bacillus

• Bacillus


  Large gram-positive rods, arranged usually in long chains, form spores, aerobic, most members are saprophytic in water, soil, air and on vegetation
• Medically important Bacillus species

  • B. cereus
  • B. Subtilis
  • B. Anthracis
• Bacillus anthracis


  • Large bacilli (rods), gram positive, arranged as single or paired rods, or serpentine chains, spores located in the center, nonmotile, nonhemolytic
• Bacillus anthracis toxin proteins

  Protective antigen (PA), Edema factor (EF), Lethal factor (LF)
• Formation of Bacillus anthracis toxins

  1. PA + EF forms Edema toxin (EdTx)

  2. PA + LF forms Lethal toxin (LeTx)
• Bacillus anthracis virulence factors

  • Toxins
  • Capsule (polypeptide capsule)
• Bacillus anthracis clinical diseases

  • Cutaneous anthrax
  • Gastrointestinal anthrax
  • Inhalation anthrax
• Cutaneous anthrax


  Inoculation of Bacillus spores through exposed skin, from either contaminated soil or infected animal products, initially looks like insect bite, progresses to papule, vesicle, necrotic ulcer with central black eschar, may lead to sepsis, meningitis and death in 20% of patients
• Gastrointestinal anthrax


  Acquired by ingestion of soil or animal products contaminated with the spores, ulcers form at the site of invasion (mouth or esophagus), leading to regional lymphadenopathy, edema and sepsis, patient presents with abdominal pain, vomiting & bloody diarrhea, nausea, vomiting, malaise, fever which rapidly progress to systemic disease
• Inhalation anthrax


  Acquired by inhalation of the spores, called wool-sorter's disease, no person-to-person transmission, bacterial replication in mediastinal lymph nodes not in the bronchopulmonary tree, prolonged latent period up to 2 months or more, nonspecific symptoms of fever, myalgias, nonproductive cough, and malaise, progresses to shock and death within 3 days if left untreated, second stage is more dramatic with rapidly worsening course of fever, edema, massive enlargement of the mediastinal lymph nodes, respiratory failure, and sepsis, pneumonia rarely develops, meningeal symptoms in about half of patients
• Inhalation anthrax radiographic finding

  Widened mediastinum
• Bacillus anthracis laboratory diagnosis

  • Smear & microscopy
  • Culture
  • Other definitive identification tests
• Bacillus anthracis laboratory specimen collection

  • Cutaneous anthrax: fluid or pus
  • Inhalational anthrax (associated with sepsis): blood, pleural fluid, & CSF
  • Gastrointestinal anthrax: stool
• Bacillus anthracis microscopy


  Gram stain shows long, thin, gram-positive rods arranged singly or in long chains, spores not observed in clinical specimens but only in cultures incubated in low CO2 atmosphere
• Bacillus anthracis capsule demonstration

  Produced in vivo but not typically observed in culture, can be stained with India ink, methylene blue, or direct fluorescent antibody test, in vitro demonstration requires bicarbonate-containing medium, 5-7% CO2
• Bacillus anthracis colony characteristics

  Large, gray to white, nonhemolytic, dry, ground glass surface, rough texture (R), irregular edges with projections, comma-shaped outgrowths (Medusa head morphology), sticky
• Bacillus anthracis definitive identification tests

  • Lysis by specific anthrax g-bacteriophage
  • Detection of capsule by Direct Fluorescent Antibody (DFA) test or microscopy
  • Identification of toxin genes by PCR
• Bacillus anthracis treatment

  Ciprofloxacin or doxycycline combined with one or two additional antibiotics (rifampin, vancomycin, penicillin, imipenem, clindamycin, clarithromycin)
• Bacillus anthracis prophylaxis

  Ciprofloxacin or doxycycline for 4 weeks + three doses of vaccine (or for 8 weeks if no vaccine is administered)
• Bicarbonate-containing medium

