Pathogenicity and Infection Flashcards
(104 cards)
1
Q
What is a host?
A
A larger organism that supports that survival and growth of a pathogenic microorganism.
2
Q
What is an infection?
A
A microbe growing and multiplying on or within a host. May or may not result in overt disease.
3
Q
What is an infectious disease?
A
Any changes from a state of health that occurs when part or all of the host is incapable of carrying on normal functions due to the presence of a pathogen or its products.
4
Q
What is a pathogen?
A
Any organism that causes disease.
5
Q
What is a primary pathogen?
A
Causes disease by direct interaction with a healthy host.
6
Q
What is a opportunistic pathogen?
A
May be part of the normal microbiota and causes disease when the host is immunocompromised.
7
Q
What is pathogenicity?
A
Ability of a pathogen to cause disease.
8
Q
What is virulence?
A
Degree of harm/pathogenicity inflicted on its host.
9
Q
What are extracellular pathogens?
A
Pathogens that remain in tissues and/or fluids but never enter host cells during disease.
10
Q
What is an intracellular pathogen?
A
Pathogens that grow and multiply within host cells.
11
Q
What are the 2 types of intracellular pathogens?
A
- Facultative intracellular pathogens.
- Obligate intracellular pathogens.
12
Q
What are facultative intracellular pathogens?
A
Intracellular pathogens that can also grow and multiply in a pure culture w/o host cell support.
13
Q
What are obligate intracellular pathogens?
A
Intracellular pathogens that can only grow inside host cells.
14
Q
What are signs, in the context of pathogenicity and infection?
A
Objective changes that can be directly observed and measured.
ex: Fever, rash, swelling.
15
Q
What are symptoms?
A
Subjective changes.
ex: Pain, loss of appetite, level of exhaustion.
16
Q
What is a disease syndrome?
A
A set of characteristic signs and symptoms for a disease.
ex: Coughing, sneezing, sore throat, fever, green mucus, swollen lymph nodes, mouth sores.
17
Q
What 3 things does the host provide the pathogen with?
A
- Protection.
- Energy to use.
- Nutrients.
18
Q
What factors impact the success of transmission?
A
- Number of invading organisms.
- Virulence of organism.
- Presence of adhesion and invasion factors.
19
Q
What must a pathogen do in order to survive in the body?
A
- Outcompete the resident microbiota for resources.
- Survive host defense mechanisms.
20
Q
When does disease ensue in an organism?
A
When the organism produces molecules that directly damage host cells or stimulate host immune cells to destroy infected tissue.
21
Q
What are the 4 stages of disease progression?
A
- Incubation period.
- Prodromal period.
- Illness period.
- Convalescence or Death.
22
Q
When does the incubation period occur?
A
From pathogen entry to development of signs and symptoms.
23
Q
What occurs during the prodromal stage?
A
Mild, non-specific signs and symptoms.
24
Q
What occurs during the illness period?
A
The disease is at its most severe and definitive signs and symptoms are displayed.
25
What occurs during convalescence?
The organism recovers from the illness.
*Alternatively, the organisms could also unfortunately succumb to the illness.
26
What are animate sources of pathogens?
1. Animals.
2. Humans
27
What are inanimate sources of pathogens?
1. Water.
2. Food.
28
What is a reservoir?
A natural environmental location in which the pathogen normally resides.
29
What is a vector?
An organism that spreads disease from one host to another.
ex: Mosquitoes, fleas, ticks, biting flies, mites.
30
What are the 5 main routes of transmission?
1. Airborne.
2. Contact.
3. Vehicle.
4. Vector-borne.
5. Vertical transmission.
31
What does the efficiency of transmission increase with?
Extensive multiplication.
32
What is a pathogen's virulence influenced by?
Its ability to live outside its host.
33
Exposure alone is not enough for infection to occur, tropism must be present as well. What is tropism?
The pathogen must be in contact with the appropriate host tissue.
ex: A respiratory virus may not cause an infection if it lands on a foot.
34
What is tropism determined by?
Specific cell surface receptors.
35
What are the three forms of airborne transmission?
1. Droplets.
2. Droplet nuclei.
36
Which form of airborne transmission is direct?
Droplet.
37
What are the characteristics of droplet transmission?
1. Droplets up to 2mm in diameter.
2. Produced when a liquid is under force (ex: saliva, mucus).
3. Can travel <1m.
38
Which forms of airborne transmission is indirect?
1. Droplet nuclei.
2. Dust particles.
39
What are the characteristics of droplet nuclei transmission?
1. Droplets 1-5 um in diameter.
2. Results from evaporation of larger droplets.
3. May remain airborne for hours or days.
4. Can travel across long distances.
40
What are the characteristics of dust particles?
