Host-Pathogen Interactions

Exam 1 - Lec 1

What is an obligate pathogen?

always pathogenic

What is a commensal organism?

a pathogen that is potentially or never pathogenic

Most microbes are _______ pathogenic.

never → ex: yeast

What environmental factors can influence pathogenicity?

season, rain, vectors

What microbial characteristics can influence pathogenicity?

virulence, bacterial loads, toxins

What host factors can influence pathogenicity?

genetics, susceptible/resistant, immune status, age, nutrition, stress

What is the overall pathway of a pathogenic infection?

entry → adherence → invasion → colonization → growth

Health and disease is a race between a ____________ and the ___________.

pathogen trying to gain a foothold

host defenses trying to prevent the pathogen from doing so

Health is the balance between _________ and _____.

normal microbiota

host

Disease is imbalance between ______ and __________.

immune system

normal microbiota overwhelmed by pathogens

What are Koch’s 4 postulates?

1. Same pathogen must be present in every case of the disease

2. Pathogen must be isolated in pure culture

3. Pathogen isolated from pure culture must cause the same disease in lab animal

4. Pathogen must be re-isolated from inoculated lab animal

T/F: The host is a uniform environment.

FALSE - is NOT

T/F: Bacterial flora is different in different locations.

TRUE - Staph a (skin), Mycobacterium (lung), Clostridium (intestinal tract)

Mutualism or symbiosis

bacteria and host are benefited (rumen bacteria)

Commensalism

bacteria are benefited and host is “unaffected” - commensals - normal flora

Parasitism

bacteria are benefited and the host is harmed (parasite)

Normal flora is present on the _____ and ___________.

skin

mucous membranes

Bacterial antagonism

protective function against pathogens

How does bacterial antagonism work?

compete for attachment

compete for nutrients

produce substances that inhibit pathogens

Probiotics are considered

competitive exclusion

T/F: Germ-free hosts are more healthy than hosts with normal microbiota.

FALSE - less healthy

Pathogenesis

the process & mechanisms of the disease development

Pathogenecity

capacity/ potential of an organism to cause the disease

Virulence

relative pathogenicity (LD₅₀, ID₅₀)

Invasiveness

the ability to enter, survive, multiply, and spread in the host

LD₅₀ - lethal dose

the # of microbes in a dose that will kill 50% of inoculated test animals

ID₅₀ - infectious dose

the dose required to produce a demonstratable infection in 50% of the test animals

Frank (true) pathogen

cause disease in normal hosts → obligate pathogen

Opportunistic pathogen

causes disease only when conditions are favorable

Extracellular pathogen

grows and multiplies in the space and fluids surrounding the cells

Intracellular pathogen

grows and multiplies inside the cells

Facultative intracellular pathogen

grows and multiplies inside and outside cells → can be cultured in bacteriological media

a lot of pathogens are in this category

Obligate intracellular pathogen

grows and multiplies only inside cells → only can be cultured in the lab in tissue culture media