Pathogens

Question 1

Microbes functions

Answer 1

-Nitrogen fixing bacteria help with plant growth
-Important for decreasing atmospheric CO2
-Help break down waste

Question 2

Disease causality- what makes a microbe pathogenic?

Answer 2

**Koch’s postulates

1. Microbe must be found in all organisms suffering from the disease, but should not be found in healthy organisms
2. Microbes must be isolated from a diseased organism and grown in pure culture
3. Cultured microbes should cause disease when introduced into healthy organisms

4.The microbe must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original causative agent

Question 3

Koch’s postulates and pathogens

Answer 3

According to Koch, very few organisms are pathogens.
>pathogenicity is host specific. A microbe for one species can be pathogens but to another species can be commensal

Question 4

Strict pathogens

Answer 4

-Rabies
-Yersinia pestis (plague)

Question 5

Pathogen

Answer 5

An organism capable of causing disease

Question 6

Virulence

Answer 6

The relative ability of an organism to cause disease

Question 7

Virulence factor

Answer 7

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

Question 8

Pathogenesis

Answer 8

The processes and host-organism interactions which leads to disease

Question 9

Host microbe interactions

Answer 9

**spectrum

1.Benefit (colonization)
2.Indifference (latency)
3. Damage (disease)

Question 10

When do infections occur?

Answer 10

1.Overwhelming pathogen load
2. Compromised host defences

Question 11

What does disease result from?

Answer 11

1.Production of toxins
2. Invasion of tissues

Question 12

Fundamentals of pathogenesis

Answer 12

1.Associate
2. Multiply
3. Evade
4. Damage co-opt
5. Transmit

Question 13

Pathogenesis associate stage

Answer 13

Enter body or reach site of infection (anatomical location, cell type or receptor)

Question 14

Pathogenesis multiply stage AND evade stage

Answer 14

Acquire and utilize nutrients, multiple and reach a critical number while avoiding host defence
>some pathogens have a capsule which will help them evade complement and phagocytosis

Question 15

Pathogenesis damage co-opt stage

Answer 15

Damage from pathogen or host response
>may include hijacking host processes

Question 16

Pathogenesis transmit stage

Answer 16

Pathogen must get out, survive, infect and repeat

Question 17

Virulence factors

Answer 17

1. Essential virulence genes- cause damage to host
2. Virulence associated genes- required for expression, secretion, or processing virulence factors
3. Virulence lifestyle genes- allow organism to colonize host or reach site of infection

Question 18

MSCRAMMs

Answer 18

-microbial surface components recognizing adhesive matrix molecules- specific proteins which bind to host ligands
>also may be anti-phagocytic by preventing opsonization

**staphs and streps

Question 19

Fimbrae

Answer 19

-help pathogen with attachment

> specific to species (ex. F4 fimbriae in e coli- bind to intestinal epithelium in piglets up to 8wks old vs. F5 fimbriae in e coli- bind to epithelium of distal small intestine of calves during first few days old)

Question 20

Flagella

Answer 20

-Used to reach the site of infection

-Can be used to help determine pathogen (ex. Motility Test)

Question 21

Siderophores

Answer 21

-free iron is a limiting nutrient even in blood
-these chelators allow bacteria to capture Fe3+ in a very low concentration environment

Question 22

Capsule

Answer 22

-polysaccharide structure
-interferes with innate immune system by preventing phagocytosis and attachment of complement
-also protects from bacteriophages

Question 23

Secretion systems

Answer 23

-Structures which transport molecules across the cell envelope

ex. Type 3 secretion system of salmonella used to inject effector molecules into host cells (needle-like!)

Question 24

Toxins

Answer 24

-Wide variety of actions on target receptors/cells/tissues
>includes endotoxins (Lipopolysaccharides) and exotoxins (botulinum toxin, cholera toxin)

Question 25

Superantigens

Answer 25

Antigens which are able to non-specifically bind to and activate the T-cell receptor, resulting in a cytokine storm= massive systemic inflammation, shock, death

Question 26

Enzymes

Answer 26

used by bacteria to break down and invade tissues AND/OR break down molecules for use in their own metabolism

Question 27

Degree of pathogenicity

Answer 27

Non-binary

Accidental pathogen to opportunist facultative to obligate pathogen

Question 28

What effects the degree of pathogenicity

Answer 28

-Whether the organism is pathogenic?

-Is the host susceptible to infection?

-Is the environment permissive to infection?

Question 29

Damage-Response Framework

Answer 29

Spectrum between too little response/overwhelming infection AND too much response/damaging inflammation or allergy
>damage to host is high for either SO want something in the middle between the two

Question 30

Saprophytes examples

Answer 30

1. Rhodococcus equi
   -cause pneumonia in foals, otherwise healthy 12 week olds, most likely due to decline in maternal immunity; also seen in immunocompromised people
2. Aspergillus
   -ubiquitous in nature
   -decomposing matter
   -cause of pneumonia and air sacculitis in birds
   -allergic airway in other horses

Question 31

Opportunistic pathogens

Answer 31

-most clinically relevant organisms
-these pathogens gain access to normally sterile site leading to infection

Question 32

Opportunistic pathogen examples

Answer 32

-Staphylococcus spp= mastitis, UTI, surgical site infections

• Dermatiphilus congolensis= rain scald occurring when wet mascerated skin is traumatized

-E coli (bacteremia/sepsis in most species, UTI)

Question 33

Primary vs secondary infections

Answer 33

-important to look at why a patient has the infection. Is it secondary to another condition?? Or as a result of poor management/environment??

Question 34

Epidemiological triad

Answer 34

1. Environment
2. Susceptible host
3. Virulent agent

Question 35

Environments role on disease

Answer 35

-agent and host need to be in same environment
-favourable conditions
-presence of vectors/reservoirs
-changes that facilitates spread
-change that alters host susceptibility

Question 36

Hosts role in disease

Answer 36

-herd immunity
-individual susceptibility
-nutrition
-co-morbidities
-age

Question 37

Agents role in disease

Answer 37

-possess needed virulence factors
-sufficient numbers
-change in virulence?

Question 38

Zoonosis

Answer 38

An infectious disease caused by a pathogen that has jumped from a non-human animal to a human

*reverse zoonosis- from human to animal

Question 39

When does Koch’s postulates fall short?

Answer 39

-When you are pathogen that cannot be cultured

-one pathogen does not always lead to one disease