Updated: 6/18/2018

Bacillus anthracis

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  • A 35-year-old woman presents to the emergency room for an ulcer on her arm. She reports that she recently completed a travel program in Africa, where she worked on the farms in exchange for room and board. She reports coming into contact with farm animals every day. She said she accidentally cut her left forearm on some wooden post a few days ago. Yesterday, she noticed a painless but pruritic lesion. On physical exam, there is a 4-mm papule with a dusky-looking central vesicle and surrounding edema. There is also axillary lymphadenopathy. She is started on antibiotics.
  • Classification
    • Bacillus anthracis
      • spore- and exotoxin-forming gram + rod
      • capsule protects against phagocytosis
        • the only bacteria with a polypeptide capsule (poly-D-glutamate)
    • transmission
      • inhalation of spores
      • introduction of spores into a skin break
      • ingestion of spores
  • Epidemiology
    • incidence
      • more common in areas where animal vaccination rates are low
      • bioterrorism
    • risk factors
      • intravenous drug use (e.g., heroin)
      • occupational exposure to unvaccinated animals
      • occupational exposure to animal hides
  • Pathogenesis
    • anthrax toxin composed of 3 components
      • protective antigen
        • binds cell surface and mediates entry of edema and lethal factor
      • edema factor 
        • binds calmodulin and performs the same function as adenylate cyclase, ↑ cAMP and resulting in
          • black eschar’s edematous borders
          • vasodilation and hypotension
      • lethal factor
        • a protease that cleaves the amino terminus of mitogen-activated protein kinase kinases (MAPKK), inhibiting this signalling pathway, and resulting in macrophage apoptosis
    • infection may spread via lymphatics
  • Associated conditions
    • cutaneous anthrax
      • most common
    • pulmonary anthrax
      • “woolsorter’s disease”
    • gastrointestinal anthrax
  • Prevention
    • post-exposure prophylaxis
      • 3 doses of anthrax vaccine
      • 60 days of a single antibiotic
        • ciprofloxacin or doxycycline are first line
  • Prognosis
    • biphasic nature of pulmonary anthrax
      • prodromal symptoms
      • fulminant bacteremic phase
        • often leads to death within days
  • Symptoms
    • pulmonary anthrax
      • flu-like syndrome with non-productive cough
      • nausea and vomiting
      • hemoptysis
      • chest pain
    • gastrointestinal anthrax
      • nausea and vomiting
      • dysentery
      • abdominal pain
  • Physical exam
    • cutaneous anthrax  
      • initial lesion is a painless and pruritic papule with a central vesicle or bulla
      • this progresses to painless and necrotic black eschar
        • surrounded by edema
      • eschar sloughs off at day 14
    • pulmonary anthrax
      • mediastinitis
      • shock
      • hypoxia
      • dyspnea
    • lymphadenopathy
  • Chest radiography
    • indication 
      • pulmonary anthrax
    • findings
      • pleural effusion
      • pulmonary consolidation
      • widened mediastinum
  • Labs
    • multiple methods of detection
      • “medusa head” appearance on microscopy
        • halo of projections
      • culture of blood, pleural fluid, or eschar
      • positive Gram stain of affected tissue
      • polymerase chain reaction
      • anti-protective antigen immunoglobulin G on enzyme-linked immunosorbent assay
      • biopsy with immunohistochemistry staining
    • marked hemoconcentration
  • Making the diagnosis
    • most cases are diagnosed clinically and confirmed with
      • positive culture, serology, or immunohistochemistry
      • detection of Bacillus anthracis DNA in tissue
  • Community-acquired pneumonia
    • distinguishing factor
      • less likely to have nausea, vomiting, pallor, or unexplained mediastinal widening on chest radiography
  • Management approach
    • antibiotics should be given in the prodromal phase of the disease
    • cutaneous anthrax can be treated with 1 antibiotic
    • systemic anthrax can be treated with 2 antibiotics
  • Medical
    • ciprofloxacin or doxycycline
      • indication
        • all patients
    • protein synthesis inhibitor
      • indications
        • systemic anthrax
        • combination therapy with fluoroquinolone or doxycycline
      • mechanism
        • reduces toxin production
      • drugs
        • clindamycin
        • linezolid
    • antitoxins
      • indication
        • all patients
      • drugs
        • monoclonal antibodies
          • raxibacumab
        • anthrax immunoglobulin
  • Bacteremia from cutaneous anthrax
  • Death

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Questions (3)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2

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(M1.MC.17.4754) 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? Review Topic | Tested Concept

QID: 108945

Directly activates adenylyl cyclase




Mimics adenylyl cyclase




Inhibits 60S ribosomal subunit




Binds Fc portion of immunoglobulin




Depolymerizes actin cytoskeleton



L 1 C

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(M1.MC.15.75) 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? Review Topic | Tested Concept

QID: 106723

Autoimmune disorder against hemidesmosomes




S. aureus infection




B. anthracis infection




Squamous cell carcinoma




Basal cell carcinoma



L 2 E

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