MEDI 3104 Bacterial Pathogenesis

Bacterial Pathogenesis and Virulence

• Commensals vs. Pathogens: Commensals are harmless microbes (normal flora) that coexist with the host, while pathogens are capable of causing disease.
• Infection vs. Colonization: Infection occurs when a microbe grows in/on the body, potentially causing disease. Colonization is when bacteria multiply without invading tissues.
• Pathogenicity vs. Virulence: Pathogenicity is the ability to cause disease; virulence is a measure of pathogenicity, reflecting the severity of the disease produced.
• Opportunistic Pathogens: Cause disease primarily in immunocompromised individuals, such as those with HIV or undergoing chemotherapy.
• Nosocomial Infections: These are infections acquired in a hospital setting, while iatrogenic infections are caused by medical treatment.

Stages of Bacterial Pathogenesis

• Transmission: The initial stage involves the entry of bacteria into the host.
• Adherence: Bacteria adhere to cell surfaces using structures like pili and adhesins.
• Invasion and Survival: This includes tissue invasion, triggering inflammation, and surviving intracellularly.
• Toxin Production: Pathogens produce toxins that can damage host cells and tissues.
• Evasion of Immune System: Pathogens employ strategies to avoid detection and destruction by the host's immune system.

Modes of Transmission

• Ingestion: Example pathogens include Salmonella and Shigella, which can cause severe gastrointestinal issues.
• Inhalation: Airborne pathogens such as Mycobacterium tuberculosis and Streptococcus pneumoniae are significant causes of respiratory tract infections.
• Direct Contact: Transmissions can occur through unclean hands or breaks in the skin, with Staphylococcus aureus and Pseudomonas aeruginosa being common culprits.
• Sexual Transmission: Pathogens like Neisseria gonorrhoeae and Treponema pallidum are transmitted through sexual contact.
• Blood Borne Transmission: Pathogens like HIV can be transmitted through needlestick injuries and unsterile practices.
• Vector Borne: Insects like mosquitoes can spread diseases such as malaria; mechanical vectors include flies transmitting bacteria like Salmonella.
• Vertical Transmission: Involves transmission from mother to fetus (TORCH infections include Toxoplasma and Rubella).

Infective Dose

• Low Infective Dose: Shigella requires as few as 10 organisms to cause disease.
• High Infective Dose: Vibrio cholerae needs an estimated 10^6 to 10^8 organisms for infection.

Colonization Factors

• Adherence Mechanisms: Bacteria attach to host tissues via pili, which bind to specific receptors.
• Adhesins: Proteins like M protein in Streptococcus pyogenes aid in the adherence process.

Toxin Production

• Exotoxins vs. Endotoxins:
  • Exotoxins are proteins released by bacteria and can provoke strong immune responses; they can be vaccine candidates (e.g., toxoids).
  • Endotoxins, particularly lipopolysaccharides (LPS) from the Gram-negative bacteria cell wall, induce general immune responses, such as fever.

Genotypic Virulence Factors

• Plasmids: Circular DNA molecules that can confer traits like antibiotic resistance or toxin production.
• Bacteriophage: Viruses that infect bacteria, influencing bacterial characteristics and virulence.
• Transposons: Segments of DNA that move within the genome, altering bacterial properties and enhancing virulence.

Additional Factors in Pathogenesis

• Leukocidins: Substances produced by some bacteria (e.g., PVL by MRSA) that can kill immune cells like neutrophils and macrophages, enhancing bacterial survival.

Explore the intricacies of bacterial pathogenesis and virulence in this MEDI 3104 quiz. Delve into the differences between commensal organisms and pathogenic bacteria along with their modes of action. Enhance your understanding of microbiology and immunology concepts essential for medical studies.