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Title: Gram-Positive Bacilli: Spore-formers Chapter 17 Bacillus


1
Gram-Positive Bacilli Spore-formers Chapter 17
  • Bacillus species

2
Bacillus Species General Characteristics
  • Gram-positive spore-formers vs. nonspore-formers

Corynebacterium sp. (no spores)
Bacillus sp. (spore-forming)
3
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
4
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

5
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

6
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

7
Virulence Factors
  • Virulence factors work together to produce
    damage
  • Polypeptide capsule
  • Potent exotoxins

8
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

9
Bacillus anthracis
Clinical Infections in Humans
  • Cutaneous anthrax

10
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

11
Laboratory Diagnosis
  • Goal in identification is to RULE OUT B.
    anthracis
  • If B. anthracis is suspect, MUST work under
    safety hood

12
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)

13
Laboratory Diagnosis Bacillus anthracis
  • B. anthracis in a gram stain from a cutaneous
    lesion

14
Laboratory Diagnosis Bacillus anthracis
  • B. anthracis colonies showing finger-like edges
    and beaten egg whites consistency

15
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

16
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

17
Other Bacillus species
  • Bacillus subtilis
  • Common laboratory contaminant

B. cereus colony on blood agar Large, Ɵ-
hemolytic colony
18
Laboratory Identification Bacillus anthracis
19
  • Aerobic Actinomycetes

20
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

21
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

22
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
23
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.
24
Laboratory Diagnosis Nocardia, Actinomadura, and
Streptomyces species
  • Expectorated sputum with purulence
  • Gram-positive filamentous bacilli
  • Suspicious for actinomycetes

25
Laboratory Diagnosis Nocardia, Actinomadura, and
Streptomyces species
  • Incubation time
  • 3-6 days

26
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.
27
Streptomyces
  • Species
  • Streptomyces somaliensis
  • Streptomyces anulatus
  • Streptomyces paraguayensis
  • Habitat
  • Soil and decaying vegetation
  • Disease states
  • Mycetoma- a chronic, localized, painless,
    subcutaneous infection

28
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

29
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
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