MicroBiology

Question 1

Colonization

Answer 1

presence of bacteria on a host without or inducing disease. Ex: Staph aureus colonization in the nose

Question 2

Infection

Answer 2

An organism abnormally present and multiplying in host tissues usually leading to an immune response

Question 3

Disease

Answer 3

Impairment of physiologic function with associated signs and symptoms.

Question 4

Infectivity

Answer 4

Impairment of physiologic function with associated signs and symptoms.

Question 5

Pathogenicity

Answer 5

Ability of microbe to cause disease

Question 6

Virulence

Answer 6

Degree of pathogenicity within a specified group which depends on both bacterial and host factors

Question 7

Gram-positive cell wall

Answer 7

Purple stained; Outside to inside: Thick peptidoglycan cell wall (with teichoic acid), membrane

Question 8

Gram-negative cell wall

Answer 8

Pink stain; Outside to inside: Lipopolysachharide (endotoxin), membrane, small petidoglycan wall, membrane

Question 9

Acid-fast stain

Answer 9

Acid-fast organisms like Mycobacterium contain large amounts of fatty acids, waxes, and complex lipids within their cell walls called mycolic acids (resist staining by ordinary methods such as a gram stain).

Question 10

Coagulase test

Answer 10

Used to differentiate Staphylococcus aureus (positive) from coagulase negative Staphylococcus.

Coagulase is an enzyme produced by S. Aureus that converts (soluable) fibrinogen in plasma to (insoluble) fibrin.

Question 11

Hemolysis on blood agar

Answer 11

Alpha: partially breaks down the RBCs and leaves greenish color behind, due biliverdin

Beta: breaks down the red blood cells and hemoglobin completely, leaving a clear zone around the bacterial growth

Gamma: if the organism does not produce hemolysis and does not break down the blood cells, no clearing will occur

Question 12

Indole test

Answer 12

Used to determine the ability of the organism to convert tryptophan into indole

Question 13

Kirby-Bauer

Answer 13

A test of the antibiotic sensitivity of bacteria; uses antibiotic disks to test whether particular bacteria are susceptible to specific antibiotics.

Question 14

Bacterial virulence factors

Answer 14

1)Adherence, 2) surface modifications, 3) invasion, 4) modify the host

Question 15

Endotoxins

Answer 15

Within the bacteria; LPS in gram neg bacteria

Question 16

Exotoxins:

Answer 16

Expressed externally to bacteria; usually protein in nature

Question 17

Major means of bacterial transmission:

Answer 17

1. Contact
2. Food and water
3. Airborne
4. Vector-based
5. Perinatal
6. Nosocomial

Question 18

Catalase test

Answer 18

Used to differentiate staphylocci (catalase-positive) from streptococci (catalase-negative)

Small amount of bacterial isolate is added to H202. Bubbles indicate positive.

Question 19

Describe the distinctive properties that define a virus:

Answer 19

Obligate intracellular parasite containing DNA or RNA

Question 20

Obligate intracellular parasite:

Answer 20

Contains DNA or RNA; requires living cells for replication (uses host energy sources, ribosomes, enzymes for replication); small infectious agents (20-30nm)

Question 21

Define virion:

Answer 21

A single infections unit, composed of nuclei acid core covered by capsid, the protein coat.

Question 22

The principle events of viral replication (list 8):

Answer 22

1) Attachment to cellular receptors (tropism)
2) Penetration by translocation, endocytosis, or fusion
3) Disassembly
4) Transcription
5) Translation
6) Replication
7) Assembly
8) Release

Question 23

List the 5 types of viral infection and their potential consequences for the host:

Answer 23

1) enteric, 2) neurotrophic, 3) dermotropic, 4) respiratory, 5) systemic

Question 24

Describe the general steps of viral pathogenesis:

Answer 24

1) Entry into host,
2) Primary replication,
3) Spread,
4) Cell/tissue tropism,
5) Secondary replication,
6) Cell injury and persistence,
7) Host immune response

Question 25

Distinguish between innate and acquired resistance to viral infections:

Answer 25

Innate: natural barriers, chemical conditions, nonspecific host defenses, interferons

Acquired: T and B cells

Question 26

Describe the role of interferon in fighting viral infections

Answer 26

Type1 (viral) alpha (leukocyte): produced by viral-infected leukocytes

Type 1 (viral) beta (fibroblast): produced by virus-infected fibroblasts, or infected epithelial cells

Type 2 (immune) gamma: produced by infected T cells and NK cells

Question 27

Describe the routine lab procedures used to diagnose viral infections:

Answer 27

1) Histology
2) Culture
3) Direct fluorescent antibody
4) Nucleic acid detection by PCR

Question 28

Describe how HIV depleates CD4 cells

Answer 28

Virus replicates at extremely high rates

Question 29

Describe what constitutes an antigenic drift and what differentiates it from an antigenic shift, using influenza as and example:

Answer 29

Antigentic shift (outbreaks): genetic reassortment between different strains or across species

Antigentic drift: point mutations in surface proteins that alter antigen structure

Question 30

Identify the members of the herpes family of viruses:

Answer 30

Disease (and virus):

Herpes simplex (HSV1 & 2);

Chickenpox & shingles (varicella zoster);

CMV infections and mononucleosis (cytomegalovirus);

EBV infectious mononucleosis, associated with Burkitt’s lymphoma (Epstein-Barr virus)

Question 31

Describe the mechanism of latent viral infection, using herpes simplex as an example:

Answer 31

• Restricted expression of viral genome, few if any changes in the infected cell, no virions produced
• infection held in check by immune surveillance
• immunosuppression (AIDS, organ transplant, HCT) ->DZ
• HSV-1 and -2

Question 32

Pandemic

Answer 32

Worldwide outbreak, occurs every 10-20 year, usually due to antigenic shift

Question 33

Epidemic

Answer 33

Regional outbreak, occurs every few years, due to major antigenic drift