Lecture 20 General Microbiology Flashcards
1
Q
What is pathogenicity?
A
- Ability to produce pathological change or disease
- Pathogen: any disease-producing microorganism.
2
Q
What are gnotobiotic animals?
A
- All microbial species present are known.
- Germ-free
- Used to study interactions of aimals and specific microogranisms
- Only certain known strains of bacteria and other microorganisms are present.
3
Q
How do you establish gnotobiotic animal colonies in mammals?
A
- Free of microbes in utero
- Established by caesarean-section delivery in germfree isolate
- Maintain in sterile environment
- Normal mating and delivery of gnotobiotic mammals maintains colony
4
Q
How do you establish gnotobiotic animal colonies in BIRDS?
A
- Germicide treatment of fertile eggs
- Hatch eggs in sterile isolators
5
Q
What are the characteristics of gnotobiotic animals?
A
- More susceptible to pathogens, except those cause by protozoa that use gut bacteria as food source
- Does not carry any pathogen load
6
Q
What is normal microbiota? What is ectosymbiosis? What is endosymbiosis?
A
Normal microbiota: microbes regularly found at a site
Ectosymbiosis: one organism remains outside of the other
Endosymbiosis: one organism is present within the other
7
Q
Why is it important to study normal huma microbiota?
A
- To gain insight into possible infections resulting from injury
- To understand causes and consequences of overgrowth of microbes normally absent from a body site
- To increase awareness of role played by indigenous microbe in stimulating immune response
8
Q
What makes our skin so awesome?
A
- Has both resident microbiota and transient microbiota
- Mechanically strong barrier
- Keratin intractable to micriobial attack
- Most areas subject to periodic drying
- Slightly acidic
- Salty
- Inhibitory substances (e.g., lysozymes)
9
Q
Describe what leads up to acne vulgaris.
A
- Causes in part by activities of Propionibacterium acnes.
-
Sebum: fluid secreted by oil glands.
- Accumulates, providig hospitable environment for P. acnes
-
Comedo: plug of sebum and keratin in duct of oil gland
- Results from inflammatory response to sebum accumulation.
10
Q
How are the microbes in the respiratory tract?
A
- No normal microbiota
- Microbes moved by:
- Continuous stream of mucous generated by ciliated epithelial cells
- Phagocytic action of alveolar macrophages
- Lysozyme in mucus
11
Q
How are the microbes in the mouth??
A
- Contains organisms that survive mechanical removal by adhering to gums and teeth
- Contribute to formation of dental plaque, dental caries, gingivitis, and periodontal disease.
12
Q
How are the microbes found in the stomach and small intestine???
A
- Most microbes killed by acidic conditions
- Some survive if passed through stomach very quickly.
- Some can survive if ingested in food particles
13
Q
How are the microbes in the large intestine (colon)?
A
- Largest microbial population of body
- Eliminated from body by peristalsis, desquamation, and movement of mucus.
- Replaced rapdily because of their high reproductive rate.
14
Q
What is the microbiota like in the Genitourinary tract?
A
- Kidneys, ureter, and bladder
- Normally free of microbes
- Distal portions of urethra
- Few microbes found
- Female genital tract
- Complex microbiota in a state of flux due to menstrual cycle
- Acid-tolerant lactobacilli predominate
15
Q
Describe the various relationship normal microbiota and the host can experience.
A
- Usually mutually beneficial
- Normal microbiota often prevent colonization by pathogens
- Opportunistic pathogens: members of normal microbiota that produce disease under certain circumstances
- Compromised host: debilitated host with lowered resistance to infection.
16
Q
Describe the overview of what is involved in host resistance to a pathogen.
A
-
Immune system: recognizes foreign substances or microbes and acts to neutralize or destroy them.
- Composed of widely distributed cells, tissues, and organs.
- Immunity: ability of host to resist a particular disease or infection
- Immunology: science concerned with immune responses.
17
Q
What are the two types of immune responses?
A
- Nonspecific immune response: offers resistance to any microbe or foreign material
- AKA nonspecific resistance, innate immunity, and natural immunity
- Natural immune response: resistace to a particular foreign agent
- AKA acquired immunity, adaptive immunity and specific immunity
- Improves on repeated exposure to agent
18
Q
What is a parasitic organism? What is parasitism? What is a parasite?
A
Parasitic organism: a symbiont that harms or lives at the expense of its host
Parasitism: relationship between a parasite and its host
Parasite: by convention, when used without qualification, refers specifically to protozoan or helminthic organism
19
Q
What are the two types of parasites?
A
Ectoparasite: lives on surface of host
Endoparasite: lives within host
20
Q
What are the four different types of hosts?
A
Final host: host on (or in) which parasite either gains sexual maturity or reproduces
Intermediate host: serves as temporary but essential environment for some stage of parasite’s development
Transfer host: is not necessary for development but serves as vehicle for reahing final host
Reservoir host: nonhuman organism infected with a parasite that can also infect human
21
Q
Define infection.
A
Infection: growth and multiplication of parsite on or within host
22
Q
Define pathogen:
A
Pathogen: any parasitic organism that causes infecious disease
Primary (frank) pathogen: causes disease by direct interaction with host
Opportunistic pathogen: causes disease only under certain circumstances
23
Q
What are the factors impacting outcome of host-parasite relationships?
A
- Number of organisms present
- Virulence of pathogen
- Virulence factors: products or structural components that contribute to virulence or pathogenicity
- Host’s defenses or degree of resistance
24
Q
What is virulence?
A
- Degree or intensity of pathogenicity
- Determined by three characteristics of the pathogen
- Invasiveness: ability to spread to adjacent tissues
- Infectivity: ability to establish focal point of infection
- Pathogenic potential: degree to which pathogen can cause damage to host.
