Anaerobes- Steinauer Flashcards
What are the basic characteristics of anaerobes?
- Don’t grow in presence of oxygen.
• Strict anaerobes: dies immediately when exposed to oxygen.
• Aerotolerant: can survive brief exposure of oxygen. - Get energy thru fermentation.
- Grown in thioglycollate broth which consumes oxygen or in anaerobic chamber.
Why is oxygen toxic?
- Autoassassination: toxic derivatives of oxygen as byproduct of metabolism.
• May or may not have special enzymes for metabolism of ROS (superoxide dismutase and catalase). - Oxygen has high oxidation-reduction potential.
• May react directly w/ sensitive targets, oxidizing them to a non-functional form.
What are the potentially pathogenic anaerobes that are part of our normal flora (endogenous)? Where are they found?
- Bacteriodes- colon
- Fusobacterium- vagina, mouth, colon
- Porphyromonas- mouth
- Prevotella- vagina
- Actinomyces- mouth, vagina
- Propionibacterium- skin
- Peptostreptococcus- skin, colon, mouth
What are the characteristics of endogenous anaerobic infections?
- Proximity to colonized mucosa.
- Tissue necrosis or abscesses.
- Foul-smelling discharge (due to fatty acids).
- Typically mixed infections.
- Presence of gas in infected tissue.
- Anaerobic culture and difficult to grow.
- Don’t respond to aminoglycosides (respond to clindamycin and metronidazole).
What are the characteristics of Bacteriodes? What is the species we are concerned with?
- Gram- rods (little rounder shape though = coccobacillus)
- Found in colon and mouth.
- Resistant to aminoglycosides gentamicin and kanamycin and PCN.
•Clindamycin and metronidazole are effective though. - Account for intra-abdominal, lung, brain and pelvic abscesses.
Example: Bacteroides fragilis
What are the characteristics of Bacteroides fragilis? What does an infection cause? What are the virulence factors? What is it associated with?
•Obligate anaerobe, non-motile, non-spore forming
•Complex of species.
•Bowel flora.
•Intra-abdominal infections (after surgery or trauma)
Virulence factors:
1. Polysaccharide capsule: antiphagocytic and promote abscess formation.
2. PCN resistant and aminoglycoside resistant.
3. LPS (but weak endotoxicity)
4. Aerotolerant (produces SOD and catalase)
5. Enzymes: lipase, proteases and cytolysins.
6. Some produce enterotoxin: BF Toxin = diarrheal disease in children.
•Assoc. w/ intra-abdominal, lung, brain and pelvic abscesses.
What are the characteristics of Prevotella and Porphyromonas?
o Produce black iron pigments when gown on blood agar.
o Found in mouth and vagina (Prevotella).
o Can cause infections of the head, neck and respiratory tract as well as chronic periodontitis (porphyromonas gingivalis)
What are the characteristics of Fusobacterium?
o Normal oral flora.
o Has normal LPS: induces septic shock and vascular collapse.
o Leads to ANUG-trench mouth.
What are the characteristics of Peptococcus and Peptostreptococcus?
o Anaerobic Gram-positive cocci
o Found in the mouth, skin, gastrointestinal, vagina, and urinary tract.
What are the characteristics of Propionibacterium acnes?
o Gram+ anaerobic rod
o Assoc. with the inflammatory process in acne lesions.
What are the characteristics of Actinomycetes?
o Gram+ rods and have long branching filaments.
o Forms lesions that are hard, nontender swellings that drain pus through sinus tracts. Hard, yellow granules often form in the associated pus. Infection is often associated with IUDs.
What are the characteristics of Clostridium? What are the 4 species we care about? Which one is an endogenous anaerobe?
- Gram-positive rods (Bacillus, Corynebacterium, Listeria)
- Spore forming (Bacillus)
- Found in soil as well as the GI of humans and animals.
- Protein exotoxins (Bacillus, Corynebacterium)
• Diseases most commonly caused by wounds or ingestion of toxin.
Species: C. tetani, C. perfringens, C. botulinum, C. difficile (ENDOGENOUS!)
What does C. tetani cause? What are its characteristics? What is its pathogenesis? What is the treatment? Vaccine?
Causes: tetanus
Rods w/ spores on the end.
Frosted appearance on blood agar.
Pathogenesis due to toxin (tetanospasmin):
o Neurotoxin.
o Attacks inhibitory neurons.
o Convulsive contraction of voluntary muscles (spastic paralysis). (lock jaw, arching of back)
o Binds to peripheral nerves → spinal cord
Antitoxin: human tetanus immune globulin (HTIG)
Vaccine: DTaP
What does C. perfringens cause (2)? Describe each.
- Gas Gangrene–Wound and soft tissue infections
Spores contaminate and germinate
Gas from fermentation
Necrotizing toxins (12)
Septic Shock
Treatment: remove bad tissue and give antibiotics.
2. Food poisoning Diarrhea without fever or vomiting Enterotoxin Rich meat dishes kept warm •(Spores germinate)
What does C. botulinum cause (3)? What is the pathogenesis?
Botulism
1. Food poisoning- Consumption of toxin (home-canned food)
2. Wounds- Spores enter wound and produce toxin
3. Infant botulism- C. botulinum establishes in GI tract of infant and produces toxin, honey (may have spores). Less severe. They appear lethargic, feed poorly, constipated and weak cry. “Floppy baby syndrome.”
Pathogenesis due to botulinum toxin:
o Neurotoxin.
o Acts at neuromuscular junctions to block release of ACh.
o Leads to flaccid paralysis and respiratory failure.
o Toxin is heat labile.
