Bacteria

Question 1

What is flora?

Answer 1

Commensal bacteria that has a role in immune system development. Alterations in the flora leaad to dysfunction.

Question 2

What is the consequence of alteration in gut flora?

Answer 2

Leads to growth of Clostridium difficile that causes antibiotic associated colitis.

Question 3

Why are faecal transplants done?

Answer 3

The bacteria within is used to treat and improve gut health.

Question 4

What is a nucleoid?

Answer 4

An irregular shaped region which contains most of the free floating genetic material.

Question 5

What is the process of gram staining?

Answer 5

Stained with violet stain and iodine, washed with alcohol and counterstained with pink safarin.

Question 6

What are the results of gram staining?

Answer 6

Gram +ve = Purple due to thick peptidoglycan layer

Gram -ve = Pink due to the thin peptidoglycan layer

Question 7

What are gram -ve bacteria?

Answer 7

These bacteria have a highly modified outer membrane of sugars, an inner membrane, a thin layer of peptidoglycan and the three layers are separated by periplasm. Contains LPS.

Question 8

What is LPS?

Answer 8

A potent activator of the immune system causing endotoxic shock.

Question 9

What test is used to identify the strain?

Answer 9

Matrix-associated laser desorption ionization time of flight mass spectrometry

Question 10

How can bacteria cause infection?

Answer 10

• Attachment to host via pilli to receptors induces uptake for intracellular survival and avoidance of phagocytosis.
• Invasion of tissue using type 3 secretion
• Acquire nutrients for growth by producing high affinity siderophores to take from the host.
• Avoidance of immune system
• Cause damage directly through toxins or indirectly by overactivating the immune response

Question 11

What is the mechanism of type 3 secretion?

Answer 11

Effector molecules are injected into the host to alter their cytoplasm and manipulate protein functions for bacterial uptake.

Question 12

How does a host alter its iron availability during an infection?

Answer 12

Host tries to withhold iron by binding to transferrin and reducing free levels.

Question 13

How might bacteria avoid the immune system?

Answer 13

Inhibit phagocytosis, antigen presentation, apoptosis, block cell cycle, Ig binding proteins, inappropriate T cell activation

Question 14

How does LPS overactivate the immune system?

Answer 14

Overactivates cytokine production causing sepsis or molecular mimicry

Question 15

What is molecular mimicry?

Answer 15

Components similar to the host causing cross reactions with host antigens

Question 16

What is sepsis?

Answer 16

Over activation of the immune system leading to organ failure due to widespread vasodilation, dramatic fall in BP and reduced organ perfusion.

Question 17

What is the process that occurs with a normal infection?

Answer 17

Detection of bacterial products activates macrophages to secrete substances that increase vascular permeability. Local vessels occlude to prevent reentry of immune cells into the circulation, to drain to lymph.

Question 18

What happens if the infection is systemic?

Answer 18

Fluid accumulates in the tissues due to widespread permeability. Blood volume fall and BP drops causing vessels to collapse and intravascular coagulation leads to necrosis and organ failure.

Question 19

How does sepsis present?

Answer 19

Fever, confusion, hypotension, reduced urine output

Question 20

Give an example of molecular mimicry.

Answer 20

The presence of stretococci group A and acute rheumatic fever causes the immune system to produce crossreactive antistreptococcal Ig that are autoIg to myosin which react with heart, lung and kidney.
or
Stretococci group A and glomerulonephritis causes production of Ig that are crossreactive with laminin, collagen and basement membrane.

Question 21

What is the link between Helicobacter pylori and cancer?

Answer 21

Cog A is injected into the host via type 4 secretion and it phosphorylates to form a complex with tyrosing phosphate to induce GF like response, resulting in uncontrolled cell division.

Question 22

What is the link Typhi and cancer?

Answer 22

Typhi causes chronic infection of the gall bladder. It causes degradation of bile for the source of nutrients but this produces carcinogenic compounds.