antibiotic resistance Flashcards
define resistance
when a previously susceptible organism is no longer inhibited by an antibiotic at levels that can be safely achieved clinically
define intermediate resistance
this is resistance that can be treated with an increase from the standard dose
define therapeutic index
Difference between dose necessary for treatment, and minimum dose causing harm.
Define minimum inhibitor concentration (MIC) + minimum bactericidal concentration (MBC).
Lowest concentration of an antibiotic that completely inhibits the growth of a bacterium.
Lowest concentration of an antibiotic that completely kills a bacterium.
What is the MBC of bacteriostatic drugs ?
They do not have one (they do not kill the bacteria)
Define antibiotic breakpoint.
What factors might change the antibiotic breakpoint.
-The antibiotic break point is the Concentration chosen for laboratory tests which will differentiate sensitive from resistant populations of bacteria (makes it easier for labs, allows them to test only one concentration rather than having to determine the MIC)
-The breakpoint of a given antibiotic will be different for different species because they will have different intrinsic resistance/susceptibility.
what 3 factors will determine the breakpoint of the antibiotic?
- the distribution of the MICs of the target bacteria
- achievable therapeutic concentration in tissue
- maximum achievable concentration
what is streptococci resistant to and why?
Streptococci are naturally resistant to aminoglycosides because their MIC is higher than the toxic concentration
what is pseudomonas spp. naturally resistant to and why?
Pseudomonas spp. normally resistant to beta-lactams because intrinsic beta lactamases, although these can be overcome by design
what is mycoplasma spp. naturally resistant to and why?
resistant to all beta lactams because the cell has has no peptidoglycan which beta lactams act against
what is enterobaceriaciae naturally resistant to and why?
Enterobacteriacae are all resistant to metronidazole because they are facultative anaerobes, so normally grow in aerobic conditions
define acquired resistance?
this occurs when a previously susceptible strain or species develops an increase in the MIC that takes it beyond the therapeutic range.
what are the 6 main mechanisms of resistance?
1) enzymatic inactivation
2) enzymatic addition
3) impermeability
4) efflux
5) alternative pathways
6) altered target
Identify an enzyme responsible for the process of enzymatic inactivation by destruction.
Beta lacatamases
Expanded spectrum beta lactamases
Beta lactams (including cephalosporins) are effected by this.
what class of antibiotics affected by the process of enzymatic inactivation by addition.
aminoglycosides