Basic concepts

Question 1

Pathogenicity vs virulence

Answer 1

Pathogenicity= ability to cause disease
Virulence= extent of disease

Question 2

Pathogen

Answer 2

organism causing damage and disease (symptoms / signs of illness) via interaction with host

Question 3

List five broad classes of human pathogens

Answer 3

viruses
bacteria
fungi
protozoa
helminths

Question 4

Gram positive organisms stain ______ with Gram staining whereas gram negative organisms stain ______

Answer 4

purple/blue; pink/ red

Question 5

Gram positive organisms have a thicker ________ layer than Gram negative organisms. This blocks the decolorization step of the Gram staining process

Answer 5

peptidoglycan (murein)

Question 6

List the basic steps in Gram staining protocol

Answer 6

1. fixation
2. stain with crystal violet
3. iodine treatment
4. decolorization
5. safranin counter stain

Question 7

Findings of intracellular gram negative diplococci within PMNs on gram stain of urethral discharge in symptomatic men is diagnostic for ________

Answer 7

Neisseria gonorrhoeae

Question 8

List features of Gram positive bacteria

Answer 8

• two layers: thick peptidoglycan layer; cytoplasmic membrane
• teichoic acids
• adhesion to host cells by adhesions and teichoic acids

Question 9

List features of Gram negative bacteria

Answer 9

• three layers: outer membrane; thin peptidoglycan; inner membrane
• endotoxin/ LPS
• periplasmic space
• porins
• attachement to host cells by fimbriae, adhesins

Question 10

Describe phases of standard bacterial growth curve

Answer 10

1. Lag phase: little cell growth/ division as cells adapt
2. Exponential phase: maximal division rate
3. Stationary phase: nutrients exhausted, waste products accumulate, new cells= dying cells
4. Death phase: number of nonviable cells > viable cells

Question 11

Mesophiles grow best at ________ degrees celsius and include most human pathogens

Answer 11

20-45 C

Question 12

_______ grow at temperatures below 20 C and are a major concern in _______ and blood products

Answer 12

Psychrophiles; refrigerated foods

Question 13

Thermophiles grow at temperatures of 45-60 C and are a concern in _________

Answer 13

food processing/ canning

Question 14

________ grow at temperatures greater than 60 C

Answer 14

Stenothermophiles

Question 15

Why are anaerobes unable to grow in the presence of oxygen?

Answer 15

lack enzymes to detoxify reactive oxygen species

Question 16

most human pathogens are ________ for oxygen

Answer 16

facultative

Question 17

_______ require reduced oxygen levels for maximal growth

Answer 17

Microaerophiles

Question 18

_______ grow best under conditions of increased carbon dioxide

Answer 18

Capnophiles

Question 19

Distinguish plasmids from transposons

Answer 19

• Plasmids: 5-100 genes passed during cell division or transferred between bacteria during conjugation or transformation
• Transposon: 1-10 gene element on plasmid or chromosome that can move to other sides in DNA; does not replicate independently

Question 20

Distinguish: transformation, transduction, and conjugation

Answer 20

Transformation – mediated by free (naked) DNA
Transduction – mediated by bacterial virus (bacteriophage)
Conjugation – mediated by transfer apparatus, e.g., pilus

Question 21

One way of maintaining transferred DNA is integration into a replicating DNA molecule via _______

Answer 21

genetic recombination

Question 22

Distinguish generalized transduction from specialized transduction

Answer 22

• generalized transduction: mediated by lytic phase; any portion of degraded bacterial DNA can be repackaged into assembling phage head
• specialized transduction: mediated by lysogenic phage, imprecise excision carries along bacterial DNA from areas adjacent to phage integration site

Question 23

Define lysogenic conversion

Answer 23

lysogenic phage infection changes the phenotype of the host bacterium, sometimes incurs new virulence factors. Ex diptheria toxin, cholera toxin

Question 24

Describe antigenic variation as a mechanism of escaping host defenses.

Answer 24

Organism expresses different phenotypes- homologous proteins-> antigenic variation. Change pilus so host response is no longer effective. Evade adaptive host response

Question 25

List three antibiotic classes that inhibit cell wall synthesis

Answer 25

penicillins, cephalosporins, vancomycin

Question 26

List three antibiotic classes that inhibit protein synthesis

Answer 26

tetracyclines, aminoglycosides, macrolides

Question 27

List the antibiotic class that inhibits DNA synthesis

Answer 27

Fluroquinolones

Question 28

List the antibiotic that is a folic acid inhibitor; contains two synergistic components

Answer 28

TMP-sulfa

Question 29

List three broad strategies for controlling antibiotic resistance

Answer 29

1. reduce selective pressure: eliminate unnecessary use and improve quality of use
2. improve nosocomial infection control: aseptic technique, surveillance
3. aggressive control of outbreaks: identify, isolate