1. Aerosolized, smaller than 1 um.
2. Can be dispersed farther.
3. Microorganisms can adhere to dust particles.
4. Allows for hospital acquired infections due to long survival time outside of host (s).
41
How does contact transmission occur?
The host touching the source or reservoir of the pathogen.
42
What are the 2 forms of contact?
1. Direct.
2. Indirect.
43
What is direct contact?
Physical interaction with the host.
ex: Touching or sexual contact.
44
What is indirect contact?
A fomite that transfers the infectious agent between hosts.
45
How does vehicle transmission occur?
When a fomite contacted by an infectious host is contacted by 1 or more uninfected animals, further spreading the infection.
ex: Surgical instruments, drinking water, food, biological material, air.
46
What is vector-borne transmission?
A living organism that can transmit a pathogen.
ex: Insects, mites, ticks, fleas, dogs, cats, bats, skunks.
47
How do pathogens benefit from the vector-borne transmission method?
1. Extensive reproduction.
2. Extensive spread between hosts.
*Pathogen does not normally harm the vector.
48
What are the 2 types of vector-borne transmission?
1. External/mechanical.
2. Internal.
49
What is external/mechanical transmission?
Passive carriage of the pathogen on the body of the vector with no growth of the pathogen during transmission.
ex: A bacteria that lives on the vectors skin.
50
What is internal transmission?
When the pathogen is carried within the vector and transmitted by exposure to bodily fluids.
51
What are the 2 sub-categories of internal transmission?
1. Harborage transmission.
2. Biologic transmission.
52
What occurs during harborage transmission?
Pathogen does NOT undergo changes within the vector.
53
What occurs during biologic transmission?
Pathogen DOES undergo changes within the vector.
54
What is vertical transmission?
When the unborn child acquires a pathogen from an infected mother across the placenta.
*Not as common as horizontal transmission.
55
What are the infected fetuses said to have as a result of the vertically transmitted infection?
A congenital infection.
56
What is infectious dose 50 (ID_50)?
The number of microbes required to cause disease in 50% of inoculated hosts.
57
What is lethal dose 50 (LD_50)?
The pathogen dose that kills 50% of a group of experimental hosts within a specified period.
58
What is LD_50 influenced by?
Susceptibility to infection.
59
What 4 factors influence susceptibility of the host?
1. Immune system strength.
2. Cleanliness/Hygiene.
3. Nutrition.
4. Emotional health.
60
What is the first step in an infection?
Entry and adherence to establish colonization of the host using portals of entry.
61
What are portals of entry?
Portions of the body that pathogens could potentially use to gain further access to the rest of the body.
ex: Skin, respiratory tract, gastrointestinal tract, urogenital system, conjunctiva of the eye.
62
What defenses does the skin have to prevent pathogen infiltration?
1. Is a strong mechanical barrier.
2. Consistently sheds its outermost layer.
3. Slightly acidic pH.
4. High NaCL concentration (from sweat).
5. Subject to periodic drying.
*Keratin aids in this protection.
63
What defenses do the mucous membranes have to prevent pathogen infiltration?
1. Forms a protective covering over many body surfaces to resist penetration and trap microbes for later destruction by the immune system.
2. Lysozymes (hydrolyzes bonds between sugars in peptidoglycan).
3. Lactoperoxidase: Produces superoxide radicals.
4. Lactoferrin: Binds iron more tightly than bacterial proteins, hindering the success of bacterial infections.
64
What defenses does respiratory system have to prevent pathogen infiltration?
1. Mucus coated surfaces that trap microbes that are then expelled through coughing and/or sneezing.
2. Saliva washes microbes in the mouth to the stomach.
3. Alveolar macrophages destroy bacteria in the alveoli.
65
What defenses do the eyes have to prevent pathogen infiltration?
1. The flushing action of tears.
2. A mucus secreting epithelial membrane.
3. Lysozymes.
4. Lactoferrin.
5. Secretory IgA.
66
What defenses does the gastrointestinal tract have to prevent pathogen infiltration?
1. Gastric acid (stomach).
2. Pancreatic enzymes (SI).
3. Bile (SI).
4. Intestinal enzymes (SI).
5. Peristalsis (SI).
6. Shedding of columnar epithelium cells.
7. Secretory IgA.
8. Normal microbiota.
67
What defenses does the urinogenital tract have to prevent pathogen infiltration?
1. Low pH of urine.
2. Low pH in vagina.
3. Urea and other toxic metabolic products
4. Vagina contains lactobacilli.
5. Distance barrier in male trace.
6. Flushing with mucus and urine.
68
What is colonization?
Establishment of a site of microbial replication on or without a host.
69
What structures can be categorized as adherence structures?
1. Fimbriae.
2. Pili.
3. Specialized adhesion molecules on a microbe's cell surface.
4. Membrane and capsular materials.
70
What is infectivity?
