Anaerobic bacteria

Question 1

Why are most infections by anaerobes mixed, opportunistic infections that may include boy aerobic and anaerobic bacteria?

Answer 1

The aerobes metabolize O₂ making the environment more favorable for the anaerobes.

Question 2

Why are anerobes sensitive to O₂ intermediates? (3 points)

Answer 2

1. They have little superoxide dismutase to remove O₂ radicals.
2. They have low amounts of catalase to remove H₂O₂
3. They often lack cytochromes

Question 3

Most intra-abdominal infections are a result of what organism?

Answer 3

Bacteroides fragilis

Question 4

What is the structure/morpholic features of Bacteroides fragilis?

Gram-stain
Presence or lack of capsule

Answer 4

They are gram negative anaerobes the possess a capsule

Question 5

1. Where are the predominant sites of infection for Bacteroides fragilis?
2. Why are Bacteroides (and other anerobic) infections foul smelling?
3. What is a major bi-product of fermentation metabolism?

Answer 5

1. Colon (Intra-abdominal abcess), mouth, and skin
2. Due to short chain fatty acids produced during fermentation
3. Gas

Question 6

What are the elements that promote virulence for *Bacteroides fragilis? *What is the function of each feature?

Answer 6

1. Polysaccharide capsule – prevents phagocytosis
2. Aerotolerant – able to creat infection in presence of atmospheric O₂
3. Encodes two major oxidative stress genes – tissue damage

Question 7

What are the common characteristics of all Clostridium species?

Aerophilicity
Gram stain
Spore forming

Answer 7

All *Clostridium *are anaerobic, gram positive, spore forming bacilli.

Some species are aerotolerant.

Question 8

Bacteroides fragilis and Clostridium species are both anaerobic. What most obviously separates them for identification?

Answer 8

Bacteroides is gram negative and Clostridium is gram positive

Question 9

What type of disease does C. difficile typically create and by what means?

Answer 9

Gastrointestinal disease by Exotoxins A and B

Question 10

1. How is C. difficile transmitted/acquired?
2. When does it cause disease?

Answer 10

1. Fecal-Oral ingestion of endospores
2. It is part of normal flora but causes disease in a compromised host – Primarily antibiotic associated

Question 11

What is C. difficile’s motility status?

Answer 11

It is motile via flagella (H-antigen positive)

Question 12

1. How does the C. difficile toxins create diarrhea and damage to colonic epithelia cells?
2. C. diff. secretes two toxins, A and B. Which causes the diarrhea and which causes epithelia damage?

Answer 12

1. Glycosylation of Rho GTPases → Actin depolymerization → disruption of epithelial cells → diarrhea.
2. A causes diarrhea and B causes cytotoxic damage to epithelia cells.

Question 13

How is C. diff. treated?

Answer 13

Metronidazole and Oral vancomycin along with termination of previously responsible antibiotic

Question 14

What Clostridium species is associated with Histotoxicosis?

What else is it primarily responsible for?

Answer 14

Clostridium perfringens

It is also the culprit fo the majority of Clostridia-mediated myonecrosis after a deep wound to muscle.

Question 15

1. What toxin creates most of the damage of C. perfringens?
2. How does its toxin create damage?
3. What clinical condition results from this damage?

Answer 15

1. Alpha toxin
2. It reduces tissue redox potential creating host cell death.
3. Alpha toxin produces gas gangrene

Question 16

What treatment is required for C. perfringens infection with gas gangrene or myonecrosis

Answer 16

Antibiotics AND Excision/Amputation of tissue

Question 17

How does C. tetani create its systemic effects?

Answer 17

The toxin it produces spreads throughout the body while the bacteria remains at the initial site of infection.

Question 18

What is the difference between the paralysis created by C. tetani vs. C. botulinum?

Answer 18

Tetanus creates a spastic paralysis and Botulism creates a flaccid paralysis

Question 19

What are the similarities and differences between the tetanus toxin and the botulism toxin in terms of their functionality?

Answer 19

They both have an A:B structure and cleave SNARE proteins.

TeNT inhibits interneuron function
while
BoNT inhibits release of pre-synaptic Acetylcholine

Question 20

What is the treatment for C. tetani infection?

Answer 20

Prevention is the only treatment:

1. Vaccinate
2. Administer anti-biotics for bacteria
3. Administer anti-TT antibody for the toxin

Question 21

What are the most common natural forms of C. botulinum?

Answer 21

A, B, and E serotypes

Question 22

How can C. botulinum be acquired?

Answer 22

1. Toxin ingestion from spoiled food
2. Spore ingestion
3. Spore in wound

Question 23

What is the prevention/treatment for botulinum infection?

Answer 23

There is no vaccine.

Passive immunity can be given through anti-toxin. CDC has anti-A,B,E and Army has anti-A-G

Primarily though supportive care is only option.