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MCB3020 Exam 3 > Lecture 20 General Microbiology > Flashcards

Lecture 20 General Microbiology Flashcards

1
Q

What is pathogenicity?

A
  • Ability to produce pathological change or disease
  • Pathogen: any disease-producing microorganism.
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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.
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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
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4
Q

How do you establish gnotobiotic animal colonies in BIRDS?

A
  • Germicide treatment of fertile eggs
  • Hatch eggs in sterile isolators
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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
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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

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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
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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)
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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.
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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
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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.
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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
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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.
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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
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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.
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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.
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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
Q

What are the 7 mechanisms of pathogenesis of bacterial diseases?

A
  • 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
Q

Elaborate on “maintaining a reservoir”, a mechanism of pathogenesis of diseases.

A
  • For human pathogens, most common reservoirs are:
    • Other humans
    • Animals
    • Environment
27
Q

Elaborate on “transport of the pathogen to a host”, a mechanism of pathogenesis of diseases.

A
  • 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
Q

Elaborate on “attachment and colonization”, a mechanism of pathogenesis of diseases.

A
  • Adherence: mediated by special molecules or structues called adhesins
  • Colonization: establishment of a site of microbial reproduction on or within host
29
Q

Elaborate on “invasion of the bacterial pathogen”, a mechanism of pathogenesis of diseases.

A
  • 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
Q

Elaborate on “growth and multiplication”, a mechanism of pathogenesis of diseases.

A
  • 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
Q

Elaborate on “leaving the host”, a mechanism of pathogenesis of diseases.

A
  • Must occur if microbe is to be perpetuated
  • Most bacteria leave by passive mechanisms
    • E.g., feces, urine, droplets, saliva, or desquamated cells
32
Q

How are bacterial virulence factors regulated?

A
  • 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
Q

What are pathogenicity islands?

A
  • 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
Q

Define the following: intoxications, toxin, toxemia, and antitoxins.

A

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
Q

What are exotoxins?

A
  • 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
Q

What are the 3 roles of exotoxin in disease?

A
  • Ingestion of preformed exotoxin (intoxications)
  • Colonization of mucosal surface followed by exotoxin production
  • Colonization of wound followe by local exotoxin production
37
Q

What are endotoxins?

A
  • 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
Q

How do viruses evade the immue system?

A
  • 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
Q

How do bacteria evade the immune system?

A
  • 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
Q

How do bacteria survive inside phagocytic cells?

A
  • Escape from phagosome before fusion with lysosome
  • Resistance to toxic products of phagolysosome
  • Prevent fusion of phagosome and lysosome
41
Q

How do bacteria evade specific immune responses?

A
  • 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

MCB3020 Exam 3 (8 decks)

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