29. Antimicrobial Susceptibility Testing Flashcards
Quantitative measure of the susceptibility of a bacterial isolate to an antimicrobial agent
MIC
Lowest concentration of antibiotic to kill the bacterial isolate in vitro
Minimal bactericidal concentration (MBC)
Give the standards for broth dilution, agar dilution, and diffusion
Broth dilution: 5x10^5 CFU/mL
Agar dilution: 1x10^4 CFU/mL
Diffusion: 1x10^8 CFU/mL
A chemical substance produced by a microorganism that can inhibit the growth or kill other microorganisms
Antibiotic
An agent that kills or supresses growth of microorganisms
Antimicrobial
Agents that prevent replication but does not kill the target
Bacteriostatic
Agents that result to cell death
Bacteriocidal
Examples of bacteriostatic agents
Macrolides
Tetracyclines
Sulfonamides
Examples of bacteriocidal agents
β-lactams
Vancomycin
Fluoroquinolones
Rifampin
Mechanisms of antimicrobial action
- cell wall inhibitors
- cell membrane inhibitors
- protein synthesis inhibitors
- other metabolic pathways inhibitors (folate metabolism)
Cell wall synthesis inhibitors
- β-lactams
- carbapenems
- vancomycin
Examples of β-lactams
Penicillin
Cephalosporins
Examples of carbapenems and monobactams
Imipenem
Meropenem
Aztreonam
Antibiotic that works only on growing cells
Penicillins
Penicillins are synergistic with
Aminoglycosides
Antibiotic that stops transpeptidation which causes the cell wall of bacteria to develop weak stops
Penicillins
Side effect if imipenem is overdosed
CNS toxicity
Antibiotics that are broad spectrum, low MICs, but expensive
Carbapenems
Mechanism of penicillins
Binds with penicillin-binding protein which stops transpeptidation
Mechanism of action of Vancomycin
Stops gram-positive cell wall peptidoglycan chain formation
Vancomycin is bactericidal for
Staphylococci
Streptococci
Vancomycin is bacteriostatic
Enterococci
Antibiotics that are cell membrane inhibitors
Colostin
Amphotericin
Polymyxin
CAP
Polymyxin B and Colistin are active against
Gram-negative bacteria
Mechanism of action of Polymyxin B and Colistin
Disrupts the gram-negative cell membrane
Specific bacteria that Polymyxin B and Colistin are effective against
P. aeruginosa
Antibiotics that are DNA/RNA inhibitors
Fluoroquinolones
Metronidazole
Nitrofurantoin
Rifampin
Examples of fluoroquinolones
Ciprofloxacin
Levofloxacin
Mechanism of action of fluoroquinolones
Inhibits DNA gyrase and/or topoisomerase —> prevents DNA unwinding and blocks DNA synthesis
Mechanism of action of Metronidazole
Damages DNA and other molecules directly
Mechanism of action rifampin
Prevents RNA synthesis by inhibiting the DNA-dependent RNA polymerase
Antibiotic that has intracellular activity
Rifampin
Antibiotics that are protein-synthesis inhibitors
Clindamycin Linezolid Aminoglycosides Macrolides Quinupristin/dalfopristin Tetracyclines
CLAMQT
Examples of macrolides
Azithromycin
Clarithromycin
Erythromycin
Dirithromycin
ACED
Examples of aminoglycosides
Tobramycin
Amikacin
Neomycin
Gentamicin
TANG
Examples of Tetracyclines
Doxycycline
Minocycline
Tetracycline
DMT
Antibiotics that are inhibitors of intermediate metabolism
Trimethoprim
Sulfamethoxazole
Mechanism of action of Trimethoprim and Sulfamethoxazole
Stops folate synthesis
Lowest concentration observed to inhibit growth of the isolate in vitro
Minimal inhibitory concentration (MIC)
