Bacterial Polymers and Biofilms Quiz

Mechanisms of Bacterial Virulence

• A pathogen is an organism that causes disease in a host.
• Pathogenicity is the ability to initiate an infectious disease.
• Virulence is the capacity to cause disease and the severity of the disease.
• Transmissibility is the ability to spread from human to human or reservoir to human.
• Survival is the ability to avoid destruction by the host's immune system, reproduce, and obtain nutrients within the host.
• Infectivity is the capacity to overcome host defenses.
• Virulence factors are the proteins or molecules produced by an organism to promote its pathogenicity.

Virulence Factors Classification

• Cytosolic factors: Changes in metabolic rate, physiological functions, and morphological structures.
• Membrane-associated factors: Aid in adhesion to host tissues and cells, and in evading host immunity.
• Secretory factors: Used to enter tissues and evade innate and adaptive immune responses.

Steps to Bacterial Infection

• Transmission: Exposure to pathogens.
• Adherence: Binding to the skin or mucosa.
• Invasion: Breaking through barriers.
• Survival: Growth at original and distal sites, producing virulence factors.
• Tissue damage: Toxicity and disease.

Transmission Reservoirs

• Human reservoirs: Person-to-person transmission (asymptomatic carriage).
  • Examples: COVID, HIV, Measles, Mumps, Streptococcal infection, Respiratory pathogens.
• Animal reservoirs: Animal-to-animal or animal-to-human transmission.
  • Examples: Brucellosis (cows and pigs), Anthrax (sheep), Plague (rodents), Trichinellosis (swine), Rabies (bats, dogs).
• Environmental reservoirs: Plants, soil, and water.
  • Examples: Cholera outbreaks (Vibrio Cholera in contaminated water), Legionnaires' disease (caused by water in cooling towers).

Transmission Mechanisms

• Direct contact: Direct body surface contact (skin-to-skin contact, sexual transmission, mother-to-neonate).
  • Examples: HIV, Staphylococcal infections, infectious mononucleosis, Gonorrhoea.
• Indirect contact: Contact via contaminated objects (fomites).
  • Examples: Cholera, Salmonella, Listeriosis, Viral hepatitis.
• Droplets: Generated via coughing, sneezing, and talking; carrying microorganisms.
  • Examples: Influenza, Pneumonia, Meningococcal infections, Pertussis, Anthrax spores, Tuberculosis, SARS-CoV-2, Varicella, Hantaviruses.
• Zoonoses: Animal-to-human transmission.
  • Animal bites (Rabies, Hepatitis), Animal products (contaminated meat, animal hides), Invertebrate vector-borne (ticks, mosquitos, fleas) (Lyme's disease, Malaria, Yellow fever, Typhus, Plague).

Portal of Entry and Exit

• Various routes through which bacteria enter (Mucous membranes (epithelium), Skin damage, Vertical transmission (across placenta, through the gametes), Specialized entry).
• The various routes through which bacteria exit the body(Respiratory tract, Gastrointestinal tract, Genitourinary tract, Skin, blood).
• Environmental adaptation for pathogen transmission.
• Key pathogens require adaptation to survive in differing environmental conditions (Temperature, pH, Oxygen levels, Host cell immune response, Nutrient availability).

How Pathogens Achieve Colonization

• Cell surface components: Adhesion, defense against immunity (e.g., pili, fimbriae, flagella, EPS, CPS (capsule)).
• Active combat: Invasive enzymes (e.g., coagulase, kinases, hyaluronidase, collagenase), Nutrient acquisition, Toxins.
• General strategies: Dealing with phagocytosis, Communication/Intelligence signals, Subverting apoptosis.
• Adhesion: The process of bacteria attaching to tissues or cells, crucial for colonization
• Adhesion factors: Proteins such as pili, fimbriae and flagella enable attachment. Specialized surface structures (EPS, CPS)
• Structural components of bacteria: Can act as toxins eg. LPS

Active Combat

• Invasive enzymes: Coagulase, Kinases, Hyaluronidase, Collagenase, IgA proteases.
• Toxins: Botulinum, Shiga toxin, Staphylococcal enterotoxin, differing LD50 values. Different toxin groups, and structures.
• LPS (Lipopolysaccharide): Gram-negative bacteria's outer membrane component, triggering Toll-like receptor 4 (TLR4), leading to an inflammatory response and fever. Little inherent toxicity.
• Exotoxins: Specific toxins damaging or manipulating the host. (Single polypeptide toxins, Multiple polypeptide toxin complexes, Small "drug-like" molecules, Toxins directly injected).

Active Combat - Specialized Toxin Delivery Systems

• Secretory systems in bacteria to deliver virulence factors to host cells.
• Type I, II, V, III, IV, VI, VII secretory systems in Gram-positive and Gram-negative bacteria.
• Specialized mechanisms for injecting toxins into host cells. (e.g. Toxin complex, Injector, Toxin adaptor, toxin).

Biofilms

• After initial attachment, bacteria form biofilms for enhanced survival.
• Biofilms are colonies adhering to each other and forming on abiotic surfaces and host tissues.
• Biofilms provide a barrier against host defenses, antibiotics, and immune factors.
• Complex architecture allowing for nutrient flow and waste removal