AEROBIC BACILLUS
Lecture (15)
Dr. Baha,H,AL-Amiedi
Ph.D.Microbiology
General Characteristics of Bacillus
60 species; Gram-positive or Gram-variable bacilli
Large (0.5 x 1.2 to 2.5 x 10 um)
Most are saprophytic contaminants or normal flora
Bacillus anthracis
Human pathogen
Isolation also considered to be clinically significant
Zoonosis
Bacillus cereus
Environmental organism
Contaminates food
Common cause of food poisoning
Bacillus stearothermophilus
Tolerates very high temperatures
Used for quality control of autoclaves
Bacillus anthracis
Bacillus anthracis is most important member
Produce endospores
Aerobic or facultatively anaerobic
Catalase positive (most)
Rapidly differentiates from Clostridium
Bacillus spp. are ubiquitous
Soil, water, and airborne Thermophilic (< 75°C) and psychrophilic (>5-8°C)
Can flourish at extremes of acidity & alkalinity (pH 2 to 10)
Transmission:
1-cutaneous anthrax result from contact with spores & contact with infected animals & animals products.
2-inhalation anthrax result when spores inhaled.
3-Gastrointestinal anthrax result when spores are ingested.
Virulence factors
1-A capsule of D-glutamic acid is antiphagocytic and helps the anthracis to evade the immune system of the host.
2-The product of exotoxin
Mode of toxin action
Three exotoxins subunit are product:
1-protctive Antigen(PA):binds to toxin receptor on cell surface of host &facilitates translocation of the two other exotoxins,
2-Edema Factor(EF): is an adenlyate cyclase that increase intracellular cAMP
Stimulating efflux of fluids &ion that result the edema.
3-Lethal Factor(LF):it is a mitogen-activted protein kinase kinase(MAPKK) protease that disrupts signaling causing cell death &tissue necrosis
Pathogenesis and clinical presentations
Cutaneous anthrax
About 20% mortality
Inhalation anthrax
High mortality
Gastrointestinal anthrax
High mortality
Clinical Presentation of Anthrax Cutaneous Anthrax
95% human cases are cutaneous infections
1 to 5 days after contact
Small, pruritic, non-painful papule at inoculation site
Papule develops into hemorrhagic vesicle & ruptures
Slow-healing painless ulcer covered with black eschar surrounded by edema
Infection may spread to lymphatics w/ local adenopathy
Septicemia may develop
20% mortality in untreated cutaneous anthrax
Clinical Presentation of Anthrax Inhalation Anthrax
Virtually 100% fatal (pneumonic)
Meningitis may complicate cutaneous and inhalation forms of disease
Pharyngeal anthrax
Fever
Pharyngitis
Nneck swelling
Clinical Presentation of Anthrax Gastrointestinal (Ingestion) Anthrax
Virtually 100% fatal
Abdominal pain
Hemorrhagic ascites
Paracentesis fluid may reveal gram-positive rods
Epidemiology of Bacillus anthracis
Enzootic in certain foreign countries (e.g., Turkey, Iran, Pakistan,and Sudan)
Anthrax spores infectious for decades
Bacillus cereus
Pre formed Large, motile, saprophytic Heat resistant spores
heat and acid stable toxin (Emetic syndrome)
bacillus
Heat labile enterotoxin (Diarrhoeal disease)
Lab diagnosis – Demonstation of large number of bacilli in food
Laboratory diagnosis:
1-Microscopic Examination
Smear prepared from exudates ,sputum show gram positive bacilli non-bacilli occur in chain
2-Macfadyen test; it is special stain for capsular of bacilli
3-Seriological test (Ascoli test): it is rapid precipitate diagnosis test.
Ascoli test
It is used in making rapid diagnosis,the infected tissues are grounded in saline boiled for 5 minutes & filtered. extracted tissue is layered over anthrax antiserum.
Zone of precipitate at the junction of tissue extract and antiserum within 5 minutes at room temperature means test is positive.
Laboratory Characteristics of Bacillus
4-Cultur ;On blood agar
Large, spreading, gray-white colonies, with irregular margins (Medosa head shape)
Many are beta-hemolytic (helpful in differentiating various Bacillus species from B. anthracis)
Spores seen after several days of incubation in central by smear gram stain examine,
5-Animal inoculation: injected guinea pig subcutaneously which die within 36-48 hours,smear from
Heart blood &spleen show gram positive bacilli.
Treatment
Antibiotic such ciprofloxin ,doxcycline &other are used for treatment