4/30/2025 Notes | BIOL 412

HUMAN MICROBIOME CONTINUED

  • strain level variation

  • dietary influence

    • Western diet affects ratio between Bacteroides and Prevotella

  • functional stability

    • redundancy in function, so some species are interchangeable

Topic: Infection

SUMMARY

  • different stages of infection

  • bacterial virulence factors

  • role of virulence factors in the context of stages of invasion

DEFINITIONS

  • reservoir: environment where the pathogen naturally reproduces and from which susceptible hosts can be infected

  • pathogen: an opportunistic/obligate organism that lives on a host and produces disease; an extension of predation

    • agent of pathogenicity

  • host: the organism that is affected by the pathogen, deriving a negative effect

  • disease: tissue damage or injury caused by a pathogen that impairs host function

  • infection: growth of microorganisms that are not normally present within a host

  • pathogenicity: ability to cause disease (qualitative)

    • lists traits

  • virulence: relative ability of a pathogen to cause disease (quantitative)

STEPS OF INFECTION AND DISEASE

  • the infection process

    • exposure —> adherence —> invasion —> multiplication

  • the disease process

    • toxicity/invasiveness —> tissue or systematic damage

  • adherence by…

    • capsule

    • pili

    • fimbriae

  • invasion: entrance into host cells or tissues with the intent to spread and cause disease

    • access to cells or intracellular space (pathogen-dependent)

  • multiplication: growth of pathogen and cell division

    • growth and production of virulence factors and toxins

  • infection does not imply damage

  • disease can lead to systemic damage, where the entire host organisms is affected

  • molecular structures of adhesion

    • adhesins: glycoproteins or lipoproteins found on the pathogen’s surface that enable it to bind to host cells

  • portal of entry: route of access to host tissues by the pathogen (as way of initial entry)

  • mucous membranes: host’s epithelial cells that secrete mucus, thick proteins, and glycoprotein solutions

  • endotoxins: toxins released by the pathogen upon cell death

    • ex. Salmonella, E. coli

  • exotoxins: toxins released by the pathogen as it grows

    • ex. cytolytic toxins, haemolytic toxins, AB toxins, superantigens

VIRULENCE AND VIRULENCE FACTORS

  • virulence: the net outcome of host pathogen interactions

    • can be measured as relative to other pathogens or non-pathogenic taxa

    • quantitation: the number of cells that induce pathogenic effect on a host

      • can be due to toxicity and/or invasiveness

  • LD50: lethal dose of the substance sufficient to kill 50% of test animals