ID and Antimicrobial Therapy

Question 1

What might cause a falsely positive fever?

Answer 1

-drug induced: beta lactam abx (penicillins and cephalosporins) or phenytoin

Question 2

What might result in a falsely negative fever?

Answer 2

• aspirin (ASA)
• acetaminophen (APAP)
• NSAIDs
• corticosteroids

Question 3

What is the normal WBC count?

Answer 3

4500-10000 cells/mm^3

Question 4

What is a left shift?

Answer 4

increased WBC with increase in immature neutrophils (bands)

Question 5

How high might WBC be in a bacterial infection?

Answer 5

30000-40000

Question 6

What do immature bands indicate?

Answer 6

increased bone marrow response to infection

Question 7

What do bands > 10% indicate?

Answer 7

bacterial infection

Question 8

ESR

Answer 8

erythrocyte sedimentation rate

how far RBCs fall in 1 hour

Question 9

CRP Levels

Answer 9

0.5-1.0 normal
1.0-1.5 moderate inflammation
> 10 suggests infection

Question 10

Procalcitonin

Answer 10

• biomarker that becomes elevated during bacterial infection

- appears to reflect the severity of infection

Question 11

Gram Stain

Answer 11

• crystal violet stain
• add iodine to enhance stain
• alcohol decolorization
• safranin counterstain

Question 12

What is the difference between gram + and gram - bacteria? How do they stain?

Answer 12

• Gram +: thicker cell wall w/ lots of peptidoglycans; purple
• Gram -: thinner cell wall w/ more lipids, fewer peptidoglycans; pink

Question 13

What bacteria stain with acid-fast staining?

Answer 13

mycobacteria, nocardia

Question 14

What are gram stains routinely performed for (eg what types of infections)?

Answer 14

• CSF for meningitis
• urethral smears for STIs
• abscesses or effusions

Question 15

What is the gold standard for diagnosis and treatment of infections?

Answer 15

cultures

Question 16

Antibody and Antigen Detection

Answer 16

-detection and quantification of antibodies directed against a specific pathogen or its components

Question 17

How can anthrax be diagnosed?

Answer 17

PCR

Question 18

Bactericidal

Answer 18

kills sensitive organisms

Question 19

Bacteriostatic

Answer 19

inhibits bacteria growth but does not kill them

Question 20

What is meant by antimicrobial spectrum of activity?

Answer 20

• narrow: kills small # of narrow range of bacteria

- broad: kills many different kinds of bacteria

Question 21

Minimum Inhibitory Concentration

Answer 21

MIC = the lowest antimicrobial concentration that prevents visible growth of an organism after 24 hours of incubation

Question 22

Susceptibility Testing: MAcrodilution Method

Answer 22

• mix pathogen w/ serial dilutions of antibiotic
• incubate over night
• 1st clear tube is MIC

Question 23

Susceptibility Testing: MIcrodilution Method

Answer 23

-serial dilutions of several abx in a 96 well plate

Question 24

Susceptibility Testing: Kirby Bauer Disk Method

Answer 24

• paper discs impregnated with various abxs are placed on agar plate seeded with lawn of bacteria
• zone of growth inhibition around the discs is related to MIC (sensitivity and susceptibility)

Question 25

Susceptibility Testing: The E-test

Answer 25

• strip with various concentrations of abx placed on agar plate of bacteria
• as [abx] increases, bacterial growth is affected more

Question 26

Susceptibility Testing: What are the automated methods?

Answer 26

• Vitek system: photometric assessment of turbidity

- Microscan system: fluorogenic substrate hydrolysis as indicator of bacterial growth

Question 27

How are the peak serum concentration and MIC related?

Answer 27

peak serum concentration should be 2-4x MIC for the bacteria to be susceptible

Question 28

What factors increase abx resistance?

Answer 28

• overuse
• low dose, inadequate levels
• prolonged exposure
• inappropriate abx
• day care
• abx in animal feed??

Question 29

What must an antibiotic be able to do in order to have antimicrobial activity?

Answer 29

• penetrate cell
• reach target: cell wall, nucleus, ribosomes
• kill organism

Question 30

Name 4 methods of resistance.

Answer 30

• efflux pump
• decreased permeability
• drug inactivation
• altered target (eg penicillin binding proteins on cell surface)

Question 31

Decreased Permeability

Answer 31

• gram - have porin channels in cell walls that abx use to enter
• bacteria will close or reduce # of porin channels

Question 32

Efflux Pump

Answer 32

• the club bouncer

- abx gets in, but is identified as shady impostor and gets kicked out

Question 33

Drug Inactivation

Answer 33

abx gets into cell, but is inactivated (usually by enzymes like beta-lactamase)

Question 34

Altered Target

Answer 34

• example: macrolide abx gets in and normally works at ribosome; bacteria methylates its ribosomes to block abx activity
• example: bacteria alters penicillin binding proteins to block action of penicillins and cephalosporins

Question 35

Concentration Dependent Killing Rate

Answer 35

• more bacteria killed at higher [ ] of abx
• some aminoglycosides and FQs exhibit CDKR
• penicillins and other beta-lactams usually do not show CDKR

Question 36

Post-antibiotic Effect

Answer 36

• persistent effect of an abx on bacterial growth after the abx is removed from a bacterial culture
• most bactericidal abx exhibit PAE against susceptible pathogens

Question 37

What is an advantage of post-antibiotic effect?

Answer 37

allows for less frequent dosing

Question 38

What therapeutic steps are taken when treating infectious disease?

Answer 38

• empiric therapy: based on likely pathogen for site of infection, patient hx
• refine therapy based on culture and sensitivity results
• monitor therapeutic response and adjust therapy as needed