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Medical Microbiology > Section 1- Microbial Pathogenesis > Flashcards

Section 1- Microbial Pathogenesis Flashcards

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
How is virulence estimated?
Median Infectious Dose (ID50) | Quantitative measure
26
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
27
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
28
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
30
Syndrome
Collection of signs and symptoms that accompany a specific disease
31
Post-infectious sequelae
Pathologic consequences occurring even after the infection has been eradicated Ex: immune system continues to react
32
Stages of Infectious Disease
``` Incubation phase Prodromal phase Illness phase Decline phase Convalescent phase Long term ```
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Incubation phase
Pathogen begins to colonize host Low number of microbes Low immune response
34
Prodromal phase
Pathogen replicates and 1st (nonspecific) signs/symptoms begin Innate immune system responds Moderate number of microbes Relatively low immune response
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Illness phase
Innate immune system fails Adaptive immunes response High number of microbes Moderate immune response
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Decline phase
Signs/symptoms wane Immune system fully activated Moderate number of microbes High immune response
37
Convalescent phase
Signs/symptoms gone Immune system still active Low number of microbes Immune response remains high
38
Long term
Immunological memory Very low level of microbes Moderate immune response
39
Stages of pathogenesis
``` Transmission/Exposure Portals of Entry Adherence/Colonization/Infection--> Immune Evasion Invasion OR Toxicity Nutrient Acquisition Clinical Disease Dissemination ```
40
2 primary modes of transmission
Direct and Indirect
41
Direct Transmission
Microbes can be transmitted by direct contact or aerosols
42
Indirect Transmission
Simplest mode | Microbes can be transmitted by inanimate objects (fomites), by vehicle transmission, or by a biological vector
43
Vehicle trasmission
Microbes transmitted indirectly through fomites, food, water, air, etc.
44
Vector
Organism with ability to transmit pathogen from one host organism to another
45
Vertical transmission
Less common | Microbes can be transmitted from mother to baby either during development or shortly after birth
46
Reservoirs of infection
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
Animal reservoirs
Zoonotic diseases Zoonoses=diseases that are naturally spread from their usual animal host to humans Ex: Bubonic plague
48
Human carriers
Infected individuals who are asymptomatic (sub-clinical) but can transmit the pathogen to new individuals Unaware of infection
49
Nonliving reservoirs
Soil, water, food, etc | Presence of microorganisms often due to contamination by feces or urine
50
Portal of entry
Route a pathogen takes to enter a host | Eye, Respiratory, Parenteral (bloodstream), Oral, Skin, Genital or sexual
51
Pathogens that cross the placenta
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
Virulence factors
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
Surface virulence factors
Capsules (adherence, immune evasion) Fimbriae (adherence, immune evasion) Flagella (motility, tissue invasion)
54
Endotoxin
``` Lipopolysaccharide (LPS) Component of outer membrane Humans very sensitive Leads to inflammatory responses (tissue/organ damage) Gram (-) only Death due to endotoxic shock ```
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Exotoxins
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
Meningitis Surface Virulence Factors
3 major pathogens responsible for this disease Streptococcus pneumoniae Neisseria meningitidis Haemophilus influenzae All share common virulence factor- polysaccharide capsule
57
Portals of exit (Dissemination)
``` 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
Epidemiology
Study of where and when diseases occur and how they are transmitted within populations 4 types of disease: Endemic, Sporadic, Epidemic, Pandemic
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Sporadic disease
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
Endemic disease
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
Epidemic disease
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
Pandemic disease
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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