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Clinical Micro > Anaerobes > Flashcards

Anaerobes Flashcards

1
Q

What are 3 possible reasons why an anaerobe cannot grow in the presence of oxygen?

A

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

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2
Q

Most clinical isolates are what form of anaerobe? what do they have small amounts of?

A

moderately obligate anaerobes

have small amount of both catalase and superoxide dismutase.

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3
Q

What are the three methods for excluding oxygen in bacterial culture?

A
  1. Liquid media containing fresh animal tissue or 0.1% agar containing a reducing agent, thioglycollate
  2. Anaerobic jar using gas packs or gas replacement system
  3. Anaerobic chamber
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4
Q

Which of the methods is most commonly used by labs?

A

Anaerobic jar

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5
Q

What is used as an indicator in anaerobic jars for the presence of oxygen?

A

Methylene blue - will remain blue if oxygen is present

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6
Q

What two species of anaerobes are endogenous to the skin?

A

Propionibacterium, Peptostreptococcus

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7
Q

How are anaerobes able to live on the skin? (2 reasons)

A
  1. Aerobes consume O2 and lower the Redox potential2. Anaerobes live in microfissures / biofilm
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8
Q

What species of bacteria tend to inhabit the upper respiratory tract

A

Propionibacterium

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9
Q

What species of anaerobic bacteria inhabit the mouth? what % of mouth bacteria are anaerobes?

A

Fusobacterium, Actinomyces

90%

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10
Q

What species of anaerobic bacteria inhabit the GI tract?

A

Bacteroides and Fusobacterium

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11
Q

What species of anaerobic bacteria inhabit the vagina?

A

Lactobacillus

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12
Q

Wiping out endogenous flora with antibiotics heavily favours the growth and development of..?

A

Anaerobes

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13
Q

What are 2 ways in which Anaerobes contribute to host physiology?

A
  1. Prevent colonization of invading pathogens
    - Prevent attachment, decrease pH, nutrient robbing, toxic metabolites
  2. Production of metabolites like B. fragilis synthesizing vitamin K and conjugating bile acids
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14
Q

If someone has an anaerobic infection, the source of the infection tends to be..?

A

usually the endogenous flora of host

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15
Q

What are 3 common features of an anaerobic infection?

A
  1. Abscess forming
  2. Formation of exotoxins
  3. Tend to be polymicrobial
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16
Q

What are 6 factors that predispose patients to developing an anaerobic infection?

A
  1. Trauma to mucous membranes/skin
  2. Interruption of blood flow
  3. Tissue necrosis
  4. Decrease in redox potential in tissue
  5. Prior antibiotic treatment
  6. Immunosuppression
17
Q

What are 6 virulence factors that anaerobes might have?

A
  1. Polysaccharide capsule
  2. Adherence factors
  3. Toxins (some can be necrotizing)
  4. Hyaluronidase
  5. Lipases
  6. Enzymes- i.e. proteases / phospholipases
18
Q

What are some indicators of an anaerobic infection?

A
  1. Foul smell
  2. Black discolouration
  3. Production of gas (crackling sound)
  4. Pus producing
  5. Close to mucosal surface
  6. Persistence of infection despite antibiotic treatment
19
Q

What are 4 types of specimins for anaerobic culture?

A
  1. Swab
  2. Aspirate
  3. Tissue
  4. Blood
20
Q

How long are the primary cultures allowed to incubate before examination?

A

48 hours

21
Q

What is done if no growth is observed after 48 hours?

A

The sample is re-incubated for up to 5 days

22
Q

What are 4 indications (in culture) that you are dealing with an anaerobe?

A
  1. Foul smell when you open the dish
  2. Double hemolysis observed
  3. Failure to grow in aerobic conditions
  4. Pigmented or fluorescent colonies
23
Q

What do you do if you observe growth under anaerobic conditions?

A
  1. Subculture anaerobically and aerobically to check if it’s a facultative anaerobe
  2. Gram stain suspicious colonies
    - ex: if you notice spore production you can be sure it’s either Clostridium (anaerobe) or Bacillus (aerobe)
24
Q

Is antimicrobial susceptibility typically done for anaerobes? Under what conditions?

A

no

Done for monomicrobial infections

25
Q

What is the anaerobic drug(s) of choice?

A

Metronidazole, as well as Amox-clav / Pip-tazo

26
Q

What are 3 treatment protocols for anaerobic infections?

A
  1. Surgical intervention (draining of source or removal of necrotic tissue)
  2. Antibiotics
  3. Antitoxins

Clinical Micro (28 decks)

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