Microbe-Host Interactions Study Guide

1. Explain the difference between contamination, infection, and disease. Describe a scenario

for all three terms.

• Contamination: Pathogens are introduced to your body but are not replicating ( Ex: Your friend coughs on you while you are talking to them)

• Infection: Pathogens are replicating on/inside your body (Ex: Bacteria from respiratory droplets gets in your mouth and begin to replicate)

• Disease: The body deviates from what is normal ( Ex: In two days you wake up with a sore throat)

2. Explain how we acquire our normal microbiota along with its benefits and potential

disadvantages.

• Resident: Part of our normal microbiota (In respiratory, GI, genitourinary tracts)-they help us by preventing growth of harmful organisms via microbial antagonism

• Transient: These microbes get on body surfaces through daily behaviors (Organisms you touch while you work, tough countertops or restroom doors)

3. Explain what is meant by “opportunistic pathogens” and how a normally harmless

organism can become problematic.

• These are microbes that are normally harmless but can cause chaos if the opportunity arises (S. aureus, E. coli, C. albicans)

4. Define pathogenicity and virulence. Why should these terms not be used

interchangeably?

• Pathogenicity: Can/Does the organism cause disease? (Yes or No)

• Virulence: The degree to which an organism causes disease Spectrum of pathogenicity

Just because something can cause disease doesn’t mean its virulent

5. What is a virulence factor? Give examples of some common virulence factors used by

bacteria and viruses.

• Virulence factors are molecules that help it takeover and multiply within a host

    (Ex: Exotoxin)

6. List and describe the steps a microbe must progress through to cause disease in a host.

a. What are the portals of entry? Which is most common?

• Most common portals of entry are skin, GI tract, Urogenital tract, respiratory tract, and parenteral

b. List and describe the different modes of transmission. Give examples of each.

• Indirect: Through a fomite (Kleenex) or Vehicle (Soil, water, air, food)

• Direct: Through Respiratory (coughing), horizontal or direct contact (kissing), and vertical. Vertical transmission can be prenatal (crosses placenta such as with Zika) or perinatal (through birth canal such as with an STI)

• Vector: Through Biological (mosquito) or mechanical (fly) means

• Parenteral: Through a needle/nail, has to penetrate the skin.

c. What are the different ways bacteria and viruses can attach and invade a host? of attachment?

Bacteria

• Adhesins such as capsules, pili, and fimbriae

Virus

• Docking proteins (Capsid and envelopes)

d. What strategies do microbes use to cause disease?

• They can use enzymes

• They can enter & multiply within cells

  

• They can enter under what is known as a “Trojan horse” where they enter a cell via a phagosome and before being degraded by the lysosome they escape within the cell

  

e. What are some strategies bacteria use to get past the host’s defenses?

• They can use antigenic variation which changes the surface molecules of the bacteria to evade recognition

• They can use exoenzymes such as Protease, Leukocidins, Hemolysins, coagulase, Hyaluronidase, and Kinase

• They can inhibit the complement system, preventing opsonization and lysis of bacterial cells

• They can use sticky capsules which makes it harder for immunes system to get rid of bacteria

• They can survive inside of phagocytes by breaking free from them as well as prevent phagolysosome formation

• They can form biofilm which provides protection for the bacteria

• They can use their flagella to outrun phagocytes

f. How do microbes exit the body?

• They can exit through the Respiratory tract (cough or sneeze)

• They can exit through the Genitourniary tract (STI/STD)

• They can exit through the Gastrointestinal tract (anus/defecation)

• They can exit through the skin (open lesions)

• They can exit through the blood (vectors or direct contact).

7. Compare and contrast endotoxins and exotoxins.

8. List and describe examples of exoenzymes used by bacteria to weaken a host.

• Coagulase: An enzymes that induces coagulation which the bacteria can use to protect themselves from phagocytes

• Protease: They destroy proteins

• Leukocidins: They target and damage white blood cells

• Hyaluronidase: This breaks down hyaluronic acid which is the “glue” that holds the cells together

• Streptokinase: Can break down clots after the bacteria is done hiding within the clot

• Hemolysins: Destroy red blood cells (RBC)

9. Describe the various ways we can classify infections

• Localized: Microbe is confined to one location upon entering the body

• Systemic: Infection spreads to several sites and tissue fluids, usually in the bloodstream

• Focal: Infection agents breaks loose from local infection & is carried to other tissue

• Mixed infection: Several agents establish themselves simultaneously at the infection site (at the same time)

  

Primary & Secondary infections: The initial infection (Primary infection). A secondary infection occurs when a primary infection is complicated by another infection caused by a different microbe. These are one after the other and do not occur at the same time.

• Acute infections: Come on rapidly and goes away quickly

• Chronic infections: Progress and persists over a long period of time

• Latent Infection: Characterized by a period of inactivity

10. Explain the difference between a sign and a symptom. Give common examples of signs

• Sign: Any objective evidence of disease as noted by an observer (Fever, septicemia, chest sounds, skin eruptions)

• Symptoms: Subjective evidence of disease as sensed by the patient (Chills, pain, malaise, fatigue, itching)

11. Describe the phases of an infection. Be able to sketch this information too.

• Incubation period: The time from initial contact with the infectious agent to the appearance of first symptoms

• Prodromal phase: When the earliest notable symptoms of infection appear (feeling off)

• Invasive phase: Infectious agent multiplies at high levels & exhibits its greatest virulence (Most severe signs and symptoms)

• Acme: The stage at which the disease reaches its peak intensity

• Decline phase: Signs and symptoms begin to subside & number of pathogens decrease

• Convalescent phase: Patient responds to infection and symptoms decline.