Anaerobes

Question 1

3 ways to determine MIC

Answer 1

E test
Agar dilution
Broth microdilution

Question 2

How does MacConkey stop the growth of gram positive organisms

Answer 2

Bile salts and crystal violet

Can get them without the crystal violet to allow for the growth of Strep

Question 3

Ecchymosis

Answer 3

Bruising not due to trauma

Blood pools under the skin

Question 4

Crepitus

Answer 4

Gas

Can press on the tissue and it sounds like you’re bursting bubbles

Question 5

2 clues to tell it is Clostridium perfringins on a microscope slide

Answer 5

1. Big gram positive bacilli

2. No neutrophils in sample (it produces a toxin that destroys leukocytes)

Question 6

What is the difference in paralysis between botulism and tetanus?

Answer 6

Botulism: flaccid paralysis
Tetanus: rigid paralysis

Question 7

3 possible mechanisms of why anaerobic bacteria cannot grow in the presence of oxygen

Answer 7

1. No cytochrome systems for the metabolism of O2
2. Little/no superoxide dismutase
3. Little/no catalase

Question 8

3 enzymes required for oxygen metabolism

Answer 8

Catalase
Superoxide dismutase
Peroxidase

Question 9

3 methods for excluding oxygen to grow anaerobes

Answer 9

1. Liquid media containing fresh animal tissue or 0.1% agar containing a reducing agent, thioglyocollate
2. Anaerobic jar: gas packs (has sodium bicarb and sodium borohydride that eat up all the oxygen) or gas replacement (computerized pump that sucks out all the air and replaces it with an inert gas)
3. Anaerobic chamber

Question 10

What colour is methylene blue with or without oxygen

Answer 10

Aerobic: blue
Anaerobic: colourless

Question 11

Do aerobes raise or lower the redox potential?

Answer 11

They consume O2 and LOWER the redox potential

Question 12

What does B. fragilis do? (2)

Answer 12

Synthesizes vitamin K

Conjugates bile acids

Question 13

6 Clinical features of anaerobic infections

Answer 13

1. Source is usually endogenous flora
2. Alterations of hosts tissue provides suitable conditions for opportunistic infections
3. Typically polymicrobial
4. Abscess formation
5. Exotoxin involvement
6. Smells really bad

Question 14

6 factors that predispose patients for anaerobic infections

Answer 14

Trauma to mucosal membranes or skin
Interruption of blood flow
Tissue necrosis
Decrease in redox potential in tissues
Prior antibiotic therapy
Immuno-suppression

Question 15

7 Anaerobic virulence factors

Answer 15

1. Polysaccharide capsule
2. Adherence factors
3. Toxins
4. Hyaluronidase
5. Lipases
6. Enzymes (ex: proteases, phospholipases)
7. Necrotizing toxins

Question 16

7 Indications of anaerobic infections

Answer 16

1. Usually purulent
2. Close proximity to mucosal surface
3. Infection persists despite antibiotic therapy
4. Presence of foul odor
5. Presence of large quantities of gas
6. Presence of black colour or brick red fluorescence
7. Distinct morphologic characteristics in gram stained preparation

Question 17

A double zone of hemolysis is typical for which organism?

Answer 17

Clostridium perfringins

Question 18

What two genera form spores? Are they aerobic or anaerobic?

Answer 18

Clostridium (anaerobic)

Bacillis (aerobic)

Question 19

Hyaluronidase function

Answer 19

Allows the bacteria to have disseminating infections

Breaks down connective tissue so it can spread