Introduction to Microbiology - Lecture 19

Introduction to Microbiology - Lecture 19

• Gram-positive bacteria, under harsh environment conditions (nutrient depletion), undergo sporulation.
• Sporulation involves creating new structures, enzymes and metabolites while breaking down vegetative cell components.
• Spores contain a complete copy of the chromosome, essential proteins and ribosomes, and a high calcium-dipicolinic acid concentration.

Endospores

• Spores are highly resistant to desiccation, heat, and chemical agents allowing them to survive for centuries in a viable state.
• When returned to favourable conditions, spores germinate into a single vegetative cell.
• Spore location within the cell can help in identifying the bacterium.
• Spore structure and formation processes vary between different species.

Bacillus species

• Bacillus species are large aerobic, gram-positive rods often forming chains.
• Important pathogens within this group include Bacillus anthracis and Bacillus cereus.

Clostridium species

• Clostridium species are gram-positive rods, obligate anaerobes.
• Important pathogens within this group include Clostridium difficile, Clostridium perfringens, Clostridium tetani, Clostridium botulinum.

Bacillus anthracis

• Found as large, gram-positive rods or long chains.
• Spores not typically seen in clinical samples.
• Disease is primarily a concern for herbivores.
• Humans can be infected through contact with animals or products containing the organism.
• Infection routes include inoculation, ingestion, and inhalation.
• Main factors contributing to the virulence are the capsule, edema toxin, and lethal toxin.
• The capsule made of poly-d-glutamic acid inhibits phagocytosis of replicating cells.
• Edema toxin is responsible for fluid accumulation in anthrax.
• Lethal toxin is cytotoxic and stimulates macrophages to release proinflammatory cytokines.
• Sporulation and the development of vegetative organisms result in gelatinous edema and congestion.
• Recovery is rare without immediate treatment in many cases.

Bacillus cereus

• Bacillus cereus is a ubiquitous organism present in various environments.
• Causes two types of food poisoning: vomiting (emetic) and diarrheal disease.
• Emetic form results from consumption of contaminated rice containing enterotoxin, not the bacteria itself.
• The incubation time in this case is short (1 to 6 hours).
• Diarrheal form is a true infection, resulting from ingesting contaminated meat, vegetables, or sauces.
• A longer incubation period is associated with this type of infection.
• Bacillus cereus can also cause ocular infections, usually after eye injuries with soil-contaminated objects.
• Spores retain the dye used in the staining process.

Clostridium difficile

• Disease develops in individuals taking antibiotics, altering the normal enteric flora and making them susceptible to Clostridium difficile.
• Fecal transplants have shown remarkable success in treating Clostridium difficile, demonstrating its dependence on gut bacteria for survival.
• Pseudomembranous colitis is the inflammatory condition of the colon usually occurring in C difficile cases.

Clostridium perfringens

• Clostridium perfringens is a large rectangular gram-positive rod, with spores.
• Colonies are often distinguished by rapid spreading growth.
• Commonly inhabits the intestinal tracts of humans and animals.

Clostridium perfringens - Food poisoning

• Is a food poisoning characterized by a short incubation period (8–12 hours), clinical manifestations including abdominal cramps, and lasts less than 24 hours.
• The enterotoxin is produced during the phase transition from vegetative cells to spores. This toxin is released in the alkaline environment of the small intestine during sporulation.

Clostridium perfringens - Soft tissue Infections

• Clostridium perfringens is responsible for various soft tissue infections, including cellulitis, fasciitis, suppurative myositis, and myonecrosis (gas gangrene).
• The causative toxin is known as alpha-toxin.

Clostridium tetani

• Clostridium tetani is a large, motile, spore-forming rod.
• Often found in fertile soil. It can transiently inhabit the GI tract of animals as well as humans.
• There are two kinds of toxins, oxygen labile hemolysin (tetanolysin) and heat labile neurotoxin (tetanospasmin).
• Tetanospasmin inactivates proteins involved in neurotransmitter glycine and GABA release in the spinal cord and brainstem, leading to unregulated excitatory synaptic function and spastic paralysis.
• Disease is relatively uncommon due to the high incidence of vaccine immunity.

Clostridium botulinum

• Clostridium botulinum is a heterogeneous collection of large, fastidious, spore-forming, anaerobic rods commonly isolated from soil and water.
• It is associated with foodborne botulism. Foodborne botulism is typically associated with consuming home-canned foods, leading to symptoms that appear 1-3 days after consuming the food. This includes descending weakness of peripheral muscles and eventually respiratory failure.

Infant botulism

• Infant botulism is associated with consuming foods like honey, infant milk powder, contaminated with botulinum spores leading to ingestion of these contaminants.
• The contamination of soil and dust containing these spores can cause neurotoxin production directly in the infant's GI tract.

Botulism - Clinical presentation

• The botulinum neurotoxin remains at the neuromuscular junction.
• This toxin inactivates proteins responsible for acetylcholine release.
• The net result is a flaccid paralysis.

Explore the fascinating processes of sporulation in gram-positive bacteria, including their survival mechanisms under harsh environmental conditions. This lecture emphasizes the structure, formation, and significance of endospores, particularly in Bacillus species. Discover the role of spores in bacterial identification and their resistance to extreme conditions.