Bacillus B. anthracis: anthrax of the animals and humans. B. cereus: food poisoning; opportunistic infections. Aerobic or facultatively anaerobic. Large gram-positive rods, have square ends, arranged in long chains. Spore is located in the center of the cell. Most are saprophytic (soil, water, air, and on vegetation.) Morphology and Physiology

B. anthracis B. anthracis is encapsulated and non-motile. The capsule consists of polypeptide (poly-D-glutamic acid). The spores can withstand dry heat and certain disinfectants for moderate periods, and persist for years in dry earth. Animal products contaminated with anthrax spores can be sterilized only by autoclaving. Physiology and Structure

B. anthracis Primarily a disease of herbivores (sheep, cattle, horses); humans are rarely affected. Being used by the terrorists as a biological warfare. In animals, portal of entry is mouth and GI tract. In humans, scratches in the skin (95% of infection), ingestion or inhalation lead to infection. Inhalation is the most likely route for infection with biological weapons (LD 50 : 2,500-55,000). The spores germinate in the tissue at the site of entry, and growth of the vegetative forms results in gelatinous edema and congestion. Bacillus spread via lymphatics to the blood and other tissues. Pathogenesis and Immunity

Spores in the soil Spores from Germination of the carcasses  spores in the soil Grazing animals infected through injured mucous membrane Infection in humans

B. anthracis Virulence factors Capsule (encoded from a plasmid) Exotoxins (A-B toxins encoded from another plasmid) Edema toxin is composed of protective antigen (B- subunit) and edema factor (has adenylate cyclase activity). This toxin complex increases vascular permeability which leads to shock. Lethal toxin is composed of protective antigen and lethal factor (a metalloprotease). This toxin stimulates macrophages to release proinflammatory cytokines. Pathogenesis and Immunity

B. anthracis Cutaneous anthrax (malignant pustule): develops in hours. The papule rapidly changes into a vesicle, then a pustule, and finally a necrotic eschar. The infection may disseminate, giving rise to septicemia.necrotic eschar Inhalation anthrax (wool-sorters’ disease): long incubation time (2 months or more). Mediastinitis (enlargement of mediastinal lymph nodes), sepsis, and meningitis (50% patients). Pulmonary disease rarely develops. Gastrointestinal anthrax (very rare): symptoms vary depending on the sites of infection. Can result in ulcers in the mouth and esophagus, or abdominal pain, vomiting and bloody diarrhea. May develop into septicemia rapidly with a mortality that can be 100%. Clinical Diseases

B. anthracis Specimens: fluid or pus from local lesion, blood, or sputum. Smears: serpentine chains (a characteristic of B. anthracis) of large gram-positive rods without spores. Immunofluorescence stain for dried smears. Culture: produces nonhemolytic gray colonies with sticky consistency on blood agar plates. Identification: non-motility; gelatin stab: inverted fir tree; or selected biochemical tests. Serological tests: detection of antibodies to lethal toxin and edema toxin. Laboratory Diagnosis

B. anthracis Penicillin is the drug of choice. Resistant to sulfonamides and cephalosporins. Treatment Control Proper disposal of animal carcasses (burning or deep burial in lime pit). Autoclaving of animal products. Protective clothing and gloves for handling infected animals. Vaccination of domestic animals. Immunization of persons at high risk with a cell-free vaccine.

B. cereus and other bacillus species Ubiquitous organisms; primarily opportunistic pathogens. B. cereus: the most important among them. Noncapsulated and motile, causing gastroenteritis gastroenteritis : emetic form and diarrheal form. ocular infections : acute panophthalmitis occurs after traumatic, penetrating injuries of the eye with a soil- contaminated object. intravenous catheter-related sepsis. Other infections: endocarditis, pneumonitis, sepsis, meningitis, etc. Symptomatic treatment is adequate for B. cereus gastroenteritis. The treatment of other Bacillus is complicated because the course is rapid and progressive and they are resistant to multiple drugs. Food poisoning can be prevented by quick consumption and proper storage of food.

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