Lecture 2: Cell Structures, Virulence Factors, and Toxins

Question 1

Flagella

-Components

Answer 1

-thin, hollow, helical rods used for motility governed by chemotactic responses
-sps of bacteria can be identified by use of specific antibodies against flagerllar proteins
Components
(1) Basal Body- spans through the entire cell wall and consists of small central rod inserted into series of rings, spins around and spins the flagellum
(2) Hook
(3) Filament -protein filaments that extend like long tails from cell membranes

Question 2

4 Types of Flagella

Answer 2

Monotrichous- single flagellum
   (eg Pseudomonas)
Amphitrichous- two flagella
   (eg Spirillum)
Lophotrichous -two or more flagella at one or both ends
   (eg Spirillum)
Peritrichous -flagella all over surface 
   (eg Salmonella, Proteus)

Question 3

Pili (Fimbriae)

• def
• can serve as ______
• examples
• 2 types

Answer 3

-filamentous protein, much shorter than flagella and do not move
-can serve as adherence factors (aka adhesions)
(eg N. gonorrhea has pili to bind to cervical cells an buccal cells to cause gonorrhea, E. coli and Campylobacter jejuni causes diarrhea using its adhesions to bind the intestinal epithelium)
2 Types:
(1) attachment pili -adheres to surface
(2) conjugation pili (sex pili)

Question 4

Capsules

• composed of
• loosely or firmly attached?
• how does the capsule enable bacteria to become more virulent?

Answer 4

-polysaccharides, form most loosely-associated layer firmly attached to cell wall
-enables bacteria to be more virulent as macrophages and neutrophils are unable to phagocytize the bacteria
(eg smooth and rough colonies of Streptococcus pneumoniae)

Question 5

Tests for visualizing capsules microscopically

Answer 5

India ink stain

Quellung reaction

Question 6

What enables macrophages or neutrophils to phagocytize bacteria?

Answer 6

Opsonization
-antibodies bind to bacterial capsule and enable neutrophils or macrophages to bind to the FC portion of the antibody and phagocytize the bacteria

Question 7

Endospores

Answer 7

• formed due to depletion of essential nutrients and can lie dormant for years
• when spore is exposed to favorable nutrient or environment, it becomes active again
• 2 G(+) Bacillus(aerobic), and Clostridium (anaerobic) form endospores

Question 8

Biofilms

Answer 8

-an extracellular polysaccharide network that forms a mechanical scaffold around bacteria
-binds to prosthetic devices like intravenous catheters
(eg Staphylococcus epidermidis)

Question 9

Facultative Intracellular Organisms

Answer 9

Many bacteria are phagocytosed by the hosts’ macrophages and neutrophils yet survive being unharmed
-can inhibit phagosome-lysosome fusion, escape host’s deadly H2O2 and superoxide radicals
(eg Listeria monocytogenes, Salmonella typhi)

Question 10

Exotoxins

-Gram (+) vs Gram (-)

Answer 10

proteins that are released by both gram (+) and gram (-) bacteria

• released by ALL gram (+)
• some gram (-) like Vibrio cholerae, and E. coli

Question 11

Types of Exotoxins

-Neurotoxins

Answer 11

toxins that act on nerves or motor endplates to cause paralysis
(eg Clostridium tetani and Clostridium botulinum)

Question 12

Types of Exotoxins

-Enterotoxins

Answer 12

exotoxins that act on the GI tract to cause diarrhea
-inhibit NaCl resorption, activate NaCl secretion or kill intestinal epithelial cells resulting in osmotic pull into the intestine which causes diarrhea

Question 13

Disease manifestations of enterotoxins (2x)

Answer 13

(1) Infectious diarrhea -bacteria colonize and bind to the GI tract, releasing their toxins
(eg V. cholerae)
(2) Food Poisoning -bacteria grow in food and release enterotoxin in food, enterotoxin is ingested resulting in diarrhea and vomiting for less than 24hrs
(eg Bacillus cereus and Staphylococcus aureus)

Question 14

Types of Exotoxins

-Pyrogenic

Answer 14

stimulates the release of cytokines and can cause rash, fever, and toxic shock syndrome
(eg Staphylococcus aureus, Streptococcus pyogenes)

Question 15

Types of Exotoxins

 - Tissue invasive
 - Miscellaneous

Answer 15

tissue invasive- allow bacteria to destroy and tunnel through tissues
miscellaneous- can cause disease unique to the individual bacterium

Question 16

Endotoxins

• Gram (+) or Gram (-)
• Lipid ___?
• Released how?
• Differs from exotoxins how?

Answer 16

• Gram (-) ONLY
• Lipid A/Endotoxin is very toxic and is released when bacteria undergoes lysis or released from living bacteria in steady amounts
• Differs from exotoxin as it is not a protein excreted from cells but rather is a normal part of the outer membraned that sort of sheds off, especially during lysis

Question 17

Septic Shock

• Gram (+) or Gram (-)?
• Localized site of infection could result in?
• toxins stimulate which immune cells?
• TNF

Answer 17

• deadly response to both gram (+) and gram (-) bacteria
• localized site of infection could result in bacteremia
• organisms release toxins (endo/exo) that circulate in the bloodstream and stimulate immune cells such as macrophages and neutrophils
• endogenous mediators of sepsis -TNF
  
  • > TNF triggers the release of IL-1 from macrophages and endothelial cells triggering the release of other cytokines and prostaglandins
  • > initially they defend the body against the microbes, ultimately it attacks different organs

Question 18

Septic Shock: Treatment

Answer 18

1) Locate site of infection, identify microbe and eradicate
2) Broad spectrum antibiotics
3) Blood pressure must be supported with fluids and drugs and oxygenation maintained

• Efforts to block inflammatory cascade with monoclonal antibodies against endotoxin, TNF and IL-1, and anti-inflammatory agents have not been very successful
• Recombinant activated protein C (drotrecogin alpha) -modest reduction in mortality in multi-organ failure
• Moderate doses of hydrocortisone seems to increase blood pressure and increase survival