Lect 17 Pathogens

Human microbiome

The collection of all the microorganisms living in association with the human body

Pathogens

Organisms that can infect humans and cause illness in a strategy for their own survival

Opportunistic Pathogens

cause disease by taking advantage of a host's increased susceptibility to infection

Obligate ("Primary") Pathogens

Can cause disease regardless of individual's health

Pathogenicity

The structural and biochemical mechanisms whereby microorganisms cause disease

A pathogen must be able to:

- Adhere to, penetrate, and persist in the host

- Avoid, evade, or compromise host defenses

- Damage the host and permit spread of infection

- Exit from host and infect another

Invasiveness

ability to spread to adjacent tissues

Invasiveness encompasses

Mechanisms for colonization, Production of extracellular substances, Ability to bypass or overcome host defense mechanisms

Portals of Entry

Any point at which organisms can enter body; Primary requirement for infection

Portals of Entry Categories

Mucous membranes, Skin, Parenteral routes

Virulence

Degree of fitness of the pathogen to overcome the body's defenses and establish themselves

Toxigenesis

Ability to produce and actively secrete substances that either

damage host tissues or protect the bacteria against host defenses

Infection

Invasion of the body by pathogens that reproduce and multiply, causing disease and local cell injury, toxin secretion, or antigen-

antibody reaction

Colonization

The presence of a pathogen (disease-causing microbe) that is not currently associated with a systemic serological immune

antibody response

Bacterial Adherence to Mucosal Surfaces

receptors and ligand (adhesin)

Tissue tropism

Particular bacteria are known to have an apparent preference for certain tissues over others

Viruses

They possess genes, evolve by natural selection, and reproduce themselves with help; They don't have their own metabolism, and they don't have a cellular structure

Mechanism of viral entry

enter cells and damage them by replicating at the expense of the host; can only replicate inside the (living) cells

This tropism is influenced by 3 primary things:

Host receptors for the virus, Specificity of transcription factors in the viral DNA. Physical characteristics of tissue encountered by the virus

Host receptors for virus

virus's protein coat allows for binding, sometimes need proteases

Specificity of transcription factors in viral DNA

recognition of viral enhancer and promoter elements

Physical characteristics of tissue encountered by virus

environment, temperature, pH, etc.

Mechanisms of cell injury/death

Direct cytopathic effects; Anti-viral immune responses; Transformation of infected cells into growing and surviving new type of cells

Direct cytopathic effects

Preventing the cell from making the things it needs- HSV inhibit cellular DNA and mRNA, degrading host DNA

Viral Infection length

3-21 days

Incubation

1-7 days after exposure, replication occurring

Prodrome

initial symptoms for 1-3 days

Illness

less intense symptoms for 5-14 days

Viral shedding

highly concentrated in secretions of lungs/mucosa, variable time

Covid-19

an enveloped positive-stranded RNA virus

The host receptor for cell entry is

angiotensin-converting

enzyme 2 (ACE2) receptor

covid-19 transmission

Direct person-to-person respiratory droplet transmission