Chapter 14: Objectives

Question 1

Distinguish among four types of symbiosis

Answer 1

• Mutualism
• Commensalism
• Amensalism
• Parasitism

Question 2

Mutualism

Answer 2

Organism 1: Benefits
Organism 2: Benefits
Example: Bacteria in human colon

Question 3

Commensalism

Answer 3

Organism 1: Benefits
Organism 2: Neither benefits nor is harmed
Example: Mites in human folicles

Question 4

Amensalism

Answer 4

Organism 1: Neither benefits nor is harmed
Organism 2: Is harmed
Example: Fungus secreting an antibiotic inhibiting nearby bactera

Question 5

Parasitism

Answer 5

Organism 1: Benefits
Organism 2: Is harmed
Example: Tuberculosis bacteria in human lung

Question 6

Microbiome

Answer 6

• Organisms that colonize the body’s surfaces without normally causing disease
• Also known as normal flora and indigenous microbiota

Question 7

Resident microbiota

Answer 7

• Are part of the normal flora throughout life
• Are mostly commensal

Question 8

Transient microbiota

Answer 8

• 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

Question 9

Three conditions that create opportunities for normal microbiota to cause disease are

Answer 9

• Introduction of normal microbiota into an unusual site in the body; changes in the relative abundance of normal microbiota
• Immune suppression
• Stressful conditions

Question 10

Three types of reservoirs of infection in humans

Answer 10

• Animal reservoir
• Human carriers
• Nonliving reservoir

Question 11

Define contamination

Answer 11

The mere presence of microbes in or on the body

Question 12

Define infection

Answer 12

When an organism evades body’s external defenses, multiplies, and becomes established in the body

Question 13

What are three major portals of entry in which pathogens invade the body?

Answer 13

• Skin
• Mucous membranes
• Placenta

Question 14

Portals of Entry: Skin

Answer 14

• 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

Question 15

Portals of Entry: Mucous Membranes

Answer 15

• 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

Question 16

Portals of Entry: Placenta

Answer 16

• 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

Question 17

Compare and contrast the terms infection, disease, morbidity, pathogenicity, and
virulence.

Answer 17

• 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

Question 18

Define infection

Answer 18

Infection is the invasion of the host by a pathogen

Question 19

Define disease

Answer 19

• Disease results if the invading pathogen alters normal body function
• Also referred to as morbidity

Question 20

Define pathogenicity

Answer 20

Pathogenicity is the ability of a microorganism to cause disease

Question 21

Define virulence

Answer 21

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

Question 22

Define etiology

Answer 22

• Study of the cause of disease
• Diseases have various causes

Question 23

Define symptoms

Answer 23

• Subjective characteristics of disease felt only by the patient

Question 24

Define signs

Answer 24

• Objective manifestations of disease observed or measured by others

Question 25

Define syndrome

Answer 25

Symptoms and signs that characterize a disease or abnormal condition

Question 26

Define asymptomatic

Answer 26

• Also known as subclinical, infections that lack symptoms but may still have signs of infection

Question 27

Explain how microbial extracellular enzymes, toxins, adhesion factors, and
antiphagocytic factors affect virulence

Question 28

How microbial extracellular enzymes affect virulence

Answer 28

• Extracellular enzymes are secreted by the pathogen
• Dissolve structural chemicals in the body
• Help pathogen maintain infection, invade, and avoid the body’s defenses
• Important: Mutant species that do not secrete the enzymes are often avirulent

Question 29

How toxins affect virulence

Answer 29

• Toxins are chemicals that harm tissues or trigger host immune responses that cause damage
• Toxemia refers to the presence of toxins in the bloodstream; carried beyond the site of infection
  Two types:
• Exotoxins
• Endotoxins

Question 30

How antiphagocytic factors affect virulence

Answer 30

• Prevent phagocytosis by the host’s phagocytic cells
• Allow pathogens to remain in a host for a longer time

Question 31

Define epidemiology

Answer 31

• Epidemiology is the study of where and when diseases occur and how they are transmitted within population; frequency of disease
• Keep track of the occurrence of diseases by using two measures:
• Incidence: Number of new cases
• Prevalence: number of total cases