Bacillus and Clostridium Species

Gram-Positive Spore-Forming Bacilli

• Bacillus and Clostridium species are ubiquitous and can survive in the environment for many years due to their ability to form spores.

Bacillus

• Large, aerobic, gram-positive rods occurring in chains.
• Spores are centrally located.
• Saprophytic organisms, ubiquitous in soil.

Bacillus anthracis

• Causes fatal sepsis in grazing mammals, such as cattle and sheep.
• Characterized by Medusa-head (curled hair) colonies.
• Poly-D-glutamic capsule, unusual because it's composed of amino acid residues, not polysaccharide.
• Capsule can be detected by the McFadyean reaction.
• Produces protective antigen (PA) that combines with edema factor (EF) and lethal factor (LF) to form toxins.
• Enters humans through injured skin, mucous membranes, and inhalation of spores into the lungs.

Clinical Disease

• Cutaneous anthrax: results from contact with material containing anthrax endospores, over 90% of anthrax cases.
• Characterized by a pruritic papule with a central black eschar.
• Gastrointestinal anthrax: rare form of anthrax, caused by ingestion of undercooked food containing anthrax endospores.
• Symptoms: abdominal pain, vomiting, and bloody diarrhea.
• Inhalation anthrax (Woolsorter’s disease): most dangerous form of anthrax.
• Causes hemorrhagic necrosis, edema of mediastinum, substernal pain, pronounced mediastinal widening, hemorrhagic pleural effusions, and sepsis.

Prevention and Treatment

• AVA BioThrax vaccine: 0.5 mL I.M. at 0 and 4 weeks, then at 6th, 12th, 18th months, then annual booster.
• Treatment: Ciprofloxacin, Pen G with Gentamicin or Streptomycin.
• Prophylaxis: Ciprofloxacin/Doxycycline with vaccine for 4 weeks, without vaccine for 8 weeks.

Bacillus cereus

• Part of the normal flora of the human intestine.
• Usually found in grains like rice.
• Characterized by “swarming movement” in semisolid culture media.
• Produces an enterotoxin that causes food poisoning.
• Heating food does not always kill the spores, which germinate as the food cools.
• Causes:
  • Emetic type: nausea, vomiting, abdominal cramps, and diarrhea.
  • Diarrheal type: profuse diarrhea with abdominal pain and cramps.
  • Eye infections: severe keratitis, endophthalmitis, and panophthalmitis.
  • Endocarditis, meningitis, osteomyelitis, and pneumonia.
• Treatment: usually self-limiting, but in severe cases, oral rehydrating salt (ORS) can be used to prevent dehydration.
• For penicillin-resistant strains, use Vancomycin or Clindamycin with or without an aminoglycoside.