questions 2

Bacillus anthracis

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Topic updated on 01/30/17 1:48am

Snapshot
  • A 60-year-old postal worker presents to ED with the chief complaint of a dry cough for 5 days associated with fever, malaise, dyspnea on exertion, and pleuritic chest pain. There is no history of recent travel or contact with sick persons. Temperature is 102.5°F (39°C), blood pressure is 140/80mmHg, pulse is 100/min, respirations are 18/min, and oxygen saturation is 97%. Chest exam reveals an ill-looking man with bilateral rhonchi heard in the lung bases. Chest radiograph reveals a widened mediastinum and bilateral infiltrates. Blood cultures grew Gram-positive bacilli with a box-car appearance. 
Introduction
  • Classification
    • bacteria
      • gram-positive bacilli
        • spore-forming
          • Bacillus
            • Bacillus anthracis
  • Pathogenesis
    • transmission
      • inhalation of spores (anthrax)
      • contact with infected animals (e.g., livestock or animal hide handling)
    • reservoir
      • animals
      • skin
      • soil
    • molecular biology 
      • polypeptide capsule is immunogenic and antiphagocytic
        • the only bacterium with a polypeptide capsule
        • contains D-glutamate
      • anthrax toxin has 3 components
        • protective antigen
        • lethal factor
        • edema factor
          • mimics the activity of adenylate cyclase (cAMP)
          • responsible for edematous borders of black eschar
Diseases
  • Anthrax
    • cutaenous anthrax
      • contact → black eschar (painless ulcer)
        • eschar is surrounded by edematous ring 
        • caused by lethal factor and edema factor
      • can progress to bacteremia and death
    • pulmonary anthrax
      • inhalation of spores → flu-like symptoms
      • rapid progression to fever, pulmonary hemorrhage, mediastinitis, shock, and death
        • near 100% mortality
      • sometimes called woolsorters' disease 
        • spores inhaled from contaminated sheep or goat skin/wool
    • GI anthrax
      • rare
Evaluation
  • Aerobic
  • Spore-forming rods
  • Serpentine or "medusa-head" appearance on microscopy
  • Large and "boxcar-like"
  • Diagnose with Gram stain and blood culture
  • Widened mediastinum on CXR
Differential
  •  Cutaneous
    • bubonic plague
    • lymphocutaneous tularaemia
    • primary syphillis
  • Pulmonary anthrax
    • pneumonia
    • influenza
Treatment
  • Ciprofloxacin
  • Doxycycline
  • Toxoid vaccine to prevent
    • known as AVA (acellular vaccine adsorbed)
Prognosis, Prevention, and Complications
  • Prognosis
    • good if treated early with antibiotics
    • worse if pulmonary disease
  • Prevention
    • post-exposure prophylaxis
      • ciprofloxacin or doxycycline
      • vaccination with AVA
      • monoclonal antibodies if alternative therapies not tolerated
  • Complications
    • bacteraemia leading to sepsis
    • meninigitis


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Qbank (2 Questions)

TAG
(M1.MC.75) A 65-year-old farmer presents for evaluation of a lesion on his arm. The lesion originally started as a painless pruritic papule, but enlarged over the last several days. The current appearance of the lesion is shown in Figure A. Which of the following is the most likely cause of the lesion? Topic Review Topic
FIGURES: A          

1. Autoimmune disorder against hemidesmosomes
2. S. aureus infection
3. B. anthracis infection
4. Squamous cell carcinoma
5. Basal cell carcinoma

PREFERRED RESPONSE ▶
TAG
(M1.MC.4754) A 61-year-old male presents to the emergency department complaining of malaise. He reports a two-day history of rapidly progressive fatigue, malaise, fever, and dyspnea. The patient immigrated from Finland five years ago and works on a large farm. His past medical history is notable for diabetes mellitus and emphysema. He takes metformin, salmeterol, and tiotropium. He has a 40 pack-year smoking history. His temperature is 102.3°F (39.1°C), blood pressure is 90/50 mmHg, pulse is 130/min, respirations are 30/min, and oxygen saturation is 92% on room air. Physical examination is notable for rales at the bilateral lung bases. Chest radiography reveals a widened mediastinum and bilateral pulmonary infiltrates. He is subsequently admitted and started on broad-spectrum antibiotics and fluid resuscitation. However, his fever rapidly progresses and he perishes the following day. Results from a blood culture taken on admission are shown in Figure A. The pathogen responsible for this patient’s condition produces a toxin with which of the following mechanisms of action? Topic Review Topic
FIGURES: A          

1. Directly activates adenylyl cyclase
2. Mimics adenylyl cyclase
3. Inhibits 60S ribosomal subunit
4. Binds Fc portion of immunoglobulin
5. Depolymerizes actin cytoskeleton

PREFERRED RESPONSE ▶


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