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Microbiology Exam 1 > Antibiotics > Flashcards

Flashcards in Antibiotics Deck (34):
1

Antibiotic Susceptibility Testing: Bactericidal Activity

-Level of antimicrobial activity that KILLS
-Lowest concentration of antibiotic that kills 99.9% = minimum bactericidal concentration (MBC)

2

Antibiotic Susceptibility Testing: Bacteriostatic Activity

-Level of antimicrobial activity that INHIBITS GROWTH
-Lowest concentration of antibiotic that inhibits growth = minimum inhibitory concentration (MIC)

3

Antibiotic

Isolated in NATURE

4

Antimicrobial

Synthesized in a LAB

5

Bacteriostatic

Inhibit growth

***Used when host defenses can be counted on

6

Bactericidal

Killing

***Used during invasive infection: bacteremia, meningitis, endocarditis

7

Broad-Spectrum Antibiotic (Definition and Advantages/Disadvantages)

Effective against a large variety of bacteria

Advantage: increased likelihood of effectiveness agaisnt bacterial infection of UNKNOWN etiology

Disadvantage: increased likelihood of disrupting normal biota

***Prescribed when you are unsure of the bacteria that is infection and want to start treatment immediately

8

Narrow-Spectrum Antibiotic (Definition and Advantages/Disadvantages)

Effective against only a small subset of bacteria

Advantage: avoids disruption of the normal microbiota

Disadvantage: Must have SPECIFIC DISEASE causing bacteria identified in order to choose abx

***Used in non-emergent cases

9

Do antibiotics cause antibiotic resistance?

No; they select against sensitive bacteria and for resistant bacteria, which allows for survival of bacteria that have gained a rare mutation/genetic acquisition

10

Empiric Therapy

Generally BROAD SPECTRUM
-Treatment while waiting for lab results

11

Targeted Therapy

NARROW SPECTRUM
-Refined treatment

12

Antibiotic resistance is ____ at an alarming rate; Antibiotic discovery is ____ at an alarming rate

Accelerating; Decelerating

13

Antibiotic Resistance (General Mechanisms)

1. Breakdown of an antibiotic (e.g. Hydrolysis)
2. Chemical modification of an antibiotic (e.g. Methylation or Phosphorylation)
3. Alteration of the Target (Mutations and/or gene acquisition)
4. Altered permeability, decreased influx, or increased efflux (e.g. pumps to pump out abx)
5. Lack of target

14

Minimum Inhibitory Concentration (MIC) tests

1. Disk-diffusion assay (e.g. Kirby-Bauer Test)
-Abx migrates out from disc from high concentration to low concentration; can measure zone of inhibition/clearing to get MIC
2. E-Test (same thing, except with strips that have a tapering of high to low concentration of abx)
3. Broth Culture (measures both MIC and MBC; see subsequent slide)

15

Broth Culture

Measures both MIC and minimum bactericidal concentration (MBC)
-Measures DENSITY of bacteria based on how much light comes through the test tube

***MIC measures inhibition of growth via visualization in test tube

***MBC measures killing of bacteria via growth (or lack of growth) on an agar

16

Cell Wall Active vs Membrane Active Antibiotics

Cell Wall Active:
-Disrupts PEPTIDOGLYCAN synthesis
-ONLY effective against ACTIVELY DIVIDING bacteria

Membrane Active:
-Disrupts or interferes with MEMBRANE integrity/synthesis
-Effective against RESTING AND ACTIVELY DIVIDING bacteria

17

Beta-lactams

***Bactericidal***
-Inhibit cell wall synthesis

e.g. Penicillins,Cephalosporins, Cephamycins, Carbapenems, Monobactams

18

Beta-Lactams (Mechanism of Action)

Bind the active site transpeptidases (i.e. Penicillin Binding Proteins (PBP)), preventing them from crosslinking peptidoglycan together

19

Resistance to Beta-Lactams (4 mechanisms)

1. Altered transpeptidases (e.g. mutation: decreased abx affinity)
2. Altered outer-membrane permeability (e.g. mutation in porins)
3. Presence of efflux pumps
4. Chemical modificaiton of antibiotic (Beta-Lactamase)

20

Vancomycin (Sensitive Bacteria)

***Bactericidal***

-Vancomycin binds two D-ala residues on the end of the peptide chains, PREVENTING them from interacting with TRANSPEPTIDASE
-Cross-links cannot be formed = cell death

21

Vancomycin (Resistant Bacteria)

-The last D-ala has been REPLACED by a D-LACTATE, so Vancomycin cannot bind
-Cross-links are formed and cell wall is successfully made

22

Bacitracin

***Bactericidal***
-Interferes with dephosphorylation in cycling of lipid carier that transfers peptidoglycan subunits to the growing cell wall

23

Protein Synthesis Inhibitors (3 of them)

Tetracyclines, Aminglycosides, Macrolides

24

Tetracycline

***Bacteriostatic***
-Broad Spectrum
-Bind 30s subunit
e.g. Tetracycline, Doxycycline

Mnemonic: Both have cycline in the name

25

Aminoglycosides

***Bactericidal***
-Oxygen-dependent (INEFFECTIVE against intestinal pathogens)
-Bind 30s subunit
e.g. Gentamicin, Kanamycin

26

Macrolides

***Bacteriostatic***
-Used as an alternative for penicillin allergies
-Bind 50s subunit
e.g. Erythromycin, Azithromycin

27

Nucleic Acid Synthesis Inhibitors (3 of them)

Quinolones, Rifampin/Rifabutin, Metronidazole

28

Quinolones

***Bactericidal***
-WIDELY USED
-MOA: inhibits DNA replication, recombination, and repair via DNA topoisomerase type II (gyrase) or topoisomerase type IV

29

Rifampin/Rifabutin

***Bactericidal***
-MOA: binds to DNA-dependent RNA polymerase and inhibits initiation of RNA synthesis

30

Metronidazole

***Bactericidal***
-MOA reduced by bacteria = toxic compounds that damage DNA

31

Antimetabolites (MOA and examples)

***Bacteriostatic***

MOA: Target folate metabolism, preventing synthesis of purines and thymidine, and ultimately preventing DNA/RNA synthesis

e.g. Sulfonamides and Trimethoprim (***Work together SYNERGISTICALLY)

32

Sulfonamides prevent formation of ______

Dihydrofolic Acid (from Dihydropterate Diphosphate and PABA)

33

Trimethoprim prevents formation of ______

Tetrahydrofolic Acid (from Dihydrofolic Acid)

34

MIC vs MBC

MIC: lowest concentration of antibiotic that INHIBITS growth

MBC: lowest concentration of antibiotic that KILLS 99.9%