Anthrax, Bacillus Cereus, and Listeria: Characteristics, Pathogenesis, and Prevention
Bacillus anthracis:
Bacillus anthracis can enter through the skin, gastrointestinal tract, and the airway (less frequent but more lethal).
- Gram-positive bacilli
- Facultative anaerobe
- Forms spores that can survive for years
- Undemanding growth
- Presents a polypeptide capsule (poly-D-glutamic acid)
- Coded by 3 genes: capB, capC (Plasmid 1)
- Plasmid 2 (B. anthracis virulence)
Encodes 3 Exotoxins:
- Protective antigen (binds to the host cell)
- Edema factor
- Lethal factor
Edema Toxin:
Edema factor + protective antigen = responsible for severe edema, a protective feature of infection.
Lethal Toxin:
Protective antigen + lethal factor.
Avirulent Strains:
Removing one or both plasmids can result in avirulent strains (harmless). Plasmid 1 encodes the capsule, and plasmid 2 encodes exotoxins.
Pathogenesis and Immunity:
Capsule inhibits phagocytosis. Edema toxin is an adenylate cyclase. Lethal toxin is a zinc metalloprotease, stimulating macrophages to release TNF-alpha and interleukin.
Routes of Infection in Humans:
Inoculation, ingestion, inhalation.
3 Cycles of B. Anthracis in Nature:
Multiplication of spores in the soil, food infection, human infection.
Types of Anthrax:
Cutaneous anthrax: Inoculation, 1-12 days, with itching and clear exudate.
Gastrointestinal anthrax: Inoculation, 1-7 days, with nonspecific symptoms (fever, nausea, abdominal pain).
Inhalation anthrax: Latency period of 2 months, asymptomatic (more lethal).
First Phase:
Nonspecific symptoms: fever, shortness of breath, cough, headache, vomiting, chills, abdominal pain, and chest pain.
Second Phase:
Worsening of symptoms, edema, significant mediastinal lymphadenopathy accompanied by symptoms of meningitis, shock, and death.
Prevention:
Vaccination of animals and people at risk (cattle workers). Infections must be incinerated to prevent sporulation.
Bacillus cereus:
- Opportunistic pathogen
- Low virulence
- Gram-positive spore-forming
- Facultative anaerobe
- Undemanding growth
Risk Groups:
- Consumption of contaminated food (rice, meat, vegetables, sauces)
- Penetrating injuries in the eye
- Intravenous injections
- Hemolysin: RBC destruction
- Lethal factor: Death occurs in animals.
- Vascular permeability factor: Causes changes in blood vessels.
- Necrotic toxin: Necrosis of the bowel.
Food Poisoning:
- Emetic form: Consumption of rice contaminated with heat-resistant spores, incubation time 1-6 hours.
- Diarrheal form: Consumption of contaminated meat, vegetables, or sauces.
LISTERIA
(Easy contamination of refrigerated food).
- Disease in humans: Listeria monocytogenes
- Small, gram-positive bacilli
- Facultative anaerobe
- Isolated, in pairs, or short chains
- Mobile at room temperature
- Stationary at 37°C
Risk Groups:
Neonates, elderly, pregnant women, immunocompromised individuals.
- Introduced into the cell via internalins, interacting with surface glycoprotein receptors on the host cell.
- Habitat: Ground, water, vegetation, intestinal contents of mammals, birds, and fish. 1-5% in healthy human carriers.