Bacillus - General Characterstics

General Characteristics of Bacillus anthracis

· Important pathogen in man and domestic animals for thousands of years
· May have been the 5th plague inflicted on the Egyptians during their negotiations with Moses
· Koch's postulates were developed as a result of his studies on this organism
Capsule
- Composed of poly-(D-glutamic acid), single antigenic type- Nontoxic, serves as an impedin in establishment of infection
- Production enhanced in the presence of Na+-bicarbonate- Capsule gene is plasmid-borne

Spores

- Important in natural history- Form in well aerated cultures (32-35oC), inhibited by high [CO2] (dead carcasses), rare in blood and internal organs- Vegetative phase killed by heat (30 min, 60oC), quickly destroyed in decaying carcasses by enzymatic action and effects of putrefactive bacteria
Colony Characteristics

- Aging colonies: ground glass appearance

Anthrax

· Infects humans and domestic animals
· Usually through contact - Contaminated animal tissue - Wool or hair
· Highly fatal: CFR varies with type of illness

Cutaneous Anthrax

· Spores deposited in abrasion, insect bite
· Germinate, vegetative cells multiply and produce toxin
· Vesicle appears, contains serous fluid which later becomes hemorrhagic and blue-black
· Ruptures, leaving round sharp-edged ulcer with hemorrhagic necrotic tissue
· Ulcer dries, its edges separate from surrounding skin, sloughs off
· Lesion develops fully, results in ulceration, even with appropriate therapy, started early
· 5-20% of untreated patients develop septicemia and generalized infection

Inhalation Anthrax (Woolsorter's Disease)

· Dust particles contaminated with spores are inhaled, deposit in terminal alveoli
· Spores engulfed by macrophages, transported to regional LN
· Germinate, vegetative cells produce toxin
· Extensive necrotic hemorrhage, rapid death frequently results
· Multiple organs involved, CFR about 85% even with Rx

Gastrointestinal Anthrax

· Results from ingestion of contaminated meat
· Organisms or spores penetrate oropharynx/intestinal mucosa
· Deposited in submucosal tissue, multiply and produce toxin
· Usually extends to regional LN, systemic symptoms develop
· CFR about 50%

Anthrax in Domestic Animals

· Major naturally-occurring anthrax areas are tropical, subtropical - India, Pakistan - Africa, South America
· Distribution depends upon conditions allowing sporulation in carcass discharges, vegetative multiplication in soil
· Regions with alkaline soils, high nitrogen level (decaying vegetation) - Alternating periods of rain and drought - Temperatures in excess of 15oC: vegetative multiplication - Resporulation upon drying

Disease in Ruminants

· Sedalia Cattle Trail in Oklahoma, first seeded from dying cattle in the 1800's
· Disease is similar in most ruminants
· Typical presentation is septicemia
· Symptoms: - Sudden onset - High fever, bleeding from body openings - Edema - Peracute death in 1-2h, acute in <24 h
Why is it illegal in some countries to perform post-mortem on antrhax-suspects?
· Diagnosis confirmed by clinical signs, strain/culture from peripheral blood
· Carcasses incinerated on site, buried in quicklime well below ground level

Horses

Symptoms: colic, edematous swellings of the throat, neck, shoulders

Swine, Dogs

Symptoms: pharyngeal swelling, gastroenteritis
· Infection by ingestion of contaminated feed - Raw meat from animals dead of anthrax - Infected meat/bone meal
· Enters from upper part of digestive tract (tonsils)
· Disease manifests as inflamatory edema, tissues of head and neck
· Often become distorted swollen
· Suffocation may follow edema of glottis (tongue)


Virulence Factors and Pathogenesis of Anthrax

"Point of no return:"12 hr antemortem - Guinea pigs inoculated intradermally - Antibody/streptomycin administered before 3 x 108 CFU/ml: course of disease reversed, guinea pigs survived - Rx administered after 3 x 108: death ensued, in spite of substantial reduction in number of bacteria
Findings imply involvement of toxin
Sterile blood from dying guinea pig caused same fatal syndrome in normal guinea pig
Fractionation of plasma revealed three factors:
- I (Edema Factor)
- II (Protective Antigen)
- III (Lethal Factor)

Regulation of EF Activity
EF enzyme activity is calmodulin dependent
No calmodulin in procaryotes
No adenylate cyclase activity in other species of Bacillus