Bacillus, Clostridium, Corynebacterium and Listeria (Gram-Positive)

This entry is on the medically important gram-positive bacteria that are rods. They are categorized as spore-forming (bacillus and clostridium) and non-spore-forming (corynebacterium and listeria).

Bacillus anthracis
The only bacterium with a capsule made of protein called poly-D-glutamic acid. Commonly known as anthrax, which infects cows and sheep and is then transferred to humans by contact. Its spores are very hardy and germinate inside the body, releasing exotoxins. Diseases can be treated with penicillin.

• Diseases:
• Cutaneous anthrax from spore germination on skin wounds. 
• Exotoxin release causes localized tissue necrosis that can progress to skin edema and shock in ~10% of cases. Spore proliferation in the bloodstream can cause death. 
• Pulmonary aka Respiratory anthrax. 
• Macrophages take up spores in the lungs, and transport them to hilar and mediastinal lymph nodes at the bronchi and heart, respectively. There, spores proliferate and cause mediastinal hemorrhage and pleural effusions.
• GI anthrax
• Ingestion of spores cause necrotic lesion in the intestine. Results in vomiting, abdominal pain and bloody diarrhea.
• Exotoxin proteins:
• Edema factor (EF) increases cAMP, which impairs neutrophil function and disrupts water homeostasis (edema).
• Protective antigen (PA) promotes entry of EF into phagocytic cells.
• Lethal factor (LF), enzyme that inactivates protein kinase, and stimulates macrophages to release TNF and IL-1β.

Bacillus cereus
Causes food poisoning due to the bacteria depositing spores and enterotoxin (an exotoxin that targets intestine) into food. Bacteria are not encapsulated, and are resistant to penicillin.

Clostridium botulinum
Produces a lethal neurotoxin that causes rapid and severe food poisoning. The neurotoxin blocks ACh release, leading to muscle paralysis.

• Diseases:
• Adult botulism, with difficulty swallowing (dysphogia), double vision caused by bilateral cerebral nerve palsies, and muscle weakness leading to paralysis and death. Respiratory failure from poor ventilation.
• Infant botulism, with initial constipation then difficulty swallowing and muscle weakness. Prognosis is better than that of an adult.

Clostridium tetani
Commonly found in soil and animal feces, and causes tetanus. Spores deposited in wounds germinate in an anaerobic environment, such as necrotic tissue. The release of exotoxin tetanospasmin, taken up by the neuromuscular junction to the CNS, prevents the release of inhibitory neurotransmitters GABA and glycine. This results in a high frequency of impulses and a sustained contraction. Diseases include respiratory failure, lockjaw and other severe muscle spasms.

Clostridium perfringens
Anaerobic, found in soil, releases exotoxin enzymes and produces gas.

• Diseases:
• Cellulitis/wound infection, where bacterial growth from necrotic skin damages local tissue.
• Clostridial myonecrosis in the muscle, damage by exotoxins and fatal unless treated early. Other enzymes released by the bacteria form gas bubbles within muscle and subcutaneous tissue.

Clostridium difficile
After the use of broad spectrum antibiotics, which can wipe out intestinal flora, the colonization of the C. difficile and the release of its exotoxins cause severe diarrhea, cramps and fever.

Corynebacterium diphtheriae
Colonizes the pharynx, where the bacteria forms a pseudomembrane of fibrin, leukocytes, necrotic epithelial cells and C. diptheriae cells. Exotoxin release at this site into the bloodstream interferes with protein synthesis in the heart and CNS. Causes diphtheria.

Listeria monocytogenes
An exception to the pattern of gram-positive bacteria, L. monocytogenes possesses endotoxin. They can hide within macrophages and neutrophils, and are likely to invade infants and immunosuppressed patients whose immune systems are weak. They are one of the common causes of meningitis.