer 23

• Infectious disease caused by a pathogen and jumped from non-human to human
• Ex. SARS-CoV2, Ebola, Salmonella