Chapter 11- Interactions Between Microbes and Humans

human microbiome

All microbes found on and in a normal human; vital to health and physiology.

resident microbiota

Long-term colonizers that typically do not cause disease.

infection

Microbes bypass defenses, enter tissues, and multiply.

disease

Health deviation due to infection damaging tissues/organs.

infectious disease

Disease caused directly by microbes or their products.

microbial antagonism

Competition between microbes that prevents displacement of normal biota.

symbiosis

Relationship where at least one organism depends on the other; applies to host-microbiota.

pathogen

Microbe that causes infection and disease via parasitism.

pathogenicity

Microbe’s potential to cause disease.

true pathogen

Causes disease in healthy individuals.

opportunistic pathogen

Causes disease when defenses are compromised or in unnatural body sites.

virulence

Severity of disease caused; degree of pathogenicity.

virulence factor

Microbial trait that helps establish infection and cause damage.

portal of entry

Site or method of microbe entry into the body.

exogenous infection

Originates from outside the body.

endogenous infection

Originates from within the host.

infectious dose (ID)

Minimum number of microbes needed to cause infection.

adhesion

Microbial attachment to host tissues via specific molecules.

Adhesion (ligand)

Pathogen molecule that binds to host receptors.

receptor

Host molecule that binds microbial adhesins.

phagocyte

Immune cell that engulfs and destroys pathogens.

leukocidin

Toxin that kills phagocytes.

capsule/slime layer

Structures that inhibit phagocytosis.

antiphagocytic factor

Trait that helps microbes evade phagocytosis.

exoenzyme

Secreted enzyme that damages host tissues and promotes spread.

toxin

Poisonous microbial product that harms host cells.

exotoxin

Secreted protein toxin; specific and potent in small amounts.

endotoxin

Lipid toxin (LPS) from gram-negative bacteria; causes systemic effects when released.

portal of exit

Route by which pathogens leave the host to infect others.

local infection

Confined to a small area.

systemic infection

Spread throughout the body.

focal infection

Starts locally, then becomes systemic.

primary infection

Initial acute infection.

secondary infection

Follows primary infection due to weakened defenses.

acute disease

Rapid onset, short duration.

chronic disease

Slow development, long duration.

asymptomatic infection

Active infection without noticeable symptoms.

symptom

Subjective change felt by the patient (e.g., fatigue, nausea).

sign

Objective, measurable change (e.g., fever, vomiting).

syndrome

Group of signs/symptoms that define a disease.

incubation period

Time between pathogen contact and symptom onset.

prodromal stage

Early vague symptoms (e.g., malaise, aches).

acute phase

Peak infection; high microbial activity and symptoms.

convalescent period

Recovery phase; symptoms decline, health returns.

continuation phase

Symptoms persist or pathogen lingers after recovery.

reservoir

Natural habitat where a pathogen originates.

transmitter

Source from which infection is acquired.

carrier

Infected individual who spreads disease without symptoms.

zoonois

Animal-origin infection transmissible to humans.

fomite

Nonliving object that transmits pathogens.

vehicle

Nonliving medium (air, water, soil, food) that transmits pathogens.

vector

Living organism (often arthropod) that transmits pathogens.

communicable disease

Spread from one host to another.

contagious disease

Easily and rapidly spread between hosts.

noncommunicable disease

Not spread between hosts.

horizontal transmission

Spread between individuals in a population.

vertical transmission

Passed from parent to offspring (e.g., placenta, milk).

direct contact

Transmission via close physical interaction.

indirect contact

Transmission via objects or substances.

vector transmission

Transmission via arthropods or other organisms.

Healthcare-associated infection (HAI) (nosocomial infection)

Infection acquired during medical treatment.

compromised host

Individual with weakened defenses due to illness or procedures.

biofilm

Microbial community on surfaces (e.g., catheters); promotes infection.

infection control committee

Group overseeing infection prevention in large facilities.

infection control officer

Individual responsible for infection control in smaller facilities.

epidemiology

Study of disease frequency and distribution in populations.

etiologic agent

Cause of infection and disease.

case reporting

Legal requirement to report notifiable diseases.

incidence

Number of new cases in a time period; measures risk.

prevalence

Total number of cases (new + existing); measures disease burden.

mortality rate

Number of deaths due to a disease.

morbidity rate

Number of people afflicted with a disease.