25
What are the 7 mechanisms of pathogenesis of bacterial diseases?
* Maintain a reservoir: place to live before and after causing infection
* Be transported to host
* Adhere to, colonize, and/or invade host
* Multiply or complete life cycles on or in host
* Initially evade hose defenses
* Damage host
* Leave host and return to reservoir or enter new host
26
Elaborate on "maintaining a reservoir", a mechanism of pathogenesis of diseases.
* For human pathogens, most common reservoirs are:
* Other humans
* Animals
* Environment
27
Elaborate on "transport of the pathogen to a host", a mechanism of pathogenesis of diseases.
* Direct contact
* e.g. coughing, sneezing, body contact
* Indirect contact
* Vehicles (e.g. soil, water, food)
* Vectors: living organisms that transmit pathogen
* Foimtes: inanimate objects that harbor and transmit pathogens
28
Elaborate on "attachment and colonization", a mechanism of pathogenesis of diseases.
* **Adherence**: mediated by special molecules or structues called adhesins
* **Colonization**: establishment of a site of microbial reproduction on or within host
29
Elaborate on "invasion of the bacterial pathogen", a mechanism of pathogenesis of diseases.
* Can be active penetration of host's mucous membranes or epithelium
* Can be passive penetration
* e.g., skin lesions, insect bites, wounds
* Once below mucous membrane, bacterium can spread to deeper tissues
* Involves productin of specific products and/or enzymes tat promote spreading
30
Elaborate on "growth and multiplication", a mechanism of pathogenesis of diseases.
* Occurs when pathogen finds appropriate environment within host
* Some bacteria invade specific cells
* Some actively grow in blood plasma
* **Bacteremia**: presence of viable bacteria in blood.
* **Septicemia**: presence of bacteria or their toxins in bloodstream.
31
Elaborate on "leaving the host", a mechanism of pathogenesis of diseases.
* Must occur if microbe is to be perpetuated
* Most bacteria leave by passive mechanisms
* E.g., feces, urine, droplets, saliva, or desquamated cells
32
How are bacterial virulence factors regulated?
* Often environmental factors control expression of virulence genes
* e.g., Corynbacterium diptheriae: gene for diphtheria toxin regulated by iron
* e.g. Bordetella pertussis: expression of virulence gees increased at body temperature
* Vibrio cholerae: gene for cholera toxin regulated b pH, temperature, and other factors
33
What are pathogenicity islands?
* Large segments of DNA that carry virulence genes
* Acquired during evolution of pathogen by horizontal gene transfer
* E.g. genes for type III secretion system
* enables gram-negative bacteria to secrete and inject virulence proteins into cytoplas of eukaryotic host
34
Define the following: intoxications, toxin, toxemia, and antitoxins.
**Intoxications**: diseases tht result from entry of a specific preformed toxin into host
**Toxin**: specific substance that damages host
**Toxemia**: condition caused by toxins in the blood of host
**Antitoxins**: neutralizing antibodies
**Toxoid**: inactivated toxin used to elicit immune response.
35
What are exotoxins?
* They typically can be AB exotoxins: composed of two subunits -
* A subunit - responsible for toxic effect
* B subunit - binds to target cell
* They can also be hemolytic reactions:
* **Beta-hemolysis**: complete lysis
* Observed as zone of clearing around colony on blood agar
* **Alpha-hemolysis**: partial lysis
* Observed as geenish zone around colony on blood agar
* Can also employ phospho-lipases: exotoxin removes the charged polar head groups from the phospholipid part of the host cell membrane. This destablizies the membrane and causes the host cell to lyse.
36
What are the 3 roles of exotoxin in disease?
* Ingestion of preformed exotoxin (intoxications)
* Colonization of mucosal surface followed by exotoxin production
* Colonization of wound followe by local exotoxin production
37
What are endotoxins?
* Lipopolysaccharide complex on outer membrane; lipid A portion is toxic
* Usually capable of producing general systematic effects: fever, shock, blood coagulation, weakness, diarrhea, inflammation, intestinal hemorrhage, fibriolysis.
* Bring about these effects indirectly
* Endotoxin interacts with host molecules and cells, activating host systems
* e.g., interaction with macrophages -\> release of endogenous pyrogen
* e.g., binding to LPS-binding protein -\> release of cytokines
38
How do viruses evade the immue system?
* Mutations that change antigenic sites or alter expression of antigens
* Infection of immune system cell, diminishing their function
* Infection of tisues with few MHC molecules
* Production of proteins that inhibit MHC molecule function
* Production of free antigens that bind neutralizing antibodies
39
How do bacteria evade the immune system?
* Have mechanisms to resist complement system, phagocytosis, and specific immune responses
* Evading the complement system:
* Capsules
* Lengthened O-chains
* **Serum resistance**: modified lipooligosaccharides interfere with formation of membrane attack complex.
* Resisting phagocytosis involves:
* Capsules
* Production of specialized surface proteins that block adherence of phagocytes to bacterium
* Production of proteases that cleave complement factor C5a (phagocyte chemoattractant)
40
How do bacteria survive inside phagocytic cells?
* Escape from phagosome before fusion with lysosome
* Resistance to toxic products of phagolysosome
* Prevent fusion of phagosome and lysosome
41
How do bacteria evade specific immune responses?
* Evading specific immune response by:
* Capsules
* Genetic variation of surface antigens
* Production of IgA proteases
* Production of proteins that interfere with antibody-mediated opsonization
**Opsonization**: the process by which a pathogen is marked for ingestion and destruction by a phagocyte
