Distinguish among four types of symbiosis
- Mutualism
- Commensalism
- Amensalism
- Parasitism
Mutualism
Organism 1: Benefits
Organism 2: Benefits
Example: Bacteria in human colon
Commensalism
Organism 1: Benefits
Organism 2: Neither benefits nor is harmed
Example: Mites in human folicles
Amensalism
Organism 1: Neither benefits nor is harmed
Organism 2: Is harmed
Example: Fungus secreting an antibiotic inhibiting nearby bactera
Parasitism
Organism 1: Benefits
Organism 2: Is harmed
Example: Tuberculosis bacteria in human lung
Microbiome
- Organisms that colonize the body’s surfaces without normally causing disease
- Also known as normal flora and indigenous microbiota
Resident microbiota
- Are part of the normal flora throughout life
- Are mostly commensal
Transient microbiota
- Remain in the body for short period of time
- Found in the same regions as resident microbiota
- Cannot persist in the body:
- Competition from other microorganisms
Three conditions that create opportunities for normal microbiota to cause disease are
- Introduction of normal microbiota into an unusual site in the body; changes in the relative abundance of normal microbiota
- Immune suppression
- Stressful conditions
Three types of reservoirs of infection in humans
- Animal reservoir
- Human carriers
- Nonliving reservoir
Define contamination
The mere presence of microbes in or on the body
Define infection
When an organism evades body’s external defenses, multiplies, and becomes established in the body
What are three major portals of entry in which pathogens invade the body?
- Skin
- Mucous membranes
- Placenta
Portals of Entry: Skin
- Outer layer of dead skin cells acts as a barrier to pathogens
- Some pathogens can enter through opening or cuts
- Others enter by burrowing into or digesting outer layers of skin
Portals of Entry: Mucous Membranes
- Line the body cavities that are open to the environment
- Provide a moist, warm environment hospitable to pathogens
- Respiratory tract is the most common site of entry, other entry include nose, mouth, or eyes
- Gastrointestinal tract may be route of entry but the bacteria must survive the acidic pH of the stomach
Portals of Entry: Placenta
- Placenta typically forms effective barrier to pathogens
- Pathogens may cross the placenta and infect the fetus which can cause spontaneous abortion, birth defects, and premature birth
Compare and contrast the terms infection, disease, morbidity, pathogenicity, and
virulence.
- Infection is the invasion
- Disease, also known as morbidity is if the invading pathogen alters the normal body function
- Pathogenicity is the ability of the microorganism to cause disease
- Virulence is the degree of pathogenicity
Define infection
Infection is the invasion of the host by a pathogen
Define disease
- Disease results if the invading pathogen alters normal body function
- Also referred to as morbidity
Define pathogenicity
Pathogenicity is the ability of a microorganism to cause disease
Define virulence
Pathogenicity is the ability of a microorganism to cause disease. Virulence is the degree of pathogenicity. Virulence factors that contribute to virulence include:
- Adhesion factors
- Biofilms
- Extracellular enzymes
- Toxins
- Antiphagocytic factors
Define etiology
- Study of the cause of disease
- Diseases have various causes
Define symptoms
- Subjective characteristics of disease felt only by the patient
Define signs
- Objective manifestations of disease observed or measured by others
