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BacillusBacillus Aerobic Gram-Positive Bacilli Slide 2 Bacillus Large, G(+) rods, square cut ends Saprophyte in nature; soil, dust Aerobic, facultative anaerobic Spore former, survive in environment Lab presumptive ID by spore stain Most motile B. anthracis = non-motile Slide 3 Bacillus: Genera B. anthracis - charcoal carbuncle; major pathogen, anthrax disease B. cereus waxen, gastroenteritis (rice, meat, vegetable), opportunistic infections B. subtilis isolated as contaminant in clinical specimens, opportunistic infections (catheter, prosthesis) Slide 4 Bacillus: Lab Culture Grows well on ordinary lab media, CBA Large granular colonies, irregular edge; coarse, dull or frosted-glass texture B. cereus = hemolytic B. anthracis = non- hemolytic Slide 5 Bacillus anthracis: Virulence Factors Capsule resist phagocytosis; lab presumptive ID by stain or DFA (direct fluorescent antibody) test Exotoxins complex, coded by plasmid; three genes (three proteins, each alone not toxic) Protective antigen (PA) - bind Lethal factor (LF) - active Edema factor (EF) - active PA combine with LF or EF, binds to host cell receptor, entry into host cell; LF & EF toxic Slide 6 Bacillus anthracis: Two Toxins Lethal toxin: PA + LF; protease, causes cell death Edema toxin: PA + EF; increase in cAMP, results in edema Both toxins: increase vascular permeability interferes with phagocytosis Slide 7 Bacillus anthracis: Anthrax Mainly disease of animals - acquire MO by ingestion or inhalation of spores Spores extremely resistant, source of infection in soil 2-3 years Humans acquire anthrax: Contact animal products (hides, fur, wool, hair) Less commonly, work in agricultural setting with infected animals Disease depends on mode of transmission Skin (cut, abrasion, wound) Ingestion Inhalation Slide 8 Cutaneous Anthrax Most common (95% infections) Spores enter exposed skin, germinate, multiply Exotoxin released, rapid development of pustule Occasionally, MO disseminate - septicemia, death in few days Vascular injury - edema, hemorrhage, thrombosis Death - respiratory failure, anoxia by toxin on CNS Mortality ~20% if untreated Slide 9 Gastrointestinal Anthrax Ingest spores, inoculated into lesions of mucosa Ulcers in mouth, esophagus, intestine GI tract symptoms nausea, vomiting, malaise Lead to lymphadenopathy, edema, sepsis Rapidly progress to systemic disease High mortality, as anthrax not suspected Slide 10 Inhalation Anthrax (Woolsorter s Disease) Inhale spores by aerosols into RT Germinate in lungs, multiply, spread to cause fatal septicemia or meningitis Most serious form of disease High mortality, as anthrax not suspected Use as biologic weapon need to break up spore clumping, aerosolize, so can reach airway CDC category A Select Biological Agent Weaponized spores inhaled, easily disseminated Inhalation anthrax fatal unless treated immediately Slide 11 Bacillus anthracis: Treatment and Prevention Sensitive to penicillin, but some strains now showing resistance Ciprofloxacin drug of choice, Control infection in animals: Vaccine useful to prevent infection Bury diseased animals Short-term PA vaccine available for at high risk individuals, less useful Slide 12 Bacillus cerus: Opportunistic Infections Ubiquitous, infecton via contaminated soil Gastroenteritis two different enterotoxins (emetic, diarrheal) Cytotoxin - cerolysin, phospholipase) Eye infection traumatic injury Endocarditis commonly IV drug abuser Pneumonitis, bacteremia, meningitis - immunocompromised patient, neonate, IV- catheter, surgery patient Resistant to penicillin combination treatment of clindamycin + gentamycin Slide 13 Food Poisoning: Emetic Form Contaminated fried or boiled rice, spores survive cooking Rice not refrigerated, spores germinate, MO release enterotoxin Intoxication ingest toxin in rice; toxin not destroyed by reheating rice Short incubation Food Poisoning: Diarrheal Form Infection ingest contaminated soup, meat, vegetable, sauce, pudding Longer incubation >6 hr., MO multiplies, release toxin; diarrhea, nausea, abdominal pain, vomiting (25%) Last >24 hr. Both forms of food poisoning short, uncomplicated Symptomatic treatment adequate Prevent by proper food handling Slide 15 Class Assignment Textbook Reading: Chapter 16 Aerobic Gram-Positive Bacilli Bacillus Key Terms Learning Assessment Questions Slide 16 Case Study 6 - Bacillus A 56-year-old female postal worker sought medical care for fever, diarrhea, and vomiting. She was offered symptomatic treatment and discharged from the community hospital emergency department. Five days later she returned to the hospital with complaints of chills, dry cough, and pleuritic chest pain. A chest radiograph showed a small right infiltrate and bilateral effusions but no evidence of a widened mediastinum. Slide 17 Case Study 6 - Bacillus She was admitted to the hospital, and the next day her respiratory status and pleural effusions worsened. A computerized tomographic (CT) scan of her chest revealed enlarged mediastinial and cervical lymph nodes. Pleural fluid and blood was collected for culture and was positive within 10 hours for gram-positive rods in long chains. Slide 18 Case Study - Questions 1. The clinical impression is that this woman has inhalation anthrax. What tests should be performed to confirm the identification of the isolate? 2. What are the three primary virulence factors found in B. anthracis? 3. Describe the mechanisms of action of the toxins produced by B. anthracis. 4. Describe the two forms of B. cereus food poisoning. What toxin is responsible for each form? Why is the clinical presentation of these two diseases different?