Basic Concepts II

Question 1

1. Define and discuss the terms normal microbiota, commensal, opportunist and pathogen.

Answer 1

normal or endogenous microbiota: organisms that proliferate harmlessly in a particular site in healthy individuals
commensual (only micro-org benefits without harm or gain to the host), now understood as mutualisitic (benefits both)
opportunistic bugs cause infection only under specific conditions
pathogens are organisms that are able to evade host defenses and cause disease

Question 2

1. Explain the concept of carrier state.

Answer 2

carrier state may exist in an individual with an infection that is inapparent throughout its course or only during the incubation period, convalescence or post convalescence period

Question 3

2. Discuss the benefits derived from normal microbiota as well as the disadvantages.

Answer 3

benefits: block est. of exogenous pathogens and thus their ability to cause infection (some by production of product or maintain a pH), excrete vitamins, aid in digestion and can stimulate immune system
harmful: if spread to sterile parts esp. access to blood stream; can overgrow due to changes in environment or immune depression

Question 4

3. Describe the innate properties of the body and how non-specific immunity defends against infection.

Answer 4

epithelial barriers (skin, vaginal epithelium, respiratory epithelium, conjucntival epithelium, urinary and gastrointestinal epithelium)

secreted antimicrobials: lysozyme, secretory IgA

normal microbiota

phagocytes, NK cells, complement, fever

Question 5

4. Discuss how bacteria gain entry into the body and attach to target cells.

Answer 5

entry: ingestion, inhalation, trauma, needle stick, indwelling catheters, arthropod bite, sex

adhere via adhesins binding to specific receptors on the host cell surface (S. aureus lipteichoic acid, E. coli uses pili)

Question 6

5. Discuss the pathogenic actions of bacteria, including the role of virulence factors.

Answer 6

1. adhesions
2. biofilm formation-mats stuck to solid surface
3. quorum sensing- turn on biofilm formation, communication during aggregation to measure pop. density and make extracellular polysaccharides (impenetrable)
4. toxins i.e.. endotoxin LPS or exotoxins S. pyogens or S. aureus
5. degradative enzymes, esp hyaluronidase or collagenase, hemolysins or coagulase (move through extracellular space)
6. super antigens
7. induction of excess inflammation
8. evasion of phagocytic and immune clearance
9. capsule production
10. resistance to antibiotics
11. intracellular growth

Question 7

6. Explain why biofilms form and their role in disease

Answer 7

Bacteria use quorum sensing to turn on biofilm formation genes as well as modulate
the expression of other virulence factors. When bacteria aggregate, they communicate with
neighboring microbes by releasing and detecting signal molecules (autoinducers) in the
environment, allowing them to measure population density. They make copious amounts of extracellular polysaccharides resulting in a relatively impermeable three-dimensional structure.

Question 8

7. Discuss how bacteria are able to evade the immune system.

Answer 8

> polysaccharide capsules prevent attachment
antigenic variation- genetic recombination
prevent phagolysosme fusion or escape into cytoplasm

also: IgA protease, inhib chemotaxis, phagocytosis, lysosomal enzyme; intracellular replication

Question 9

8. Discuss how transmission occurs between hosts.

Answer 9

horizontal: person to person transmission
vertical: mother to fetus transmission

transmission can occur through contact, vector, fomite

Question 10

9. Penicillin cellular target and examples.

Answer 10

(B-lactam): interfere with synthesis of bacterial wall: dicloxacillin, ampicillin or pipercilllin

Question 11

10. Explain why there is such a problem with antimicrobial resistance today.

Answer 11

spread of resistance is enhanced by use of antimicrobials, especially those with broad-spectrum activity

use of antimicrobials in animal feeds can cause resistant microbe outbreak in beef or poultry

Question 12

11. Discuss strategies fro preventing and controlling antibiotic resistance.

Answer 12

reduce antibiotic pressure: eliminate unnecessary use and improve quality of use

Question 13

What is tropism?

Answer 13

organisms exhibit a tissue preference

Question 14

8. Cephalosporins target and examples.

Answer 14

B-lactam, interfere with synthesis of bacterial peptidoglycan cell wall, resistant to inactivation by B-lactamases: cephalexin, cefoxitin, ceftriaxone, cefepime, ceftaroline (generations on the basis of bacterial susceptibility

Question 15

8. Vacomycin target and examples.

Answer 15

glycopeptide, effective agains multi resistant Gram pos. orgs (i.e. MRSA), inhibits peptidoglycan at earlier step than penicillin

Question 16

8. Tetracylcine target and examples

Answer 16

target bacterial ribosome (30S subunit), broad spectrum antibiotics: tetracycline and doxycycline

Question 17

8. Aminoglycosides target and examples.

Answer 17

target 30S ribosome, protein synthesis inhibitors, effected against aerobic orgs, used in Gram neg aerobic bacteriaL gentamicin and tobramycin

Question 18

8. Macrolides target and examples

Answer 18

target 50S ribosome and inhibit protein synthesis: erythromycin and azithromycin

Question 19

8. Fluroquinolones target and examples

Answer 19

inhibit replication of bacterial DNA by interfering with DNA gyrase: ciprofloxacin against Gram neg, moxifloxacin against Gram neg and positive

Question 20

8. Trimethoprim- sulfamethoxazole target and examples

Answer 20

folic acid inhibitor, inhibits synthesis of tetrahydrofolic acid (combo drug), used against wide array of common Gram neg. bacteria and Staph.