4: How to be a Good Pathogen

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Dec 24, 2019
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- 3: Brief History of Infectious Diseases
- 5: Introduction to Bacterial Cell Structure and Antibiotics

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Reading assignment: skim/review chapter 18 in Belk’s Biology p466-477

Vocabulary:

zoonoses
adhesins
reservoir
host receptors
transmission
antibodies
vehicles
toxins
arthropod vectors
enzymes
fomites
pyogenic
portals of entry

To be a good pathogen, one must follow some basic steps: (determinants of infectious disease)

maintain a reservoir
transmission to new host
- enter host->portals of entry
attach to host cells
“outsmart”/evade host defenses
cause damage to host
leave host to find new hosts

1. Maintain a reservoir

3 types of reservoirs

a. humans: ex HIV, cold virus

b. animals

-human diseases caused by pathogens which use animals as a reservoir are called “zoonoses”

-ex rabies, “Bird Flu”

c. environment

water, soil
ex anthrax, fungal infections, cholera

2. Transmission: leave reservoir and find new host (see Belk’s Biology p476-477)

a. Direct: infected host contacts new host and passes pathogen to new host

i. vertical: pathogen passed from mom to baby

ex. HIV, rubella virus, syphilis

ii. horizontal: spread among members of a population

-sexual contact: HIV, HPV, herpes, chlamydia infections

-fluid exchange ex saliva and kissing

ex meningitis, “strept throat”

-bites: rabies

b. Indirect: infected host need NOT be present for pathogen to be passed to new host

-vehicles: water, soil, food

Ex. anthrax, botulism, cholera, polio, prions, hepatitis A

-fomites: inanimate objects contaminated with pathogens

ex smallpox

-blood supplies/donations

ex HIV, hepatitis B/C

-contaminated needles

HIV, hepatitis B/C

-arthropod vectors: West Nile virus, malaria, Lyme Disease

Note: the term “contagious” is defined: a communicable disease that is easily transmitted from a reservoir or patient. (source: Bauman’s Microbiology)

c. “Portals of entry”: how to “get into” host

-broken or damaged skin

- mucous membranes:

gastrointestinal, respiratory, urinary, genital tracts, conjunctiva

-placenta

3. Attaching to host cell

Adhesins: surface molecules on pathogen bind to host receptors
Host receptors: surface molecules on host cells. Pathogen adhesins bind to “complementary” host cell surface receptors (like a lock and key)
Antibodies against pathogen adhesins: antibodies bind to adhesins and block ability of pathogen to bind to host cells, thus stops disease!

4. “Outsmarting”/evading host defenses

a. capsules: prevent phagocytosis by protective host cells

b. toxins (leukocidins) to kill protective cells -triggers “pus” production

pus= fluid containing dead tissue cells, leukocytes and pathogens

-found in abscesses. Pimples, boils and pustules are examples of pus-filled abscesses

-microbes which trigger pus production are called “pyogenic”= pus-makers

- 2 common pyogenic bacterial pathogens are Staphylococcus aureus and Streptococcus pyogenes

c. changing pathogen surface molecules outwits antibodies

d. superantigens “short circuit” immune system

5. Damage to host-a few examples

a. enzymes: examples of some enzymes produced by Staphylococcus aureus

1. enzymes which permit pathogen to invade tissues =hyaluronidase breaks down intercellular “cement” , permits pathogen to spread between cells

2. enzymes which help pathogen “hide” ex coagulase triggers fibrin clot formation around pathogen; camouflage, impedes access of phagocytes

3. enzymes which permit escape from fibrin clots: ex staphylokinase, breakdown fibrin clots, permit spread of pathogen

b. membrane pore-forming substances examples

1. hemolysins lyse red blood cells

2. leukocidins: destroy defensive leukocytes/white blood cells

c. toxins

-example: endotoxins of gram-negative bacteria: trigger circulatory collapse, shock, death

-ex exotoxins such as tetanus, botulinum toxins, diphtheria toxins (disrupt normal cell function)

6. Leave host and find another host!

Study guide How to be a good pathogen

1. What is a “reservoir”?

Provide one specific example of a pathogen which uses each of the following reservoirs

a. humans

b. (non-human) animals

c. environment

2. What is a “zoonosis”? Specific examples?

3. What are “fomites”?

4. What does “transmission” mean?

Describe the following and provide one specific example of a pathogen which is transmitted in the following ways:

direct, contact transmission
indirect transmission
horizontal transmission
vertical transmission

e. arthropod-vector transmission

5. Why is important that a pathogen attach to host cells?

-What do the following terms mean?

a. adhesin

b. host surface receptor

-draw and label a diagram showing how a pathogen may attach to a host cell

6. How can antibodies against pathogen adhesins protect hosts from colonization by a pathogen? Draw and label a diagram to help illustrate your answer.

7. Describe the function of the following microbial virulence factors by filling-in the table:

Virulence factor	function
Hyaluronidase
Coagulase
Staphylokinase
Leukocidins
Hemolysin
Exotoxin
endotoxin

8. What does “pyogenic” mean?

name 2 pyogenic bacterial pathogens.
what is “pus”?
what are: abscesses, pimples, pustules, boils?

9. How can pathogens evade/avoid defenses/immune responses of the host?

Contributors

Karen Carberry-Goh, D.V.M., Ph.D. (Sacramento City College)

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Study guide How to be a good pathogen

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