46. Anaerobes II Flashcards
anaerobic spore-forming GP rods?
C.diff C.perfiringens C.tetani C.botulinum C.sordellii C.septicum
C. tetani general characteristics?
anaerobic spore-forming GP rods
- obligate anaerobe
- spores in GI tracts of animals and soil
C.tetani pathogenesis and virulence?
- intro into body via puncture wounds (dirty nail, dirty needles in IVDU)
- contaminated surgical procedures (umbilical stump post unsterile delivery, surgery for necrotic bowel infection)
- spores germinate and vegetative from produces tetanospasmin (tetanus toxin) at site of inoculation
- unregulated excitatory synaptic activity = spastic paralysis
tetanospasmin (tetanus toxin):
- 2 peptides (A-B toxin)
- B subunit binds sialic acid receptors of motor neurons leading to internalization of smaller A subunit in vesicles
- retrograde axonal transport via motor nerves to anterior horn cells or brainstem
- is a zinc-dependent protease that cleaves proteins necess for release of inhibitory neurotrans (GABA and Gly)
C.tetani disease, dx and tx?
Generalized tetanus
- involvement of the masseter: trismus (lockjaw/risus sardonicus)
- generalized contractions of back muscles (opisthotonos)
- autonomic instability
- contracture of thoracic and pharyngeal muscles: apnea, airway obstruction, dysphagia
Localized tetanus
- site of spore inoculation
Cephalic tetanus
- injuries to head or neck
Neonatal tetanus
- dirty umbilical stump, unvaccinated mother
- unsterile delivery field
- trismus, inability to nurse, rigidity, apnea
dx: Clinical history + physical exam (don’t use culture or microscopy because worry about toxins, not organism, and hard to detect toxin or Abs vs toxin)
tx:
- clean wound
- metronidazole
- intramuscular tetanus IgG (at site of inoculation)
- tetanus vaccine at a different site
- maintain airway, treat hemodynamic instability, administer sedatives, muscle relaxants (ICU)
C. botulinum characteristics?
anaerobic spore-forming GP Rod
- obligate anaerobe
- ubiquitous in soil, marine sediment, surfaces of fruit, veggies, seafood
C. botulinum pathogenesis and virulence?
- affects peripheral voluntary and autonomic cholinergic receptors
- flaccid paralysis
- toxin = heat-labile metalloproteinase, but resistant to degradation by enzymes of GI tract
- inhibits release of Ach at NMJ
C. botulinum disease, dx, and tx?
Foodborne botulism
- home-canned food w/alkaline pH (veggies, not fruit)
- home-preserved/ fermented fish
- pruno (fermented potato drink in jail)
- home-fermented tofu
Wound botulism
- black tar heroin injected subQ or IM
- other puncture wounds
Infant botulism
- colostrum in breast milk provides immunity
- weaned from breastmilk and injest spores (not toxin)
- Infant GI tract susceptible to colonization
- wild honey or home-canned foods, env’t dust ingestion
- poor feeding, hypotonia, drooling, ptosis
Inhalational botulism
- aerosolized – bioterrorist attack
- super potent!
dx: history and physical exam
- cardinal clinical sign = cranial neuropathies w/symmetric, descending paralysis progressing to respiratory failure
- no sensory deficits or unresponsiveness
- fever = rare
- autonomic deficits: hypothermia, hypotension, GI dysfunction
- botulinum toxin may be present in food, feces, or serum
tx:
- ventilator support, metronidazole, and trivalent botulinum antitoxin
- prevented by maintaining food at acid pH or at 4C or colder. Preformed toxin is destroyed by heating to 80C for 20 min
C. perfrinogens general characteristics?
anaerobic spore-forming GP rods
- Rarely form spores
- found worldwide in soil, water and GI tracts of humans&animals
- most commonly isol clostridial species
- large, rectangular rods w/spores rarely seen (polymicrobial infections)
- relatively aerotolerant and grows rapidly
- double zone of hemolysis
C. perfringens virulence?
- multiple toxins and hemolytic enzymes
- food poisoning due to heat labile enterotoxin
C. perfringens disease, dx, tx?
- Food poisoning primarily w/contaminated meat products causes self-limiting watery diarrhea (6-24 hours)
- Soft tissue infections: cellulitis, fasciitis (suppurative myositis), myonecrosis (gas gangrene): life-treatening, rapidly-progressive infection, major and minor lethal toxins, complication of trauma or surgical wound, presents initially w/severe pain then progresses to edema, pallor & may have hemorrhagic bullae, subQ emphysema, gas seen on radiographic imaging
- bacteremia: half of the blood isolates are clinically insignificant
dx:
- microscopy: bacteria frequently observed
- culture is rapid & sensitive
tx:
- prompt, aggressive use of surgery and Abx
- pcn is uniformly active, used in combo w/clindamycin (inhibits toxin synthesis)
C. diff general characteristics?
anaerobic spore-forming GP rods
- colonizes GI tract in small # healthy ppl
- vegetative cells really sensitive to O2 toxicity
- spores observed on gram stain
- major cause of HA-infections
C. diff pathogenesis and virulence?
- suppression of normal flora w/Abx leads to overgrowth
- enterotoxin
- cytotoxin
C.diff disease, dx, tx?
- community-acquired infections w/a new strain that produces high levels of toxin becoming common
- abx-assoc diarrhea
- pseudomembranous colitis
dx:
- PCR amplification of toxin genes (sensitive and rapid but NOT specific for infection if pt is colonized)…so only diagnostic if pt is symptomatic
- dog trained to sniff out C.diff
- megacolon
tx:
- discontinuation of the implicated Abx
- metronidazole for non-severe disease
- PO vanco +/- IV metronidazole for severe disease
- disinfect room re: spores
- cut out megacolon
- transpusion
