Interaction Between Microbe and Host
Principles of Disease and Epidemiology (parts of Ch. 14)
I will not be discussing this chapter in class but you are being held responsible to know the
information in Chapter 14 that is on this handout.
Host Microbe Interactions: Several forms of symbiosis (Living together)
Mutalism- beneficial to both
Commensalism- One organism benefits, other is unaffected
Parasitism- beneficial to one, harmful to the other
Biofilms!!!
Most interactions with microbes are beneficial or neutral to the human
Normal microbiota- important for our health
Vitamins
Aid with food digestion
Necessary for developing immune system
Keeps pathogenic and opportunistic species numbers low
Microbial antagonism and competitive exclusion
One example: E. coli-Bacteriocins
Probiotics: Live cultures taken internally or applied
A few interactions are harmful and cause disease (parasitism): Some important terminology
Pathology- study of diseases
Etiology- cause of diseases
Pathogenesis- development of a disease
Infection- invasion or colonization of the body by pathogenic micro-organisms
Disease- change in the state of health
Opportunistic Organisms: relationship between host and microbe changes because:
The microbe(s) are not in their “normal” habitat:
Host is already compromised:
Normal microbiota is eliminated or changed:
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Etiology of Infectious Diseases
Koch’s postulates
1. same pathogen present in every case of the disease
2. pathogen must be isolated and grown in pure culture
3.pathogen must cause the disease when inoculated into its host
4. the pathogen must be re-isolated from the inoculated host
Exceptions and Problems with Koch’s Postulates:
Not all causative agents can be cultured on artificial media
Some agents cause various diseases, and vice-versa
Only has human host???? Hard to find the volunteers!
Predisposing Factors for disease:
Genetics, climate, weather, state of health/nutrition…..
The Spread of Infection
Reservoirs of Infection- need a continual source of disease organisms
Human
Animal
Nonliving
Transmission of Disease- from reservoir to a susceptible host
Contact
Direct
Indirect
Droplet
Vehicle
Water, food, air
Vectors- carry pathogen from one host to another
Arthropods (mosquitoes, ticks, fleas, etc.)
Mechanical transmission- typhoid fever
Biological transmission-malaria
Nosocomial (Hospital-Acquired) Infections:
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