Cell Structures - Virulence Factors And Toxins

Question 0

What kinds of flagella can bacteria have?

Answer 0

1. Single polar flagellum : Vibrio cholera.
2. Many peritrichous flagella all around the cell : E.coli and Proteus mirabilis.
3. Periplasmic flagella : spirochetes.

Question 1

What is the structure by which the flagellum is affixed to the bacteria?

Answer 1

By a basal body, which spans through the entire cell wall, binding to the inner and outer cell membrane in gram negative bacteria and to the inner membrane in gram-positive bugs (the gram-positive bacteria don’t have an outer membrane).

Question 2

Does shigella have flagella?

Answer 2

No!

Question 3

What are the Pili (also called fimbriae)?

Answer 3

1. Straight filaments arising from the bacterial cell wall, making the bacterium look like a porcupine.
2. They are much shorter than flagella and do not move.
3. Serve as adherence factors - adhesins.

Question 4

Mention some bacteria that have pili and utilize them as adhesins.

Answer 4

1. Neisseria gonorrhea : pili that allow it to bind to cervical cells and buccal cells to cause gonorrhea.
2. E. coli + Campylobacter jejuni cannot cause diarrhea without their adhesins to bind to the intestinal epithelium.
3. Bordetella pertussis uses its adhesin to bind to ciliated respiratory cells and cause whooping cough.

Question 5

What are the components of the bacterial capsule?

Answer 5

They are usually composed of simple sugar residues.

Bacteria secrete these sugar moieties, which then coat their outer wall.

Question 6

What is unique about Bacillus anthracis’ capsule?

Answer 6

It is made up of amino acid residues.

Question 7

What is the main significance of a bacterial capsule?

Answer 7

Capsules enable bacteria to be more virulent because macrophages and neutrophils are unable to phagocytize the encapsulated buggers. (e.g. Streptococcus pneumoniae)

Question 8

What are the two important tests that enable doctors to visualize capsules under the microscope and aid in identifying bacteria?

Answer 8

1. India ink stain : the capsule appears as a transparent halo around the cell. (used primarily to identify the fungus Cryptococcus)
2. Quelling reaction : bacteria are mixed with antibodies that bind to the capsule.

Question 9

What contains a vaccine against streptococcus pneumoniae?

Answer 9

Antigens from the 23 most common types of capsules.

Question 10

What are the two genera of bacteria that form endospores?

Answer 10

1. The aerobic Bacillus
2. The anaerobic Clostridium
   Both gram positive.

Question 11

What are the components of the endospores multilayer?

Answer 11

1. A cell membrane
2. A thick peptidoglycan mesh
3. Another cell membrane
4. A wall of keratin-like protein
5. An outer layer called the exosporium

Question 12

What is a biofilm?

Answer 12

An extracellular polysaccharide network, similar to the capsule polysaccharides, that forms a mechanical scaffold around bacteria. It allows them to bind to prosthetic devices, like IV catheters, and protects them from attack by antibiotics and the immune system.

Question 13

What is the main action of facultative intracellular organisms?

Answer 13

These bacteria inhibit phagosome-lysosome fusion.

Question 14

Mention 8 important facultative intracellular organisms.

Answer 14

1. Listeria monocytogenes
2. Salmonella typhi
3. Yersinia
4. Francisella tularensis
5. Brucella
6. Legionella
7. Mycobacterium
8. Nocardia

Question 15

Describe briefly what the exotoxins are.

Answer 15

Proteins released by both gram positive and gram negative bacteria.

Question 16

What diseases can exotoxins cause?

Answer 16

1. Anthrax
2. Botulism
3. Tetanus
4. Cholera

Question 17

What are the neurotoxins?

Answer 17

Exotoxins that act on the nerve or motor endplates to cause paralysis. Tetanus toxin and botulinum toxin are examples.

Question 18

What are the enterotoxins?

Answer 18

Exotoxins that act on the GI tract to cause diarrhea.

Question 19

What are the main actions of enterotoxins?

Answer 19

1. Inhibit NaCl resorption
2. Activate NaCl secretion
3. Kill intestinal epithelial cells
   Common end result : the osmotic pull of fluid into the intestine, which causes diarrhea.

Question 20

What are the two diseases caused by enterotoxins?

Answer 20

1. Infectious diarrhea

2. Food poisoning

Question 21

Mention some bacteria that can cause infectious diarrhea.

Answer 21

1. Vibrio cholera
2. Escherichia coli
3. Campylobacter jejuni
4. Shigella dysenteriae

Question 22

Mention some bacteria that cause food poisoning.

Answer 22

1. Bacillus cereus

2. Staphylococcus aureus

Question 23

What are the pyrogenic exotoxins?

Answer 23

Stimulate the release of cytokines and can cause rash, fever, and toxic shock syndrome.

Question 24

Mention 2 bacteria that can release pyrogenic exotoxins.

Answer 24

1. Staphylococcus aureus

2. Streptococcus pyogenes

Question 25

What are the tissue invasive exotoxins?

Answer 25

Exotoxins that allow bacteria to destroy and tunnel through tissues.
These include enzymes that destroy DNA, collagen, fibrin, NAD, RBCs, and WBCs.

Question 26

What are the exotoxin subunits in Bacillus anthracis, Clostridium botulinum, Clostridium tetani, Corynebacterium diphtheriae, and Vibrio cholera?

Answer 26

Composed of 2 polypeptide subunits bound together by disulfide bridges.

Question 27

How are the two subunits of exotoxin called?

Answer 27

One is called B for binding of H for holding : binds to the target cell.
The other subunit called A for action or L for laser : enters the cell and exerts the toxic effect.

Question 28

Why sometimes treating a patient who has a gram negative infection with antibiotics can worsen the things?

Answer 28

Because all the bacteria are lysed, releasing large quantities of endotoxin.

Question 29

How is endotoxin different from exotoxin?

Answer 29

Endotoxin differs from exotoxin in that it is not a protein excreted from cells, but rather is a normal part of the outer membrane that sort of sheds off, especially during lysis.

Question 30

What bacteria can cause septic shock?

Answer 30

Both gram positive and gram negative.

Question 31

What is the different between bacteremia and sepsis?

Answer 31

Bacteremia : bacteria in the blood-stream.

Sepsis : bacteremia that causes a systemic response to the infection.

Question 32

Mention 4 bacteria that produce exotoxins that increase levels of cAMP.

Answer 32

1. Vibrio cholera
2. Bacillus anthracis
3. E.coli (Montezuma’s revenge)
4. Bordetella pertussis