Bacillus and Clostridium

• Bacillus and Clostridium cause diseases through potent exotoxin release, differing biochemically in their oxygen preference.
• Bacillus thrives with oxygen (aerobic), whereas Clostridium multiply in anaerobic conditions.

Bacillus Overview

• Two pathogenic, gram-positive, aerobic, spore-forming Bacillus species exist: Bacillus anthracis and Bacillus cereus.
• Bacillus anthracis causes anthrax, while Bacillus cereus causes gastroenteritis (food poisoning).

Bacillus anthracis (Anthrax)

• Bacillus anthracis spores remain dormant in the soil and are heat, drying, UV light, and disinfectant resistant.
• Spores germinate in the lungs, intestines, or skin wounds, producing toxins, with virulence factors regulated by temperature (37°C), carbon dioxide concentration, and serum proteins.
• Spores are phagocytosed by macrophages and become vegetative gram-positive rods.
• Bacteria reproduce in the lymphatic system then invade the bloodstream.
• It's unique due to its protein-based capsule (poly-D glutamic acid that prevents phagocytosis.
• Due to small size (1-2 μm), stability, and mortality associated with inhalation pulmonary anthrax, the spores could be used for biological terrorism and warfare.

Cutaneous Anthrax

• Bacillus anthracis multiplies rapidly, releasing a potent exotoxin that causes localized tissue necrosis resulting in painless, round black skin lesions with edema.
• Untreated, it can disseminate causing death.

Gastrointestinal Anthrax

• Results in death after spore ingestion (contaminated meat).
• Bacillus anthracis replicates in the intestine and releases exotoxin, causing necrotic lesions
• Symptoms include vomiting, abdominal pain, and bloody diarrhea.

Anthrax Toxins

• Toxins are encoded on plasmid pXO1
• A second plasmid, pXO2, encodes genes for the poly-glutamyl capsule synthesis.
• Exotoxin contains three separate proteins to produce the systemic effects
• Edema factor (EF) increases cAMP, impairs neutrophil function, and causes massive edema. It is the active A subunit which is is a calmodulin-dependent adenylate cyclase.
• Protective antigen (PA) promotes entry of EF into phagocytic cells, that is similar to the B subunit of A-B toxins
• Lethal factor (LF) inactivates protein kinase, is a zinc metalloprotease. This stimulates macrophages to release tumor necrosis factor-alpha and interleukin-1/3.
• Critical to use ciprofloxacin or doxycycline for prevention in systemic infections.

Bacillus cereus

• Motile, non-encapsulated, and penicillin-resistant.
• It causes food poisoning (nausea, vomiting, and diarrhea) when spores in food survive cooking and then germinate and release enterotoxin.
• Exposure to high temperatures and/or refrigeration inactivates the spores.
• Secretes 2 enterotoxins to cause food poisoning:
• Heat labile toxin similar to cholera and E. coli LT toxin causing nausea, abdominal pain, and diarrhea, lasting 12-24 hours.
• A Heat-stable toxin produces a clinical syndrome similar to Staphylococcus aureus food poisoning, with a short incubation period followed by severe nausea, vomiting, with limited diarrhea.

Clostridium Overview

• Includes anaerobic, gram-positive, spore-forming rods
• Causes botulism, tetanus, gas gangrene, and pseudomembranous colitis.
• Clostridium spores float in the air and can land on food.
• If the food is cooked thoroughly, the spores will die.
• If the spores are not cooked sufficiently, and are then placed into an anaerobic environment (like a glass jar, can, or zip-lock freezer bag), Clostridium botulinum matures and synthesizes its neurotoxin.

Clostridium botulinum (Botulism)

• Produces a neurotoxin that blocks acetylcholine release causing flaccid muscle paralysis.
• Eating smoked fish or home-canned vegetables is transmission of botulism.
• Afebrile patients develop bilateral cranial nerve palsies (double vision and difficulty swallowing), followed by muscle weakness, respiratory paralysis, and death.
• Treatment involves immediate antitoxin administration and ventilatory support.

