Gram-Positive Bacilli: Spore-formers Chapter 17 Bacillus

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Gram-Positive Bacilli Spore-formers Chapter 17

• Bacillus species

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Bacillus Species General Characteristics

• Gram-positive spore-formers vs. nonspore-formers

Corynebacterium sp. (no spores)
Bacillus sp. (spore-forming)
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Bacillus species General Characteristics

• Found in nature, from the arctic to the desert
• Aerobic
• Most are saprophytic and are isolated as
  contaminants
• Bacillus anthracis is a major pathogen
• Others are opportunists

Bacillus sp. stained with spore stain
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Gram-Positive Bacilli Spore-formers

• Spores are produced when the bacteria get
  stressed (i.e. drying, temp.)
• Heat shock (heat to 56o) will induce spore
  formation
• On gram stain, appear as clear areas within the
  bacterial cell
• Spores aid in the survival of the bacteria

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Significant Bacillus Species

• Bacillus anthracis
• Agent of anthrax, a disease in livestock
• Humans acquire infection by contamination of
  wound or ingestion or inhalation of spores
• Bacillus cereus
• Causes food poisoning, frequently from left-over
  rice
• An opportunist
• Bacillus subtilis
• Common laboratory contaminant

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Bacillus anthracis General Characteristics

• Morphology (might resemble Clostridium, except
  for being aerobic and catalase )
• Large, sporeforming gram-positive to
  gram-variable bacilli
• Spores viable for up to 50 years
• Nonhemolytic on sheep blood agar (this
  characteristic differentiates B. anthracis from
  other Bacillus spp.)
• Catalase
• Some strains produce pink to blue-black pigment

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Virulence Factors

• Virulence factors work together to produce
  damage
• Polypeptide capsule
• Potent exotoxins

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Bacillus anthracis
Clinical Infections in Humans

• Cutaneous anthrax or "malignant pustule (also
  called black escher)
• Organisms gain access through cuts localized
  infection
• Majority of cases in the world are cutaneous
• Pulmonary anthrax or "woolsorter's disease
• Acquired through inhalation of spores may result
  in respiratory distress and death
• Gastrointestinal
• Acquired by ingestion of contaminated raw meat
• Usually fatal

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Bacillus anthracis
Clinical Infections in Humans

• Cutaneous anthrax

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Anthrax Complications and Treatment

• Fatality rate of gastrointestinal form is highest
  although rare
• Meningitis may occur in 5 of cases
• Antibiotic therapy penicillin in high doses or
  ciprofloxacin (cipro)
• Vaccination is available to those with high risk
  of exposure

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Laboratory Diagnosis

• Goal in identification is to RULE OUT B.
  anthracis
• If B. anthracis is suspect, MUST work under
  safety hood

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Laboratory Diagnosis Bacillus anthracis

• Microscopic morphology
• Gram stain large, square-ended
  gram-positive/gram- variable rods may appear
  end-to-end giving a "bamboo appearance

• Colonial morphology
• Nonhemolytic on 5 blood agar raised, large,
  grayish-white, irregular, fingerlike edges
  described as Medusa head or beaten egg whites
  (colony stands upright when lifted with loop)

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Laboratory Diagnosis Bacillus anthracis

• B. anthracis in a gram stain from a cutaneous
  lesion

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Laboratory Diagnosis Bacillus anthracis

• B. anthracis colonies showing finger-like edges
  and beaten egg whites consistency

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Other Bacillus species B. cereus

• Food poisoning (can be cultured from stool or
  vomitus)
• Diarrheal syndrome
• Associated with meat, poultry, and soups
• Incubation period of 8 to16 hours
• Fever uncommon
• Resolves within 24 hours
• Emetic form
• Associated with fried rice
• Abdominal cramps and vomiting
• Incubation period of 1 to 5 hours
• Resolves in 9 hours

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Other Bacillus species B. cereus

• Other than B. anthracis, all Bacillus spp. are
  HEMOLYTIC on blood agar
• All Bacillus spp. produce spores and are aerobic
• Infections in the immunosuppressed hosts
• Opportunistic infections of the eye
• Meningitis, septicemia, and osteomyelitis
• Found as contaminants in drug paraphernalia

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Other Bacillus species

• Bacillus subtilis
• Common laboratory contaminant

B. cereus colony on blood agar Large, ß-
hemolytic colony
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Laboratory Identification Bacillus anthracis
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• Aerobic Actinomycetes

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Aerobic ActinomycetesNocardia species

• General Characteristics
• Aerobic, gram-positive, filamentous rods,
  sometimes resembling branched hyphae
• Weakly acid-fast and may stain gram-variable
• Morphologically resemble fungi, both in culture
  and in types of infections produced, but is a
  true bacteria
• Generally found in the environment (primarily
  soil) and mostly affect immunocompromised
  individuals

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Aerobic Actinomycetes Nocardia, Actinomadura,
and Streptomyces species

• Significant Nocardia species (majority isolated
  from sputum and wounds)
• N. asteroides
• N. braziliensis
• N. caviae
• Actinomadura species
• A. madurae
• A. pelletieri
• Streptomyces species

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Aerobic Actinomycetes Nocardia, Actinomadura,
and Streptomyces species

• Clinical infections
• Pulmonary form
• Mostly in immunocompromised
• High fatality
• Starts as lung lesion
• Mycetomas
• Cutaneous
• Invasive
• Gram stain can show sulfur granules (masses of
  organisms may be yellow or orange)

Sulfur granules collected from draining sinus
tracts in mycetoma
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Laboratory Diagnosis Nocardia, Actinomadura, and
Streptomyces species

• Microscopy
• Gram-positive branching filaments are seen in
  direct smears from sputum or aspirated material
• May show beading appearance
• Verify with acid fast stain

Gram-stained smear of sputum showing
Gram-positive branched beaded bacilli.
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Laboratory Diagnosis Nocardia, Actinomadura, and
Streptomyces species

• Expectorated sputum with purulence
• Gram-positive filamentous bacilli
• Suspicious for actinomycetes

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Laboratory Diagnosis Nocardia, Actinomadura, and
Streptomyces species

• Incubation time
• 3-6 days

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Laboratory Diagnosis Nocardia, Actinomadura, and
Streptomyces Species

• Cultural characteristics
• Chalky, matte, dry, crumbly appearance
• May be pigmented
• Identification
• Utilization of carbohydrates
• Hydrolysis of casein, tyrosine, and xanthine

Chalky, white colonies on blood agar plate
isolated from sputum sample consistent with
Nocardia sp. or Streptomyces sp.
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Streptomyces

• Species
• Streptomyces somaliensis
• Streptomyces anulatus
• Streptomyces paraguayensis
• Habitat
• Soil and decaying vegetation
• Disease states
• Mycetoma- a chronic, localized, painless,
  subcutaneous infection

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Streptomyces

• Morphology Characteristics
• Aerobic growth in 3-30 days
• Waxy, bumpy or velvety rugose forms, yellow to
  orange
• Will grown on SBA, mycology media and LJ media
• GPR with extensive branching, chains and spores
• Identification
• Acid-fast negative

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Laboratory Diagnosis Nocardia, Actinomadura, and
Streptomyces Species

• Sputum smear, partially acid-fast bacilli,
  consistent with Nocardia sp.
• Actinomadura and Streptomyces sp. are not
  acid-fast