Chapter 13: Microbe Human Interactions

Normal biota

harmless &beneficial microbes (difficult to remove from skin)

Normal Resident Microbiota

Microbes that engage in mutual or commensal associations with humans

Transient Organisms

found on the skin for short periods of time but DO NOT grow there, could be a pathogen

• easily removed (washing)

• destroyed by the host’s defenses

• cannot compete with the resident normal flora

• may be flushed away by bodily secretions like sweat, oil, and urine

True Pathogen

causes disease in a healthy person

Opportunistic pathogen

causes disease when the host’s defenses are compromised

Example: C. Diff

Pathogenicity

an organism’s potential to cause infection or disease

Epidemiology

Study of the frequency and distribution of disease and other health-related factors in a defined human population

Example would be effects of disease on communitiesD

Direct Contact

transferring microbes from person to person

Indirect Contact

microbes pass from the infected host to the intermediate conveyor (non-living) and then to another host

Fomite

an inanimate object capable of allowing microbe to survive but not reproduce (dry, has no food or water)

Oral - fecal

contamination through contact with fecal matter

A reservoir of infection

any inanimate object that allows a microbe to grow and reproduceA

Airborne Transmission

respiratory secretions & air itself

• Droplet Nuclei - microscopic mucus & saliva create dried pellets in the air

• Aerosols - fine dust or moist particles that contain live pathogens, like dust from soil and animal quarters

Chain of Infection

1. Portal of Entry - characteristic route a microbe follows to enter the tissues of the body

   1. Exogenous agent - originates from a source outside the body

   2. Endogenous agent - already exists on or in the body (normal flora); they typically enter through the respiratory tract or the digestive system

2. Attaching to the host

   1. Adhesion - when a microbe establishes a stable association with the host’s cells

3. invading & becoming established - microbes have mechanisms for disabling and evading a host’s defenses

   1. Toxins - can damage target cells

   2. Inhibition - microbe capsules

   3. Destruction - destruction of WBC

4. Causes of damage & disease - pathogens weaken host tissues

   1. Necrosis - tissue death

   2. Direct damage to cells through toxins or enzymes

5. Portals of Exit - pathogens depart by a specific avenue, which greatly influences the dissemination of infection

   1. respiratory & salivary portals - mucus, nasal drainage, Etc.

   2. Epithelial cells - skin & scalp

   3. Fecal exit

   4. Urogenital tract

   5. Removal of blood or bleeding

Stages of Clinical Infection: Incubation period

time from initial contact to appearance of the first symptom

Stages of Clinical Infection: Prodromal stage

short period (2 days), earliest notable symptoms, small discomfort

Stages of Clinical Infection: Period of invasion

infective agent multiples at its highest levels

Stages of Clinical Infection: Convalescent Period

Recovery symptoms decline, gradually return to normal

Carrier

An individual who inconspicuously shelters a pathogen & spread it to others

Asymptomatic Carrier

shows no symptoms

• Incubation carrier - spreads with infection

• Convalescent carrier - recuperating without symptoms

• Chronic carrier - an individual who shelters the infection for a long period of time

Passive Carrier

Contaminated healthcare provider transfers them to other patients