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Introduction to Medical Microbiology > Lecture 4- Pathogenesis > Flashcards

Lecture 4- Pathogenesis Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Modes of Transmission of disease?

A
  • Direct contact
  • Indirect contact
  • Vectors
  • Fomites (inanimate objects)
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2
Q

Examples of direct contact?

A 

cough

sneeze

touch
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3
Q

Examples of indirect contact?

A 

food

water

soil
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4
Q

First step in establishment of disease?

A

entrance and attachment

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5
Q

Example of portal of entry for disease?

A


skin, respiratory, gastrointestinal, urogenital systems, or conjunctiva of eye

vector borne, sexual contact, blood transfusion, or organ transplant

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6
Q

What is adherence of disease mediated by

A

special molecules called adhesins

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7
Q

Define colonisation?

A

site of microbial reproduction on or within host

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8
Q

In establishment of disease what to organisms compete for?

A

•
Compete for nutrients
•
Compete for colonisationsites

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9
Q

Define adhesions?

A

adherence factors/molecules

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10
Q

Define Fimbriae?

A

includes pili/organelles that project from the cell surface to mediate attachment to host cell surface receptors

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11
Q

What is a Glcocalyx and function?

A 
Capsule/slime layer made up of glycoproteins and or polysaccharides.

sticky (adherent, resist cough reflex)

resists phagocytosis
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12
Q

How do adherence structure general work?

A

bind complementary receptor sites on host cell surface

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13
Q

Example of organism that usres fimbriae to colonise?

A 
Neisseria gonorrhoeae (GNC –diplococcus)uses fimbriae to initially colonise
the urethral or cervical epithelium.
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14
Q

Types of entry in establishment of disease?

A
  • No entry Required
  • Passive entry
  • Active Entry
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15
Q

Example of disease that does not require entry?

A

N.gonorrhoeae– sexual activity (intercourse,oral,anal)

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16
Q

Define passive entry and give example?

A

Organism that without a defined entry mechanism would not cause disease
eg Insect bites, surgery

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17
Q

Example of active entry?

A

Invasins stimulate host cells to ingest bacteria

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18
Q

What is an invasin

A

Surface proteins that provoke ingestion of bacteria by host cells

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19
Q

Define Bacteremia?

A

presence of viable bacteria in the blood

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20
Q

Define spepticemia?

A

pathogens or their toxins in the blood

21
Q

Conditions needed for growth and multiplicaiton of disease?

A

Suitable nutrients, pH, Temperature and redox potential (affects the amount of O2 present)

22
Q

Virulence factors of Extracellular enzymes

A
  • Collagenase
  • Hyaluronidase
  • Lecithinase
  • Coagulase
  • Fibrinolysin
  • IgA Protease
  • NucleaseCatalase, peroxidase, superoxide dismutase
23
Q

Collagenase and hyaluronidase?

A

Proteolytic enzymes that breakdown collagen and hyaluronic acid in connective tissue allowing an organism to spread into neighbouring tissues

24
Q

Lecithinase?

A

breaks down the phospholipid layer of cell membranes and causes extensive cell & tissue damage

25
Q

Coagulase

A

produced by S.aureus, causes fibrinogen to form a fibrin clot around bacteria and prevent phagocytosis

26
Q

Fibrinolysin

A

has the opposite effect to coagulase by dissolving a fibrin clot and is thought to assist the pathogen by preventing localisation of the infection by the inflammatory response

27
Q

Nuclease

A

breaks down viscous nucleic acids released by the lysis of WBC during pus formation allowing bacteria to continue to spread

28
Q

Catalase, peroxidase, superoxide dismutase

A

these enzymes inhibit the reactive oxygen species produced during the oxidative response following phagocytosis by neutrophils, monocytes and macrophages

29
Q

Virulance Factors of school sores “Impetigo”

A

Rapid spread of infection caused by enzymes collagenase, hyaluronidase, fibrinolysin and nuclease.

30
Q

Protein A?

A

 binds to Fc portion of IgG molecules

 Antibodies are not recognised by phagocytes

31
Q

What is Hemolysins?

A

Virulance factor

32
Q

Pigments (carotenoids)

A

 Toxic to other organisms and to some human tissues

 Inhibit immune function

33
Q

What is an Exotoxin and eg?

A

• Proteins that are secreted/released by bacteria (generally Gram positive)
eg Examples:
•Clostridium tetani (tetanus) -Vibrio cholerae (cholera enterotoxins)

34
Q

Properties of Exotoxins?

A
  • Heat libale
  • Extremely potent
  • Antigenic
  • Converted to toxoids for vaccine
35
Q

Diphtheria Toxin?

A

• A cytotoxic exotoxin that can cause organ damage (i.e. heart, liver, throat)

36
Q

How is diphtheria toxin produced?

A

Produced by toxigenic strains of Corynebacterium diphtheriae that are infected with a lysogenic β phage (not lytic) which is tox pos

37
Q

Remember to look at diagram for diphtheria toxin?

A

Yepp yepp dont forget

38
Q

Define Translation - Protein Synthesis?

A

The elongation cycle is the process of reading mRNA, the insertion of tRNA into the ribosome to produce peptides

39
Q

Properties of Endotoxins

A

-Lipid Aof Gram negative cell wall
-Not secreted-released when cells disrupted
-Heat stable
- Not antigenic
-Activates coagulation, complement, fibrinolysis
- Less potent than exotoxins
 Toxic (nanogram amounts)
- Weakly immunogenic
-Cause general system effects
 fever, weakness, diarrhea, inflammation

40
Q

Which virulence factors may aid the attachment of a pathogen to the body surface?

A

Adhesins, Fimbriae and Glycocalyx

41
Q

What is an endogenous infection?

A

It is an infection by a member of normal flora

42
Q

Why is tetanus described as a focal infection?

A

It is a localised infection from which pathogens can spread to other body sites

43
Q

Explain the emergence of Haemophilus influenzae as a secondary pathogen.

A

This usual follow a primary pathogens as a secondary complication

44
Q

Tuberculosis may progress very slowly over a number of years. What type of infection is this?

A

This is a chronic infection as it slowly progress’s.

45
Q

What is ID50 and what does it measure?

A

It is the number of bacteria nessacary to infect 50% population of people exposed to it.

46
Q

What is a glycocalyx and how can this contribute to the virulence of a pathogen?

A

It is a capsule slim layer made up of glycoproteins or polysaccrides. It contributes to virulence by being sticky (adherent) and resisting phagocytosis.

47
Q

How may collagenase act as a virulence factor?

A

Enzyme that breaks down collagen allowing it to spread into neighbouring tissues

48
Q

What is the basis of the vaccine for tetanus?

A

They uses the Clostridium tetani which is an exotoxin coverted into a toxoid by being formalin treated or heat treated. It remains immunogenic however much less toxic

49
Q

Why does a single molecule of diphtheria toxin subunit A lead to the death of a host cell?

A

It inhibits the production of protein synthesis resulting in cell deaths as it is unable to replicate

Introduction to Medical Microbiology (7 decks)

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