  1. 7% CO2
• Bacillus anthracis Laboratory diagnosis - Microscopy


  • Large, gray to white colonies
  • Nonhemolytic
  • Dry, ground glass surface
  • Rough texture (R), irregular edges with projections, comma-shaped outgrowths (Medusa head morphology)
  • Sticky colonies
• Bacillus anthracis Laboratory diagnosis - Culture

  • Lysis by a specific anthrax g-bacteriophage
  • Detection of the capsule by Direct Fluorescent Antibody (DFA) test or microscopy
  • Identification of the toxin genes by PCR
  • Tests usually done in public health laboratories
• Bacillus anthracis Laboratory diagnosis - Definitive identification

  Ciprofloxacin or doxycycline combined with one or two additional antibiotics (rifampin, vancomycin, penicillin, imipenem, clindamycin, clarithromycin)
• Bacillus anthracis Treatment - Other immunotherapies

  • Anthrax immunoglobulin
  • Human monoclonal antibodies with high affinity for PA (e.g., raxibacumab)
  • Available for use in consultation with the CDC
• Bacillus anthracis Prevention and Control

  • Active immunization of domestic animals
  • Burning of died infected animals
  • Decontamination of animal products
  • Protective clothing and gloves for handling potentially infected materials
• Bacillus anthracis Prevention and Control - Human vaccines

  • Limited usefulness
  • FDA approved human vaccine (AVA BioThrax)
  • Provide short-lived immunity
  • New recombinant PA vaccines are being developed
• Bacillus cereus


  • Gram-positive rods
  • Spore-forming
  • Beta-hemolytic on sheep blood agar
• Bacillus cereus Virulence factors - Enterotoxins

  • Heat-stable and heat-labile enterotoxins
  • Necrotic toxin (heat-labile toxin)
  • Cereolysin (hemolysin)
  • Phospholipase C (lecithinase)
• Bacillus cereus Virulence factors - Enterotoxins

  • Heat-stable, proteolysis-resistant enterotoxin: Emetic form of the disease
  • Heat-labile enterotoxin: Diarrheal form of the disease
  • Similar to the enterotoxins produced by Escherichia coli and Vibrio cholerae
  • Stimulates the adenylate cyclase-cAMP system; leads to profuse watery diarrhea
• Bacillus cereus Clinical diseases

  • Food poisoning (Emetic form, Diarrheal form)
  • Ocular infections
  • Other infections (Intravenous catheter infection, Central nervous system shunt infections, Endocarditis, Pneumonitis, bacteremia, and meningitis)
• Bacillus cereus Food poisoning - Emetic form

  • Implicated food: Rice
  • Incubation period: < 6 hours (intoxication)
  • Symptoms: Vomiting, nausea, abdominal cramps
  • Duration: 8-10 hours
  • Enterotoxin: Heat-stable
• Bacillus cereus Food poisoning - Diarrheal form

  • Implicated food: Meat, vegetables
  • Incubation period: > 6 hours (infection)
  • Symptoms: Diarrhea, nausea, abdominal cramps
  • Duration: 20-36 hours
  • Enterotoxin: Heat-labile
• Bacillus cereus Ocular infection


  • Acquired by traumatic, penetrating injuries to the eye with a soil-contaminated object with spores
  • Patient will present with: keratitis, endophthalmitis, panophthalmitis
  • Disseminated infections with ocular manifestations can also develop (intravenous drug abusers)
• Isolation of B. cereus in the stool is not diagnostic: Fecal colonization is common
• Isolation of the organism from the stools of a cluster of epidemiologically related patients is strong evidence implicating B. cereus as the causal agent
• Bacillus cereus Treatment


  • Gastroenteritis: symptomatic treatment
  • Serious non-foodborne infections: Vancomycin, clindamycin, ciprofloxacin, and gentamicin
• Bacillus cereus Prevention


  • Rapid consumption of foods after cooking
  • Proper refrigeration of uneaten foods