3.1 Relationship between Microbes and Humans Study Guide

Mutualism

A type of symbiotic relationship in which both organisms benefit.

Commensalism

A relationship where one organism benefits while the other is neither helped nor harmed.

Parasitism

A relationship in which one organism (the parasite) benefits at the expense of the other (the host).

Synergism

A relationship where both organisms work together to achieve a result that neither could accomplish alone.

Antagonism

A relationship in which one organism inhibits or interferes with the growth of another.

Antibiosis

A type of antagonism where one organism produces substances that kill or inhibit another organism.

Methanobrevibacter smithii example

Commensalism.

Pathogenicity

Ability of an organism to cause disease.

Virulence

The degree or severity of disease a pathogen can cause.

Virulence factors

Adhesins; capsules; toxins; exoenzymes; antigenic variation.

Infection tasks

Enter → adhere → evade → obtain nutrients → multiply & spread.

Portal of entry

The route or site through which a pathogen enters the host.

Exogenous vs Endogenous

Exogenous = external source; Endogenous = from within the host.

More infectious → lower infectious dose?

True.

Adherence structures

Fimbriae/pili; adhesive capsules; surface proteins.

Adhesins

Molecules on adherence structures that bind to host cell receptors.

Avoid phagocytosis

Capsules; inhibit phagosome-lysosome fusion; kill/escape phagocytes.

Hemolysin is an endotoxin?

False (it’s an exotoxin).

Gram-negative → endotoxin

True (endotoxin is part of LPS).

Exoenzymes

Enzymes secreted to break down host tissues (e.g. hyaluronidase

Superantigens

Toxins that overstimulate immune system by activating many T-cells.

Infection stages

Incubation; Prodromal; Acute; Decline; Convalescent.

Incubation phase

Pathogen multiplies with no signs or symptoms yet.

Most severe stage

Acute.

First signs/symptoms stage

Prodromal.

Stopping antibiotics prematurely

Decline phase (symptoms improve but pathogens remain).

Nausea

Symptom.

Back pain

Symptom.

Low blood pressure

Sign.

Blurred vision

Symptom.

Swelling

Sign.

Reservoir

Habitat where a pathogen normally lives (humans

Environmental reservoir possible?

True.

Direct vs Indirect contact

Direct = physical contact; Indirect = via object (fomite).

Droplet vs Airborne

Droplet = larger particles

Vector vs Vehicle

Vector = living transmitter (e.g. mosquito); Vehicle = inanimate transporter (e.g. food

Sneezing → doorknob → another

Vehicle-borne.

Vertical transmission

Parent → offspring (pregnancy

Horizontal transmission

Spread among same generation (e.g. person to person).

Susceptibility factors

Age; immune status; nutrition.

Contagious disease

Easily transmitted from one person to another.

Not all infectious are contagious

True (e.g. tetanus).

HAI sites

Urinary tract; respiratory tract; bloodstream; surgical sites; skin.

High-risk age group for HAIs

Infants and elderly.

Common HAI bacteria

Staphylococcus aureus (MRSA); Escherichia coli; Klebsiella pneumoniae; Pseudomonas aeruginosa.

Asymptomatic carrier

Carries & transmits pathogen but shows no signs or symptoms.

Reportable vs Notifiable disease

Reportable = must be reported to authorities; Notifiable = diseases of public health concern tracked by authorities.

Pandemic

A global disease outbreak.

Epidemic

Sudden increase in cases in a region.

Endemic

Disease constantly present in a region.

Sign

Objective—can be seen or measured by others (e.g., rash, fever, high blood pressure).

Symptom

Subjective—what the patient feels or reports (e.g., pain, nausea, fatigue).