Topic 1-8 (Lecture 8)

Question 1

What is pathogenicity?

Answer 1

The qualitative ability of a bacterium to cause disease

e.g. it can, it can’t

Question 2

What is a pathogen?

Answer 2

A bacterium that is capable of harming a normal host (normal meaning no compromise in immune system)

Capable does NOT mean ALWAYS will cause harm, it just CAN cause harm

Question 3

What is an opportunistic pathogen?

Answer 3

A bacterium that harms a compromised host

Question 4

What is virulence?

Answer 4

The QUANTITATIVE measure of the pathogenicity of a microorganism (expressed it number ocells that will cause disease (ID50) and will kill (LD50))

Question 5

What are commensals?

Answer 5

Bacteria of the microbiota

Question 6

What is do commensals and opportunistic pathogens lack?

Answer 6

They lack an inherent ability to cause disease (lack a genetic component to cause disease/harm host)

Question 7

What does pathogenicity indicate?

Answer 7

The ability of an organism to cause disease

Question 8

What does virulence indicate?

Answer 8

The extent of a disease cause by an organism

Question 9

What are some factors affecting virulence?

Answer 9

Route of entry
Susceptibility/general health of host
Ability to multiply within the host

Question 10

What are the two extremes of virulence?

Answer 10

Highly virulent - causing disease in most individuals

Avirulent - rarely causing disease (if ever)

Question 11

What are virulence factors?

Answer 11

Factors that allow a microorganism to enter and colonize in a host, resist the immune defences of a host, and cause damage in the host

Question 12

What are the different classification of bacterial infections?

Answer 12

Primary
Secondary
Subclinical
nosocomial
local infection
systemic/generalized
focal

Question 13

What is a primary infection?

Answer 13

The initial, acute infection of bacteria

Question 14

What is a secondary infection?

Answer 14

The later, “second” infection caused by an opportunistic organisms after the primary infection has weakened the host defences

Question 15

What is a subclinical infection?

Answer 15

An infection in which the host has no apparent symptoms

Question 16

What is a nosocomial infection?

Answer 16

An infection which is acquired as a consequence of hospitalization

Question 17

What is a local infection?

Answer 17

An infection restricted to a small area of the body (usually caused by non-invasive organisms)

Question 18

What is a systemic/generalized infection?

Answer 18

An infection which spreads throughout the body (usually caused by invasive organisms, often via the blood)

Question 19

What is a focal infection?

Answer 19

An infection that begins in a restricted area then spreads throughout the body

Question 20

What is invasiveness?

Answer 20

The ability of an organism to invade/spread beyond the original site of entry into a host’s body

Question 21

What influences the interaction between microorganisms and the host?

Answer 21

The virulence of the microorganisms

The anti-bacterial defenses of the host

Question 22

What factors can compromise the immune defence?

Answer 22

Underlying disease/infection

Stress

Poor nutrition (body can’t fight if it doesn’t have the energy)

Immunosuppressive therapy (ex. during maintenance of transplanted organs)

Age (underdeveloped immune defences in newborn and infants make them weak; degeneration of immune defences when old also make them weak)

Genetics (some individuals are more resistant or more susceptible; think of HLA’s for MHC proteins)

Question 23

What do bacteria rely on to cause disease?

Answer 23

Virulence factors

Question 24

What is pathogenesis dependent on?

Answer 24

Having multifactotrial bacteria; bacteria with multiple virulence factors

Question 25

What is bacteremia?

Answer 25

The presence of bacteria in the blood

Question 26

What is septicaemia?

Answer 26

The multiplication of bacteria in the blood

Question 27

What are facultative intracellular pathogens?

Answer 27

Pathogens that can live within or outside host cells

facultative - capable of but not restricted to a particular function or mode of life

Question 28

What are obligate intracellular pathogens?

Answer 28

Pathogens that MUST live within host cells (cannot be cultivated ouside host)

(obligate - by necessity)

Question 29

Why is the intracellular environment desirable for bacteria?

Answer 29

Has a rich source of nutrients and energy (ex. AA’s, ATP, NTP)

Has protection against immune system (eg. Ab, complement, neutrophils)

Provides protection from many antibiotics

Question 30

How do extracellular bacterial pathogens cause disease?

Answer 30

Usually due to release/injection of proteinaceous (containing protein) exotoxins and/or effectors which cause cell death and inflammatory responses (eventually)

Question 31

What are some examples of extracellular pathogen defense mechanisms?

Answer 31

Capsules, adhesins, enzymes that resist oxidative stress

Question 32

How do bacteria adhere to host tissue?

Answer 32

Attachment is done using an adhesin on bacteria attaching to a receptor on the host cell surface (ex. glycoprotein)

Often host specific and tissue specific (only works for some species and for particular tissue type)

Question 33

What are the advantage of adhering to host cells?

Answer 33

Facilitates colonization
Prevents removal by non-specific host defence systems (ex. mucus)
Localizes bacterium on appropriate tissue

Question 34

How does the host respond to adherent bacteria?

Answer 34

1) Producing Ab against bacteria
2) Upregulating antimicrobial peptides by epithelial cells
3) Phagocytosis of adherent organisms
4) Shedding/destruction of colonized epithelial cells

Question 35

What mechanisms are used by bacteria to avoid phagocytosis and immune responses? (ex. binding of complement or Ab)

Answer 35

Membrane bound proteins
Slimy polysaccharide capsules
LPS

Question 36

What are toxins?

Answer 36

Microbial products that can damage the host independent of the bacterium (meaning the toxin can cause damage even w/o the bacterium present)

Question 37

What are the 2 types of toxins?

Answer 37

Exotoxins and Endotoxins

Question 38

What are exotoxins?

Answer 38

Secreted proteins from both Gram-positive and Gram-negative bacteria

Question 39

What are the 3 categories of exotoxins and their effects/targets?

Answer 39

Cytolytic toxins - cause cell lysis (attacks cells)

Neurotoxins - interfere with nerve cell function

Enterotoxin - cause massive fluid secretion in gastrointestinal tract epithelium (i.e. diarrhea)

Question 40

What are properties of exotoxins?

Answer 40

Extremely potent - small dose has significant effects

Are proteins -> thus are heat labile (i.e. easily broken down with heat)

Immunogenic -> i.e. causes an immune response and stimulates Ab production

Question 41

What are toxoids?

Answer 41

Toxins that have been treated with heat or chemicals to make them non-toxic to people, but still retain their immunogenic attributes

Question 42

What are toxoids used for?

Answer 42

To vaccinate people against toxin-mediated diseases

Question 43

What are endotoxins?

Answer 43

Non-protein molecules that are released when bacteria die or are phagocytized

Question 44

What do endotoxins do?

Answer 44

Bind to TLR-4 and stimulate inflammatory response

Question 45

What is the danger of endotoxins?

Answer 45

Low doses cause fever (it is pyrogenic), malaise (general discomfort), aches and pains

In higher doses, causes endotoxin shock (which is potentially fatal)

Question 46

What is endotoxin shock?

Answer 46

Basically anphlactic shock;

• leakage of fluid out of blood vessels
• Blood coagulation
• Drop in blood pressure
• organ failure

Question 47

How are endotoxins treated?

Answer 47

Using supportive therapy (antibotics cannot be used, since it would aggravate endotoxin release)