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Medical Microbiology > Section 1- Microbial Pathogenesis > Flashcards

Section 1- Microbial Pathogenesis Flashcards

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1
Q

2 main contributors to Germ Theory of Disease

A

Louis Pasteur (France) and Robert Koch (Germany)

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2
Q

Louis Pasteur

A

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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3
Q

Robert Koch

A

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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4
Q

Koch’s Postulates

A
  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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5
Q

Exceptions to Koch’s postulates (3)

A

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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6
Q

3 types of microbe-host relationships

A

Mutualism
Commensalism
Parasitism

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7
Q

Mutualism

A

Both species benefit from the association

Ex: E. coli in human intestinal tract

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8
Q

Commensalism

A

One species benefits without harming the other

Ex: Staphylococcus epidermis on human skin

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9
Q

Parasitism

A

One species derives benefit while damaging its host

Ex: Mycobacterium tuberculosis

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10
Q

Pathogen

A

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

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11
Q

Colonization

A

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

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12
Q

Infection

A

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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13
Q

Acute infection

A

Symptoms develop rapidly

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14
Q

Chronic infection

A

Symptoms develop slowly and are resolved over months

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15
Q

Latent infection

A

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

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16
Q

Disease

A

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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17
Q

Nosocomial infections

A

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

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18
Q

Exogenous infection

A

Pathogen acquired within the health care environment

From bedding, clothing, other patients, etc.

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19
Q

Iatrogenic infection

A

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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20
Q

Pathogenicity

A

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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21
Q

Normal microbiota

A

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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22
Q

Primary pathogens

A

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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23
Q

Opportunistic pathogens

A

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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24
Q

Virulence

A

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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25
Q

How is virulence estimated?

A

Median Infectious Dose (ID50)

Quantitative measure

26
Q

Median Infectious Dose (ID50)

A

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

27
Q

Median lethal dose (LD50)

A

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

28
Q

Sign

A

Something that can be observed by a person examing a patient

Ex: Fever, cough, rash, etc.

29
Q

Symptom

A

Something that can be felt only by the patient

Ex: pain, malaise, fatigue

30
Q

Syndrome

A

Collection of signs and symptoms that accompany a specific disease

31
Q

Post-infectious sequelae

A

Pathologic consequences occurring even after the infection has been eradicated
Ex: immune system continues to react

32
Q

Stages of Infectious Disease

A 
Incubation phase
Prodromal phase
Illness phase
Decline phase
Convalescent phase
Long term
33
Q

Incubation phase

A

Pathogen begins to colonize host
Low number of microbes
Low immune response

34
Q

Prodromal phase

A

Pathogen replicates and 1st (nonspecific) signs/symptoms begin
Innate immune system responds
Moderate number of microbes
Relatively low immune response

35
Q

Illness phase

A

Innate immune system fails
Adaptive immunes response
High number of microbes
Moderate immune response

36
Q

Decline phase

A

Signs/symptoms wane
Immune system fully activated
Moderate number of microbes
High immune response

37
Q

Convalescent phase

A

Signs/symptoms gone
Immune system still active
Low number of microbes
Immune response remains high

38
Q

Long term

A

Immunological memory
Very low level of microbes
Moderate immune response

39
Q

Stages of pathogenesis

A 
Transmission/Exposure
Portals of Entry
Adherence/Colonization/Infection--> Immune Evasion
Invasion OR Toxicity
Nutrient Acquisition
Clinical Disease
Dissemination
40
Q

2 primary modes of transmission

A

Direct and Indirect

41
Q

Direct Transmission

A

Microbes can be transmitted by direct contact or aerosols

42
Q

Indirect Transmission

A

Simplest mode

Microbes can be transmitted by inanimate objects (fomites), by vehicle transmission, or by a biological vector

43
Q

Vehicle trasmission

A

Microbes transmitted indirectly through fomites, food, water, air, etc.

