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Microbiology > Antibiotic Susceptibility Testing > Flashcards

Antibiotic Susceptibility Testing Flashcards

1
Q

Bacteriostatic

A

Inhibits growth but does not kill

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2
Q

MIC

A

Minimum Inhibitory Concentration of an antimicrobial agent which inhibits the growth of microorganism. Should be determined for each antimicrobial to be used in therapeutics

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3
Q

Bacterial Resistance Mechanisms to Antibiotics

A
  • Enzymes that inactivate or alter the antibiotic
  • Barrier to entry (cell wall or outer membrane) Overproduces targeted sites
  • Porins (decrease or prevent the uptake of the antibiotic)
  • Efflux (pump the antibiotic out of the cell)
  • Alter the antibiotic attachment site
  • Produce a different enzyme that substitutes for the targeted one
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4
Q

Intrinsic Resistance

A
  • Vancomycin is too large to cross the outer membrane of GN (they are inherently resistant)
  • Anaerobes are resistant to aminoglycosides
  • Almost all GNR express chromosomal beta-lactamases
  • Enterococcus spp. target sites have low affinity for many antibiotics
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5
Q

Extrinsic Resistance

A
  • Chromosomal mutations within the organism
  • Nonchromosomal genetic elements transfers genetic info. between different genera and species (plasmids and transposons)
  • DNA from environment
  • Bacteriophages
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6
Q

Inhibitors of Cell Wall Synthesis

A

Beta-Lactam Class: Penicillins, Cephalosporins, Monobactam, Carbapenams

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7
Q

Bacterial Resistance Mechanisms against Beta-Lactams

A
  • Produce degradative enzymes (Beta-Lactamases, Extended-spectrum beta-lactamases, Carbapenemase production)
  • Alter the attachment site (PBP)
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8
Q

Extended-Spectrum Beta-Lactamases (ESBL)

A

Detection of ESBL: all penicillins, cephalosporins, and aztreonam should be reported as resistant

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9
Q

Carbapenemase

A
  • Use to treat ESBL
  • First seen in Klebsiella pneumoniae (aka Klebsiella pneumoniae carbapenemases (KPC)
  • Now produced by others in the Enterobacteriaceae family, resistant to all β lactams, and many other non-β-lactam molecules
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10
Q

Penicillin Binding Proteins

A
  • Enzymes responsible for building cell wall
  • Intrinsic resistance: does not have the required PBP for beta-lactam drug
  • Extrinsic resistance: Overproduction of the targeted PBP, Point mutation in the PBP gene that causes a decrease PBP affinity, Acquired foreign gene codes for a structurally different PBP
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11
Q

Inhibitors of Protein Synthesis

A

Aminoglycosides, Macrolide-Lincosamide-Streptogramin (MLS group), Oxazolidinones, Chloramphenicol, Tetracyclines

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12
Q

Inhibitors of DNA & RNA synthesis

A

Fuoroquinolones, Metronidazole, Rifampin

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13
Q

Inhibitors of Other Metabolic Processes

A

Sulfonamides, Trimethoprim, Nitrofurantoin

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14
Q

Acid Fast Bacteria

A
  • Primary treatment: Streptomycin, Isoniazid, Rifampin, Ethambutol, Pyrazinamide
  • Secondary treatment: Ethionamide, Capreomycin, Ciprofloxacin, Ofloxacin, Kanamycin, Cycloserine, Rifabutin
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15
Q

Tetracyline Side Effects

A

Causes discolored teeth and affect bone development in children

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16
Q

Amphotericin B Side Effects

A

Nephrotoxicity, irreversible damage to kidney.

17
Q

Rifampin Side Effects

A
  • Orange body fluid(urine and tears)
  • Soft contact lens may be permanently discolored
18
Q

Cloramphenicol Side Effects

A

Bone marrow suppression, aplastic anemia, and gray baby syndrome (neonate with an immature liver)

19
Q

Quinolones Side Effects

A

May damage cartilage in patients younger than 18 yrs. and pregnant women

20
Q

Selective Reporting

A

A cascade system in which the test result of some antimicrobial agents are reported only if the test organisms is resistant to a particular drug

21
Q

E-test

A

One side of the strip contains the antimicrobial conc. gradient and the other contains a numeric scale that indicates the drug conc., After incubation, MIC is read where the growth inhibition edge intersects the strip

22
Q

Clindamycin Resistance in Staphylococci

A

Erythromycin disk placed next to Clindamycin disk, Flattening of the zone around clindamycin, D-shaped pattern, Inducible resistance

23
Q

Beta-lactamase Tests

A

Chromogenic cephalosporin nitrocefin discs used

If the bacteria produces beta-lactamase, Pink or red color develops

24
Q

Detection of Vancomycin Resistant Enterococci

A
  • Vancomycin screening agar plate
  • Contains brain heart infusion (BHI) agar
  • Supplemented with 6 μg/mL
25
Q

Automated Susceptibility Test Systems

A
  • Vitek 2 AST System
  • Contains 64 wells with multiple concentrations of up to 22 antibiotics that are mixed with a suspension of the bacteria WalkAway System
  • Uses the broth microdilution panel format that is manually inoculated with a multi prong device, then automatically incubated and read

Microbiology (11 decks)

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