46. Anaerobes II Flashcards Preview

HDID 2 > 46. Anaerobes II > Flashcards

Flashcards in 46. Anaerobes II Deck (13):
1

anaerobic spore-forming GP rods?

C.diff
C.perfiringens
C.tetani
C.botulinum
C.sordellii
C.septicum

2

C. tetani general characteristics?

anaerobic spore-forming GP rods

- obligate anaerobe
- spores in GI tracts of animals and soil

3

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)

4

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)

5

C. botulinum characteristics?

anaerobic spore-forming GP Rod

- obligate anaerobe
- ubiquitous in soil, marine sediment, surfaces of fruit, veggies, seafood

6

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

7

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

8

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

9

C. perfringens virulence?

- multiple toxins and hemolytic enzymes
- food poisoning due to heat labile enterotoxin

10

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)

11

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

12

C. diff pathogenesis and virulence?

- suppression of normal flora w/Abx leads to overgrowth

- enterotoxin
- cytotoxin

13

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