The ability to create a discrete point of infection.
ex: A lesion on the skin.
71
What is invasiveness?
Th ability to spread to adjacent tissues.
72
What are the two ways pathogenic penetration can be categorized?
1. Active.
2. Passive.
73
What is active penetration?
The pathogen produces lytic substances that alter host tissue.
74
In what ways do the lytic substances alter the host tissues?
1. Attack the ECM and basement membranes of the integument and intestinal lining.
2. Disrupt host-cell surface.
3. Degrade the carbohydrate-protein complexes between cells.
75
What is passive penetration?
When the penetration occurs due to something indirectly related to the pathogen.
ex: A cut that allows bacteria on the skin to enter the bloodstream.
76
What is bacteremia?
The presence of viable bacteria in the blood.
ex:
77
What is septicemia?
The presence of bacterial of fungal toxins in the blood.
ex: Clostridium tetani.
78
Can an organism cause both bacteremia and septicemia?
1. Bacillus anthracis.
2. Yersinia pestis.
79
What unique method of invasion does L.monocytogenes, Rickettsia spp., and Shigella spp. use to invade host cells?
Bacterial cell surface proteins to polymerize actin on the host cell, turning it into a propellor, propelling the bacteria to be engulfed by the host cell.
*Evades the immune response.
80
What happens to most microbes before they can cause disease?
They are eliminated from the immune system.
81
What strategies do successful pathogens use to evade the innate and adaptive immune systems?
1. Produce a Type IV secretion system.
2. Excrete specialized proteins to selectively kill host cells.
3. Find shelter to avoid recognition by defense cells.
4. Produce enzymes that inactivate innate resistance mechanisms.
5. Survive and replicate inside host cells.
6. Secrete exopolysaccharides to form communal shelters within biofilms.
7. Squeeze between host cells.
8. Burrow under mucus.
9. Make capsule to avoid phagocytosis.
10. Cause host cell fusion to spread without exposure to immune system.
11. Production pf decoy proteins to bind antimicrobial proteins.
12. Produce special proteins that interfere with the host's ability to detect and remove the pathogen.
13. Mutate the cell surface proteins.
14. Produce proteases that degrade host proteins.
15. Reduce the number of cell surface proteins.
16. Switching of genes that encode similar proteins due to phages (phage variation).
82
What is an example of phage variation?
Alteration pili protein sequence and expression.
83
What is a pathogenicity island?
A large segment of bacterial chromosomal and plasmid DNA found to encode virulence factors.
84
How big is a pathogenicity island?
10-200 kilobases.
85
What do pathogenicity islands result in?
Increased bacterial virulence.
86
What kind of bacteria are pathogenicity islands absent in?
Non-pathogenic organisms, even within the same genus or species.
87
How do pathogens suppress the host immune response?
1. Infect immune cells and diminish their function.
2. Some (ex: Strep.pneumoniae) produce a slippery mucoid capsule that prevents phagocytosis by host immune cells.
3. Eliminate the O-antigen on the LPS to diminish immune recognition and clearance.
88
What is a toxin?
A substance that disrupts the normal metabolism of host cells.
89
What is toxigenicity?
A pathogen's ability to produce toxins.
90
What are intoxicants?
Disease(s) that result from the entry of a specific toxin into a host.
*No actively growing pathogen needed.
91
What are exotoxins?
Soluble, heat-liable proteins released from a bacteria that causes disease in hosts.
92
How do exotoxins impact the body?
They travel from the site of infection to other tissues or target cells, where they exert their effect.
93
What encodes exotoxins?
1. Genes on a plasmid.
2. Genes in a prophage within a bacteria.
94
What are the 2 types of exotoxin?
1. AB toxin.
2. Superantigen.
95
What is the function of the A subunit of the AB toxin?
Catalyzes the reaction that causes toxicity.
96
What kind of exotoxin is AB toxin?
Host site specific.
97
What does AB toxin do to the host cell membrane?
Destabilizes it.
98
What do superantigens stimulate?
30% of host T cells.
99
What does superantigen cause host T cells to do?
Overexpress genes that encode cytokines and release pro-inflammatory molecules.
100
What does superantigen stimulation of T cells ultimately result in?
Multiple organ failure, allowing for the microbe to disseminate.
101
What are the general features endotoxins?
1. Toxic (nanogram amounts).
2. Heat stable.
3. Causes fever, shock, blood vessel damage, weakness, inflammation, diarrhea, intestinal hemorrhage, and fibrinolysis.
102
What is a common example of an endotoxin?
LPS, specifically the Lipid A portion.
103
What are mycotoxins?
Toxins produced by fungi.
ex: Aspergillus flavus.
104
Where can mycotoxins be found?
1. Contaminated crops.
2. Water damaged buildings.
3. Drugs (LSD is a byproduct of fungi).
