MFD.10

Question 1

How do bacteria cause disease:

1) Pathogen
2) Opportunistic pathogen
3) Infection

Answer 1

• PATHOGEN: An organism that causes disease in otherwise healthy individuals
• OPPORTUNISTIC PATHOGEN: An organism which requires the host to have a pre-¬‐existing defect in its defences before it can cause disease
• INFECTION: Growth of a non-¬‐native microorganisms at a body site, with or without damage to the host
•

Question 2

How do bacteria cause disease:

1) virulence
2) virulence factors

Answer 2

VIRULENCE: a measure of the capacity of an organism to cause disease
• VIRULENCE FACTORS: properties of a bacterium which contribute to its virulence

Question 3

What are the 2 types of infection?

Answer 3

1) Endogenous

2) Exogenous

Question 4

Define Endogenous infections:

Answer 4

are caused by an infectious agent that is already present in the body, but has previously been inapparent or dormant

Question 5

Define endogenous infections:

Answer 5

are caused by an infectious agent that is already present in the body, but has previously been inapparent or dormant

Question 6

Define Exogenous infections:

Answer 6

are acquired from sources outside the patient

Question 7

Pathogens possess a range of virulence factors. Name them:

Answer 7

– Adhesins
– Invasins (enter cells )
– Toxins
– Extracellular enzymes

Question 8

What are the stages of infection?

Answer 8

1) Exposure
2) Adherence
3) Invasion
4) Infection
5) THEN..
Toxicity: toxin effects are local or systemic
OR
Invasiveness: Further growth at original and distant sites
6) Tissue Damage, disease

Question 9

Adherence
Initial attachment involves interaction between surface structures of bacteria and host tissue. What structures are used to do this?

Answer 9

1. Bacterial surface structures -¬‐ pili, fimbriae, surface proteins
2. Host tissue receptors —glycoproteins, tissue— specific antigens (HLA etc.)

Question 10

What are the innate ways the host defends itself from pathogens?

Answer 10

• Skin (keratinised, shedding of outer layers)
• Flushing (saliva, urine, peristalsis in gut)
• Secretions (lysozyme, stomach acid, bile salts)
• Mucous membranes (cilia)
• Normal bacterial population (colonisation resistance)

Question 11

What are the adaptive ways the host defends itself from pathogens?

Answer 11

• Phagocytosis
• Inflammation, fever
• Antibodies

Question 12

Explain how bacteria evade the following adaptive immune responses:

1) Phagocytosis
2) Inflammation/fever
3) Antibody

Answer 12

Phagocytosis: Capsules (prevent antibody attachment enabling phagocytosis)
Inflammation/fever: Heat shock response (lets them survive the higher temperature)
Antibody: Breakdown of immunoglobulins, kill host defence cells, intracellular

Question 13

What are commensal flora?

Answer 13

friendly bacteria, provide us with benefits

Question 14

How do bacteria evade normal bacterial population/ commensal bacteria?

Answer 14

Metabolic end products, bacteriocins, bacteriophage etc

Question 15

What is bacteraemia

Answer 15

• Invasion into bloodstream

Question 16

What is septicaemia.

Answer 16

• Infection in the bloodstream

Question 17

What is the name given to the following definition:

• Invasion into bloodstream

Answer 17

bacteraemia

Question 18

What is the name given to the following definition:

• Infection in the bloodstream

Answer 18

septicaemia.

Question 19

Following attachment after invasion, what do the bacteria then do?

Answer 19

invade epithelial cells

Question 20

Compare the terms infection and disease:

Answer 20

• Infection is a situation when a microorganism that is not a natural (commensal) coloniser grows within the host, whether or not it causes damage.
• Disease arises when there is damage to the host.

Question 21

How can the bacteria spread once within the cells of a host?

Answer 21

• Through lungs, gut, urinary tract, blood
• via sinuses and body cavities
• Tracking along nerve pathways
• Direct cell-¬‐to-¬‐cell
• Tissue breakdown

Question 22

Give the 2 types of toxins ( a microbial virulence factor):

Answer 22

1) endotoxin

2) exotoxin

Question 23

Give the 3 types of tissue-degrading enzymes( a microbial virulence factor):

Answer 23

• collagenase
• hyaluronidase
• haemolysin

Question 24

Give an example of an endotoxin found only in gram-negative bacteria:

Answer 24

LPS

Question 25

What is LPS

Answer 25

an endotoxin found only in gram-negative bacteria:

Question 26

Where is LPS present in gram-negative bacteria?

2) When is it released?
3) What does it cause in the host?

Answer 26

1) outer layer of the outer membrane
2) released during growth or when bacteria die and lyse
3) fever, septic shock and local inflammation

Question 27

How are they released?

2) What type of bacteria produce them (gram)?
3) Describe its stability and toxicitiy?

Answer 27

1) Secreted by bacteria
2) + and -
3) relatively unstable and highly toxic

Question 28

Damadge by exotoxin does not require a bacterial infection, so how would it be treated?
2) What would we normally do and why doesn’t it work?

Answer 28

1) vaccines given that target the toxin

2) give antibiotics that target the infectious agent i.e. the bacterium therefore useless

Question 29

What bacteria causes very swollen pseudomembranes in the posterior pharynx? ( so swollen can obstruct airways)

2) What is the vaccine based on?
3) What carries the toxin? what does the toxin do?

Answer 29

Diphtheria

2) inactivated toxin
3) bacteriophage, inhibits protein synthesis

Question 30

Why do we cook tin foods to 121 degrees?

2) Descibe bacteria’s toxin’s potency?

Answer 30

to protect against botulism (Clostridium botulinum )

2) very high

Question 31

What is a symptom of tetanus?

2) How does Clostridium tetani cause this?

Answer 31

1) muscule contraction (e.g. lockjaw)
2) Secretes a powerful neurotoxin that blocks the release of neurotransmitters from the presynaptic membranes of inhibitory nerve synapses

Question 32

What is the name given to the disease that produces a toxin that causes tissue destruction?

2) How does it do this?
3) Is it an organism or organisms that cause it? +e.g. *2
4) treatment?

Answer 32

1) Necrotising Fasciitis
2) toxin initiates an overactive immune response
3) Can be single organism or polymicrobial
– Most common monoinfections are Streptococcus pyogenes and MRSA
4)surgical debridement

Question 33

chronic vs acute infection

Answer 33

• Acute infection: short duration (days).

* Chronic infection: long duration (weeks to months).

Question 34

What factors influence susceptibility to disease?

Answer 34

• Trauma
• Underlying disease or other infections
• Age
• Genetic constitution (tissue type etc)
• Nutrition
• Hormonal factors and stress
• Pollutants

Question 35

Give examples of trauma that would increase susceptibility to disease: (2)

Answer 35

– accidental (wounds, burns)

– intentional (surgery)

Question 36

Give examples of underlying disease or other infections that would increase susceptibility to disease: (2)

Answer 36

– e.g. viral infections increase risk of bacterial pneumonia;
- HIV immunosuppression increases other infections