Section 1- Microbial Pathogenesis Flashcards Preview

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Flashcards in Section 1- Microbial Pathogenesis Deck (62)
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1

2 main contributors to Germ Theory of Disease

Louis Pasteur (France) and Robert Koch (Germany)

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Louis Pasteur

2 big contributions:
Used swan-neck flask to show that bacteria are not the result of spontaneous generation
Shows that certain organisms can grow anaerobically

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Robert Koch

3 big contributions:
Develops solid growth media, which allows pure culture of bacteria
Demonstrates principle of disease transmission in rabbits with anthrax
Applies scientific method to study of infection (Postulates)

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Koch's Postulates

1. Suspected microbe must be observed in all cases of the disease (OBSERVE)
2. Suspected microbe must be isolated and grown in pure culture (ISOLATE)
3. Isolated microbe must cause the same disease when inoculated into a healthy animal (INOCULATE)
4. Same microbe must be recovered from the newly infected animal (RECOVER)

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Exceptions to Koch's postulates (3)

Some pathogens cannot be grown in pure culture (Mycobacterium leprae and viral agents)
Some diseases caused by a combo of pathogens (Atrophic rhinitis)
Applying Koch's postulates to human specific pathogens may be unethical (HIV, Leprosy)
*Molecular techniques have overcome some of these limitations (HIV and PCR)

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3 types of microbe-host relationships

Mutualism
Commensalism
Parasitism

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Mutualism

Both species benefit from the association
Ex: E. coli in human intestinal tract

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Commensalism

One species benefits without harming the other
Ex: Staphylococcus epidermis on human skin

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Parasitism

One species derives benefit while damaging its host
Ex: Mycobacterium tuberculosis

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Pathogen

Any bacterium, virus, fungus, protozoan, or helminth (worm) that causes disease

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Colonization

Ability of a microbe to adhere to a body surface and replicate
Encompasses all types of symbiotic relationships

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Infection

Invasion by and multiplication of a pathogen in a bodily part or tissue
MAY lead to overt clinical disease
Acute, chronic, or latent

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Acute infection

Symptoms develop rapidly

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Chronic infection

Symptoms develop slowly and are resolved over months

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Latent infection

Persists after an acute illness
Organisms are present, but disease is not
Ex: happens in over 95% of Tb patients

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Disease

A disorder of the normal structure or function of any body part, organ, or system, especially one that produces specific signs or symptoms

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Nosocomial infections

Infections acquired while in a health care-associated facility (retirement home, hospital, etc.)
Exogenous or Iatrogenic

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Exogenous infection

Pathogen acquired within the health care environment
From bedding, clothing, other patients, etc.

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Iatrogenic infection

Consequence of direct medical intervention
Ex: Administration of drugs (disrupt microbiota, immune system suppression), Insertion of medical devices (shunts, IV lines, catheters)
Organisms often highly virulent, highly antibiotic resistant

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Pathogenicity

Ability of a microbe to cause disease within a host
Product of several determinants:
Host range (one or many hosts)
Portal of entry (body site)
Virulence factors
Host factors (Genetics, immune status, etc.)

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Normal microbiota

Body colonized by numerous mutualistic and commensal symbionts
Many organisms beneficial (ex: E. coli produce vitamin K, a blood clotting factor)

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Primary pathogens

Capable of causing disease in healthy animals
Ex: Mycobacterium tuburculosis, Neisseria gonorrheae
Can be prevented by immunization
Responsible for significant morbidity and mortality in the developing world
Largely controlled in developed countries

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Opportunistic pathogens

Low probability of causing disease in healthy individuals
Increased probability of causing disease in immunocompromised individuals
Responsible for high morbidity and mortality in the developed world

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Virulence

The relative ability of a microbe to cause disease within the same host
The virulence of individual strains within a species can vary (ex: E. coli)
High virulence=high probability of causing disease

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How is virulence estimated?

Median Infectious Dose (ID50)
Quantitative measure

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Median Infectious Dose (ID50)

Number of microorganisms required to cause an infection in half the members of a tested population
Low ID50=highly infectious (ex: Shigella)
High ID50= moderately infectious (ex: E. coli)
Summary- higher number of organisms= higher likelihood of disease

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Median lethal dose (LD50)

Number of microorganisms required to kill half the members of a tested population
ID50 and LD50 for a given pathogen can vary significantly
Infectious dose ALWAYS lower than Lethal dose

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Sign

Something that can be observed by a person examing a patient
Ex: Fever, cough, rash, etc.

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Symptom

Something that can be felt only by the patient
Ex: pain, malaise, fatigue

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Syndrome

Collection of signs and symptoms that accompany a specific disease