Bacillus anthracis

Background

Microbiology

• Gram-positive bacillus that is distinguished from other Bacillus by being non-motile and non-hemolytic
• Colonies are gray, flat, and may have a "Medusa head" or "comet" appearance
• The main toxin has subunits A and B
  • A subunit may be either EF (edema factor) or LF (lethal factor)
  • B subunit is the protective antigen, against which antibodies react
• Lives in soil
• Wild and farm animals that have contact with contaminated soil is a common exposure, including to wool and animal hides
• Can also be acquired by inhalation of spores

Clinical Manifestations

Cutaneous Anthrax

• Caused by inoculation of spores into soft tissue
• Incubation period of 2 to 5 days
• Lesion develops at site of inoculation, starting as erythemaous papule, then ulceration, then eschar
• May progress to sepsis

Pulmonary Anthrax

• Caused by inhalation of spores
• Also known as woolsorter's disease
• Start with malaise, fever, and nonproductive cough, followed by respiratory distress, severe pulmonary edema, and death

Gastrointestinal Anthrax

• Caused by ingestion of spores
• Infects oropharynx or abdomen
• Causes sepsis

Management

• Inhalational anthrax: ciprofloxacin 400 mg IV q12h ± a second antibiotics
• Cutaneous anthrax (mild): ciprofloxacin 500 mg p.o. q12h, doxycycline 100 mg p.o. q12h, or amoxicillin 500-1000 mg p.o. q8h
  • Duration typically 7 to 10 days (naturally acquired) or 60 days (bioterrorism-related)
• Meningitis: ciprofloxacin plus meropenem plus linezolid
  • Duration 2-3 weeks, then prophylaxis to complete 60 days
• Almost universally susceptible to ciprofloxacin and doxycycline1
• Generally susceptible to penicillin, though should wait for susceptibility results before using
• Often resistant to extended-spectrum β-lactams such as ceftriaxone and ceftazidime, as well as aztreonam and TMP-SMX