AAB Gram positive cocci questions and answers

Bacillus anthracis Disease Anthrax. Primarily disease of herbivores/ruminants- cows. Cutaneous anthrax most common; GI and inhalation possible but not common. Those have 100% fatality. Bacillus anthracis Characteristics Aerobic, gram-positive, spore-forming rods. Capsule composed of poly-D-glutamate. B. anthracis is the only medically important organism that has a capsule composed of amino acids rather than polysaccharides. Bacillus anthracis Habitat and Transmission Habitat is soil. Transmission is by contact with spores from infected animals (cows). Woolsorters' Disease. Bacillus anthracis Pathogenesis Anthrax toxin consists of three proteins: edema factor, which is an adenylate cyclase; lethal factor, which kills cells by inhibiting a signal transduction protein involved in cell division; and protective antigen, which mediates the entry of the other two components into the cell. The capsule is antiphagocytic. Bacillus anthracis Laboratory Diagnosis Gram-stained smear plus aerobic culture on blood agar. B. anthracis is nonmotile, in contrast to other Bacillus species. Rise in antibody titer in indirect hemagglutination test is diagnostic. Bacillus anthracis Prevention Vaccine consisting of protective antigen is given to individuals in high-risk occupations. Vaccinate animals. Bacillus cereus Disease Food poisoning- toxin. Ocular infection after trauma- cereolysin and phospholipase. Catheter-related sepsis. Bacillus cereus Characteristics Aerobic, gram-positive, spore-forming rod. Bacillus cereus Habitat and Transmission Ubiquitous soil organisms. Habitat is grains, such as rice. Spores survive boiling during preparation of rice, then germinate when rice is held at warm temperature. Bacillus cereus Pathogenesis Two enterotoxins= two forms of disease: (1) diarrheal- formed in vivo. Profuse diarrhea and pain; 10-12 hr incubation; contaminated meat/veggies. (2) Emetic- preformed. Projectile vomiting; contaminated fried rice Bacillus cereus Laboratory Diagnosis Not done. Bacillus cereus Treatment Symptomatic only. Bacillus cereus Prevention No vaccine. Clostridium tetani Disease Tetanus. Clostridium tetani Characteristics Anaerobic, gram-positive, spore-forming rods. Spore is at one end ("terminal spore") so organism looks like a tennis racket. Clostridium tetani Habitat and Transmission Habitat is the soil. Organism enters through traumatic breaks in the skin. Clostridium tetani Pathogenesis Spores germinate under anaerobic conditions in the wound. Organism produces exotoxin, which blocks release of inhibitory neurotransmitters (glycine and GABA) from spinal neurons. Excitatory neurons are unopposed, and extreme muscle spasm (tetanus, spastic paralysis) results. "Lock-jaw" and "risus sardonicus" are two examples of the muscle spasms. Tetanus toxin (tetanospasmin) is a protease that cleaves proteins involved in the release of neurotransmitters. Clostridium tetani Laboratory Diagnosis Primarily a clinical diagnosis. Organism is rarely isolated. Serologic tests not useful. Clostridium tetani Treatment Hyperimmune human globulin to neutralize toxin. Also penicillin G and spasmolytic drugs (e.g., Valium). No significant resistance to penicillin. Clostridium tetani Prevention Toxoid vaccine (toxoid is formaldehyde-treated toxin). Usually given to children in combination with diphtheria toxoid and acellular pertussis vaccine (DTaP). If patient is injured and has not been immunized, give hyperimmune globulin plus toxoid (passive-active immunization). Debride wound. Givetetanus toxoid booster every 10 years. Clostridium botulinum Disease Botulism. Clostridium botulinum Characteristics Anaerobic, gram-positive, spore-forming rods. Clostridium botulinum Habitat and Transmission Habitat is the soil. Organism and botulinum toxin transmitted in improperly preserved food. Clostridium botulinum Pathogenesis Botulinum toxin is a protease that cleaves proteins involved in the release of acetylcholine at the myoneural junction, causing flaccid paralysis. Failure to sterilize food during preservation allows spores to survive. Spores germinate in anaerobic environment and produce toxin. The toxin is heat-labile; therefore, foods eaten without proper cooking are usually implicated. Clostridium botulinum Laboratory Diagnosis Presence of toxin in patient's serum or stool or in food. Detection of toxin involves either antitoxin in serologic tests or production of the disease in mice. Serologic tests for antibody in the patient are not useful. Clostridium botulinum Treatment Antitoxin to types A, B, and E made in horses. Respiratory support may be required. Clostridium botulinum Prevention Observing proper food preservation techniques, cooking all home-canned food, and discarding bulging cans. Clostridium perfringens Diseases Gas gangrene (myonecrosis) and food poisoning. Clostridium perfringens Characteristics Anaerobic, gram-positive, spore-forming rods. Clostridium perfringens Habitat and Transmission Habitat is soil and human colon. Myonecrosis results from contamination of wound with soil or feces. Food poisoning is transmitted by ingestion of contaminated food. Clostridium perfringens Pathogenesis Gas gangrene in wounds is caused by germination of spores under anaerobic conditions and the production of several cytotoxic factors, especially alpha toxin, a lecithinase that cleaves cell membranes. Gas in tissue (CO2 and H2) is produced by o