Abx Resistance: Relationship to Clinical Use Flashcards
A drug that kills or inhibits the growth of microorganisms
Abx
Implies that an antimicrobial will not inhibit bacterial growth at clinically achievable concentrations
Resistant
Implies that an antimicrobial will inhibit bacterial growth at clinically achievable concentrations
Susceptible
Lowest concentration of antimicrobial that inhibits growth of bacteria
Minimal inhibitory concentration
Concentration of an antimicrobial that kills bacteria
Minimal bactericidal concentration
MIC that is used to designate between susceptible and resistant
Breakpoint
How is MIC determined in test tubes?
100mcg/mL is given to test tubes through serial dilutions to 0.4 mcg/mL; a standard amount o bacteria is added and incubated; the lowest concentration of abx with no bacterial growth (cloudiness) is the MIC
How is MIC determined on a well plate, and what are some advantages?
1 bacterium tested on each plate; each row has serial dilutions of a distinct antibiotic
(many abx per plate, less reagent and bacteria needed)
How is MIC measures automatically?
Machine will photometrically measure growth for each antimicrobial concentration well; determines an MIC within 6-8 hours
What is an advantage of automated testing?
antimicrobial susceptibilities can be determined at the same time the organism is identified
Test that can determine only susceptible vs resistant and not an MIC.
Kirby-Bauer Disk diffusion
MIC test that is measuring the diameter of growth inhibition and comparing to a chart.
Kirby-Bauer Disk diffusion
Tests that can determine MICs directly.
agar dilution and E-test
MICs are _____ while susceptible and resistant are ______ determinations
relative; absolute
Susceptible or resistant: MIC is lower than the breakpoint
susceptible
Susceptible or resistant: MIC is higher than breakpoint
resistant
How is breakpoint determined?
arbitrarily designated by a committee
T/F: MICs between different antibiotics may be compared to determine efficacy or potency of antibiotic.
F: breakpoint is different for each antibiotic
Where are half of abx used in N America?
agriculture
Why do doctors overuse abx? (3)
Patient expectations; diagnostic uncertainty; time
What patients are high risk for abx resistance? (3)
Immunocompromised, hospitalized, invasive devices (central venous catheters)
T/F: Abx are the ONLY drug that have direct public health consequences for persons other than the one who received the abx.
T
Although different antibiotics select different bacteria, they can select phenotypes that have resistance to other drugs, too. These microbes are called:
multidrug-resistant (MDR) organisms
Linezolid and erythromycin inhibit
protein synthesis
What 2 places would you find genes encoding resistance?
Plasmid or chromosome
In what cell structure might decreased permeability improve a microbe’s drug resistance?
Cell wall
What 3 reactions do microbial enzymes use to degrade drugs, especially aminoglycosides?
Sulfonation, phosphorylation, or esterifictation
B-lactamases are more potent in gram (positive/negative) bacteria.
negative
Type of B-lactamase most common in Klebsiella pneumoniae.
Carbapenemases (class A)
Type of B-lactamase capable of hydrolysing extended spectrum cephalosporins, penicillins, and aztreonam.
Extended spectrum
Type of B-lactamase most often associated with E. coli and Klebsiella pneumoniae.
Extended spectrum
T/F: ESBL and resistance for Aminoglycosides, ciprofloxacin and trimethoprim-sulfamethoxazole are often on same plasmid.
T
Pseudomonas spp. are often associated with what resistance mechanisms?
- Decreased Permeability
2. Efflux Pumps
What are 2 abx commonly effluxed?
Tetracyclines
Macrolides
Alterations to its gram positive cell wall protects Enterococcus from what drug?
vancomycin
What 2 microbes are associated with penicillin-binding protein?
Methicillin-resistant S. aureus (MRSA)
Penicillin-resistant S. pneumoniae
If altered, what enzyme in S. pneumo and many gram negative bacteria is protected from fluoroquinolones?
DNA gyrase
S. pneumoniae, Staph sp., N. gonorrhoeae, and enteric gram-negative rods are protected from tetracycline and macrolides through modifications to what cell organelle?
Ribosomes
T/F: MRSA is a problem that has been confined to hospitals
F: in communities as well
How does abx resistance affect healthcare (2)?
Increased costs and mortality
T/F: Surgical site infections with MRSA are not associated with increased mortality, but do seem to correlate with increased length of hospital stay.
F: Patients who have surgical sites with methicillin resistant cultures have been shown ~3x the mortality rate of those who are MSSA (and LOS is longer for those w MRSA)
Diabetic patients with peripheral vascular disease and chronic renal failure have demonstrated high level resistance to what type of abx?
Glycopeptides
Resistance to what drug has been demonstrated with prolonged vancomycin use due to persistent S.aureus infections?
Glycopeptides
S. pneumo resistance to what type of abx is on the rise?
Macrolides (such as azithromycin)
Resistance to fluoroquinolone correlates with:
its frequency of use
What is the most common infection caused by community-acquired resistant E. Coli?
UTI’s
Bacteria picks up free DNA from environment.
transformation
DNA is transferred to bacterial by viral delivery.
Transduction
