Antibiotic Resistance Flashcards
Resistance
when a previously susceptible organism is no longer inhibited by an antibiotic at levels that can be safely achieved clinically
what is intermediate resistance
can be treated with an increase from the standard dose
therapeutic index
The difference between dose necessary for treatment and that causing harm is usually large
what us intrinsic resistance
when all strains of a species are resistant (naturally)
What is MIC and what does it stand for
the minimum inhibitory concentration:
the lowest concentration fo antibiotic that completely inhibits the growth of a bacterium
what is MBC and what does it stand for
minimum bactericidal concentration:
the lowest dose that completely kills a bacterium
what is the antibiotic breakpoint
A concentration chosen for laboratory testing that will differentiate sensitive from resistant populations of bacteria
The breakpoint for a given antibiotic will vary for each of the species tested due to their differing intrinsic resistance/susceptbility
Used to simplify testing in the laboratory
Allows laboratories to test only one concentration rather than having to determine the MIC
what defines the breakpoint
- Distribution of MICs of target bacteria
- Achievable therapeutic concentration in tissue
- Maximum achievable concentration
acquired resistance
occurs when previously susceptible strains or species develops an increase in the MIC that takes it beyond the therapeutic range
- horizontal gene transfer ot mutation in the presence of a drug
Transposon
is a mobile genetic element that can move within or without a genome
Evolution of quinolone resistance
There are two genes involved -gyrA and parC
Point mutations in the genes change the affinity of the proteins for DNA
Mutation in one gene encodes low level resistance
Mutation in both genes encodes high level resistance
Conjugation I
Many bacteria have plasmids
- Accessory circular DNA
- Transmitted with the cell
Can encode virulence, metabolic functions and resistance determinants
Allows characteristics to be shared rapidly by bacteria
Transposons and integrons
Small segments of DNA that encode their own transmission
Many bacteria have these mobile genetic elements
Allow genome plasticity
May collect resistance determinants
What is a superbug?
Organism that has gained resistance to a critical antibiotic
Organism that has gained resistance to multiple antibiotics
Superbug
Methicillin Resistant Staph Aureus (MRSA)
Glycopeptide Resistant Staph Aureus (GISA)
Vancomycin Resistance Enterococcus (VRE)
Expanded spectrum beta-lactamases (ESBLs)
