Anaerobic Bacteria Flashcards
Obligate Aerobes
Bacteria that rely on oxygen for their electron transport pathway for ATP generation. Cannot grow or quickly die without oxygen.
Obligate Anaerobes
Bacteria that lack superoxide dismutase and/or catalase enzymes and also lack pathways to regenerate enzymes that have become oxidized. They use fermentation pathways rather than electron transport to generate ATP. Cannot grow or quickly die in the presence of oxygen.
Facultative Anaerobes
Some bacteria encode both fermentation pathways and electron transport pathways to generate ATP so that they can use oxygen when it’s available and fermentation when it’s not. Usually grow faster in the presence of oxygen.
2 major methods of anaerobic pathogenesis
- Normal flora gone wrong- escape from normal compartment, can form abscesses
- Soil- Entry through wounds, entry through food.
Anaerobic culture techniques
For any technique the samples must be stored under anaerobic conditions and transported quickly.
- Liquid culture- add reducing agent, fill tube completely, stopper tightly, incubate without shaking.
- Agar plates- streak quickly, place in anaerobic culture jar, add a chemical system to bind oxygen, incubate whole jar 48h, if working further with colonies research open in an anaerobic glovebox.
- Can also use gas chromatography to analyze the organic acids being produced by the anaerobe’s fermentation pathway.
Treatment of anaerobic infection in the form of an abscess
Surgical care- drain, debride, followed by antibiotics
Treatment of a toxigenic anaerobe
Antitoxin, followed by antibiotics
Examples of anaerobic normal flora that can cause infection
Mouth flora: Actinomyces, B. corrodens, P. melaninogenica
Colon and vagina: B. fragilis
Examples of soil anaerobic bacteria that often enter through wounds
C. tetani
C. perfringens in gas gangrene
C. botulinum in wound botulism
Can produce exotoxins
Examples of soil anaerobic bacteria that can enter through vacuum packaged foods
C. perfringens in food poisoning: bacteria briefly survive in gut and release enterotoxin
C. botulinum in infant botulism: bacteria briefly survive in gut and release neurotoxin
C. botulinum in foodborne botulism: bacteria do not survive in gut, but have already filled food with neurotoxin
Methods of identifying anaerobes
- Gram staining
- Chemical testing
- Gas chromatography
Features of Clostridium
Gram +
Rods
Form spores
Features of Bacteroides
Gram -
Rods
No spores
Features of Prevotella
Gram -
Rods
No spores
Features of Actinomyces
Gram +
Long, filamentous rods
No spores
C. tetani Features
Reservoir-soil Disease-tetanus Primary virulence factor-tetanospasmin Gram + Fast acting and nonspecific
C. botulinum features
Reservoir-soil
Disease-botulism
Primary virulence factor-botulinum toxin
C. perfringens features
Reservoir- soil
Disease- gas gangrene or food poisoning
Primary virulence factor- tissue degrading enzymes or enterotoxin
C. difficile features
Reservoir- normal flora
Disease- pseudomembranous colitis
Primary virulence factor- exotoxins A and B
Gram +, spore forming rods
Fecal-oral transmission, common in hospitals
GNAB features
Reservoir- normal flora
Disease- abscesses
Primary virulence factors- tissue degrading enzymes, capsule
Actinomyces features
Reservoir- normal flora
Disease- Actinomycosis (abscess)
C. tetani pathogenesis
Insertion beneath skin surface limits air contact
Spores germinate
Vegetative cells release exotoxin tetanospasmin
C. diff pathogenesis
Recent course of antibiotics or cancer chemotherapeutics suppresses other normal flora, allows C. difficile to overgrow
Germinating cells release Exotoxin A, which disrupts tight junctions, causing intestinal swelling and inflammation
Exotoxin B is the major toxin, disrupts the cytoskeleton by depolymerizing actin, kills the surrounding cells
A more virulent and drug-resistant strain of C. difficile emerged in 2001-2002; cases doubled 2000-2003 and have continued to rise since
Mortality has increased from 6%
