Chapter 15: Microbial Mechanisms of Pathogenicity

Pathogenicity

Ability of a microorganism to cause disease.

Virulence

Degree of pathogenicity; measures how severe a disease is.

Portal of Entry

Pathogen entry point into the body.

Common Portals of Entry

Mucous membranes, skin, parenteral route.

Mucous Membranes

Entry via respiratory, digestive, or genitourinary tracts.

Skin as a Portal of Entry

Usually blocks pathogens; entry through hair follicles and sweat glands.

Parenteral Route

Direct deposition beneath skin or mucous membrane.

Infectious Dose (ID₅₀)

Infectious dose for 50% of hosts.

Lethal Dose (LD₅₀)

Lethal dose for 50% of hosts.

Lower ID₅₀

Indicates greater infectious potential.

Lower LD₅₀

Indicates greater lethality.

Adhesins

Surface proteins used by pathogens to attach.

Host Receptors

Mannose-containing glycoproteins that facilitate attachment.

Capsules

Structures that prevent phagocytosis.

Function of M Protein

Prevents phagocytosis in Streptococcus pyogenes.

Coagulase

Enzyme that creates fibrin clots around bacteria.

Kinases

Enzymes that destroy blood clots to allow bacterial spread.

Hyaluronidase

Enzyme that breaks down hyaluronic acid to aid bacterial mobility.

Collagenase

Enzyme that breaks down collagen to invade connective tissues.

IgA Proteases

Enzymes that destroy IgA antibodies to avoid immune defenses.

Siderophores

Molecules that steal iron from the host.

Antigenic Variation

Change in surface antigens to evade immune recognition.

Invasins

Molecules that alter host cytoskeleton for bacterial entry.

Biofilms

Communities of microbes embedded in extracellular polymeric substance (EPS).

Exotoxins

Toxins secreted by bacteria, often proteins.

Endotoxins

Components of the bacterial cell wall, such as Lipid A of LPS.

A-B Toxins

Toxins with an active component (A) and a binding component (B).

Shiga Toxin

Inhibits protein synthesis in host cells, originating from certain bacteria.

Hemolysins

Toxins that destroy red blood cells.

Leukocidins

Toxins that destroy white blood cells.

Superantigens

Stimulate massive immune response, causing cytokine release.

Plasmids

Genetic elements that may carry virulence factors such as toxins.

Viral Pathogenicity

Mechanisms viruses use to evade the immune system.

Fungal Pathogenicity

Disease caused by toxins, proteases, and allergic reactions.

Protozoan Pathogenicity

Disease caused by tissue damage, waste products, and antigenic variation.

Helminth Pathogenicity

Disease caused by tissue damage, immune reactions, and nutrient theft.

Tetanus Case

Caused by tetanus toxin from Clostridium tetani, not contagious.

Food Infection

Microbe grows inside the body, usually causing fever and diarrhea.

Food Intoxication

Preformed toxin consumed, leading to neurological symptoms.

Capsules and Virulence

Capsules prevent phagocytosis, increasing virulence.

Importance of Mannose Receptors

Common attachment sites for pathogenic E. coli.

Shiga Toxin Effect

Inhibits protein synthesis in cells leading to cell death.

Exotoxins vs. Endotoxins

Exotoxins are proteins; endotoxins are primarily Lipid A.

ID₅₀ and Infectivity

Lower ID₅₀ indicates greater infectivity.

LD₅₀ and Virulence

Lower LD₅₀ indicates greater virulence.

Blood as Portal of Entry

Blood is NOT a portal of entry for pathogens.

Tetanus Symptoms

Caused by tetanus toxin, indicating intoxication not infection.

Function of Siderophores

Allow bacteria to obtain iron from the host, crucial for growth.

Biofilms and Antibiotics

Biofilms protect microbes from antibiotics and immune responses.