Wound Botulism

• It is the least common presentation of botulism.
• Wound Botulism is associated with puncture wounds or deep space Infections.
• Provides environment for spores from the soil or environment to germinate and produce toxin.
• Symptoms are similar to adult botulism except for absence of gastrointestinal symptoms and a longer Incubation period.
• More likely to have a fever and an associated elevation of their white count.
• Treatment consists of surgical debridement of devitalized tissue, anti-toxin, and usually antibiotics to cover Clostridia and other co-existent pathogens.

Infant Botulism

• Occurs when infants ingest food contaminated with Clostridium botulinum spores (fresh honey).
• Spores germinate, colonize the infant's intestinal tract, and release toxin.
• Causes constipation initially, followed by difficulty swallowing and muscle weakness.
• Requires hospitalization and supportive therapy.

Clostridium tetani (Tetanus)

• From Clostridium tetani spores are found in soil and animal feces and can germinate in necrotic tissue.
• Exotoxin called tetanospasmin release from the bacteria cells, results in a sustained contraction of skeletal muscles called tetany
• From the neuromuscular junction (end plate) tetanus toxin is transported to the central nervous system.
• Tetanus toxin acts on inhibitory Renshaw cell interneurons, preventing the release of GABA and glycine neurotransmitters.
• Results in high-frequency impulses to muscle cells, causing sustained tetanic contraction.
• Presents with severe muscle spasms, especially in the jaw (trismus, or lockjaw), grotesque grinning expression (risus sardonicus)
• Mortality is high once lockjaw stage is reached.
• Tetanic contraction of the respiratory muscles also results in respiratory failure.
• Protection lasts about 10 years. Booster shots of tetanus are given every 10 years
• Botulism causes flaccid muscle paralysis by blocking acetylcholine, while tetanus causes constant muscle contraction by blocking inhibitory signals.

Clostridium perfringens (Gas Gangrene)

• Clostridium perfringens matures in anaerobic conditions and produces gas.
• Spores contaminate wounds (battle wounds) or other trauma.
• Spores also germinate in foods like meats, poultry, and gravy, leading to toxin production and watery diarrhea if large amounts are ingested.
• A severe diarrheal illness can lead to hemorrhagic necrosis of the jejunum.

Clostridium perfringens - Types

• Cellulitis/wound infection exposes necrotic skin to Clostridium perfringens that then grows and damages local tissue.
• Palpation reveals a moist, spongy, crackling consistency to the skin (Crepitus) due to gas pockets.
• Clostridial myonecrosis occurs when Clostridium perfringens secretes exotoxins destroying muscle. These bacteria ferment carbohydrates, resulting in gas formation.

Clostridium difficile (Pseudomembranous Enterocolitis)

• C. difficile spores can be found in the environment: Broad-spectrum antibiotics can wipe out normal intestinal flora, allowing C. difficile to super infect the colon
• C. difficile grows in abundance, it then releases its exotoxin causing psuedomembranous enterocolitis
• Toxin A causes diarrhea and Toxin B is cytotoxic to the colonic cells.
• Characterized by severe diarrhea, abdominal cramping, and fever.
• A potent newer strain, NAP1/BI/027, produces much more toxin and a new binary toxin, CDT, and is associated with outbreaks.

Clostridium difficile - Diagnosis & Treatment

• PCR testing for toxin A and B genes is the preferred test due to its excellent sensitivity, specificity, and quick turn-around time.
• Enzyme immunoassay (EIA) for toxins A and B is commonly done but only 75% sensitive.
• Treatments include discontinuing initial antibiotic therapy and beginning appropriate therapy.
• Metronidazole is recommended for mild cases or vancomycin for severe disease or relapse.
• Metronidazole and Vancomycin antibiotics can effectively kill C. difficile. Vancomycin is not absorbed when taken orally and therefore remains in the gastrointestinal tract at the site of infection
• Fidaxomicin, approved in 2011, is superior to vancomycin to treat recurrences.
• Fecal transplantation is effective at preventing recurrent disease in persons who have had multiple relapses of C. difficile.

Questions cover differentiating characteristics between Bacillus cereus and Bacillus anthracis, Bacillus cereus's mechanisms of food poisoning, and effective inactivation methods. Also covers Clostridium botulinum and infant botulism.