Properties

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment & Prevention

Bacillus anthracis

Large Gram positive rods.

Spores visible within bacterium

Grow well on blood agar aerobically.

Nonmotile.

Transmission:

- spores widespread in soil for years.

- humans are infected by spores on animal products such as hides, bristles, & wool.

- contact with sick animals.

- portal of entry: mucous membranes, respiratory tracts.

Virulence factor: antiphagocytic capsule.

Anthrax toxin:

- protective antigen.

- lethal factor.

- edema factor

Cutaneous anthrax:

- typical lesion is a painless ulcer with a black necrotic eschar.

- surrounded by a ring of vesicles & an area of edema.

- untreated cases progress to bacteriamia & death.

Respiratory anthrax:

- due to inhalation of spores.

- severe pneumonia with haemorrhage.

- leads to septicaemia & death.

Smears show large, gram positive rods in chains.

Colonies form on blood agar aerobically.

No serologic tests are useful.

Penicillin.

Prevention:

- sterilize dead animals & animal protects.

- persons at risk immunized with cell-free vaccine purified protective antigen.

Bacillus cerus

Transmission:

- spores on rice survive heating & rapid frying, germinate when rice is kept warm.

- portal of entry is gastrointestinal tract.

Produces two enterotoxins.

Two forms of food poisoning:

- rapid onset (4 hrs): nausea & vomiting.

- slow onset (18 hrs): diarrhea & abdominal pain.

Occasional causes of wound infection & invasive infection in immunocompromised patients.

Grow bacteria from food or stool though this is usually not done.

Store cooked food in refrigerator, stir fry thoroughly.