44
Q

Vector

A

Organism with ability to transmit pathogen from one host organism to another

45
Q

Vertical transmission

A

Less common

Microbes can be transmitted from mother to baby either during development or shortly after birth

46
Q

Reservoirs of infection

A

Habitats in which a pathogen can survive and/or multiply
Necessary to ensure the pathogen can be transmitted to a new host
3 types: Animal, Human carriers, Nonliving

47
Q

Animal reservoirs

A

Zoonotic diseases
Zoonoses=diseases that are naturally spread from their usual animal host to humans
Ex: Bubonic plague

48
Q

Human carriers

A

Infected individuals who are asymptomatic (sub-clinical) but can transmit the pathogen to new individuals
Unaware of infection

49
Q

Nonliving reservoirs

A

Soil, water, food, etc

Presence of microorganisms often due to contamination by feces or urine

50
Q

Portal of entry

A

Route a pathogen takes to enter a host

Eye, Respiratory, Parenteral (bloodstream), Oral, Skin, Genital or sexual

51
Q

Pathogens that cross the placenta

A

Vertical transmission
Placenta typically forms an effective barrier to bacterial/viral pathogens as the two blood supplies are not in physical contact
Ex: Syphilis, AIDS, toxoplasmosis

52
Q

Virulence factors

A

Genetically encoded traits that allow the microbe to cause disease; contribute to multiple aspects of pathogenesis
Ex: colonization, immune evasion, nutrient acquisition, dissemination
Environmental persistence (spore formation)
Transmission (resistance to desiccation, etc.)
Adherence (production of adhesins)
Immune evasion (multiple strategies)
Tissue damage (Endotoxins, exotoxins, secreted enzymes, etc.)
Dissemination (Exit from host)
*Pathogen must have 1 or more of these to cause disease

53
Q

Surface virulence factors

A

Capsules (adherence, immune evasion)
Fimbriae (adherence, immune evasion)
Flagella (motility, tissue invasion)

54
Q

Endotoxin

A 
Lipopolysaccharide (LPS)
Component of outer membrane
Humans very sensitive
Leads to inflammatory responses (tissue/organ damage)
Gram (-) only
Death due to endotoxic shock
55
Q

Exotoxins

A

Released from bacteria and affect distal body sites
Majority are PROTEINS released by the pathogen
Tissue damage and nutrient release
Dissemination to new hosts
Immune evasion

56
Q

Meningitis Surface Virulence Factors

A

3 major pathogens responsible for this disease
Streptococcus pneumoniae
Neisseria meningitidis
Haemophilus influenzae
All share common virulence factor- polysaccharide capsule

57
Q

Portals of exit (Dissemination)

A 
Ear (ear wax)
Broken skin (blood)
Skin (flakes)
Anus (feces)
Seminal vesicles (semen and lubricating secretions)
Urethra (urine)
Vagina (secretions, blood)
Mammary glands (milk, secretions)
Mouth (saliva, sputum)
Nose (secretions)
Eyes (tears)
58
Q

Epidemiology

A

Study of where and when diseases occur and how they are transmitted within populations
4 types of disease: Endemic, Sporadic, Epidemic, Pandemic

59
Q

Sporadic disease

A

Rare, isolated
Only a few scattered cases occur within a given area or population
Cause not always identified
Ex: diptheria in U.S. (still endemic in other parts of world)

60
Q

Endemic disease

A

Normally occurs at a relatively stable incidence within a given population or area
Number of annual cases can be LOW (10s) or very HIGH (few million)
Ex: influenza in the US
Ex: human plague (~10 cases/year)

61
Q

Epidemic disease

A

Occurs when a disease exceeds its normal frequency within a given population
May start endemic
Ex: Every 10-15 years the US has an epidemic outbreak of influenza

62
Q

Pandemic disease

A

Occurs when an epidemic outbreak spreads across continental barriers
Ex: ZIKA Virus
Started endemic in a small island nation and then spread

Medical Microbiology (5 decks)

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