Antibiotics 3 Flashcards
What is the action of aminoglycosides?
Binds to 30S component of ribosome close to the reading frame to distort the reading frame - results in the wrong amino acid being incorporated or pre mature termination
What are the mechanisms for aminoglycoside resistance?
enzyme modification, modification to outer membrane, efflux (pump the antibiotic out), ribosomal mutation
How are aminoglycosides enzymatically modified to inhibit their action?
acetylation, adenylation or phosphorylation
Where are the enzymes for modification of aminoglycoside located?
In the periplasm of gram negative bacteria - this prevents the antibiotic from entering the cytoplasm
What are the mechanisms of resistance to antimicrobial agents?
drug inactivation, altering target, reduce access to target, failure to activate drug precursor
What is an example of drug inactivation?
Beta lactamase in psedumonas against beta lactams or enzymatic modification against aminoglycosides
What is an example of altering the target?
Altering the PBP in MRSA to resist beta lactam, altering the D-ala to D-lac in enterococci to resist vancomycin, or overproducing peptidoglycan in VISA to resist vancomycin
What is an example of reducing access to the target?
modification to outer membrane or efflux against aminoglycosides
What is an example of failure to activate precursor?
TB that doesn’t express the gene kat so can’t activate isoniazid
Why is TB treated with 4 different antibiotics?
Because M. tuberculosis is acid fast the only way resistance can occur is through mutation. By treating with 4 different antibiotics at the same time it reduces the time so there is less time for a mutation to occur that makes the TB resistant
What does multi-drug resistant mean?
That the TB is already resistant to 2 of the 4 initial antibiotics used
What does extensively drug resistant mean?
That the TB is resistant to all of the 4 first line drugs
What is the difference between intrinsic resistance and acquired resistance?
Intrinsic resistance is where a property of the bacterium makes it resistant to the antibiotic e.g. all gram negative bacteria are resistant to vancomycin because it can’t get through the cell wall. Whereas acquired resistance is when a bacterium should be susceptible to an antibiotic but isn’t because it has become resistant through gene transfer or mutation
What are the three kinds of horizontal gene transfer?
Transformation, transduction, conjugation
What is the process of transformation?
The DNA donor dies and the DNA is taken up by a competent cell and incorporated into the chromosome by homologous recombination - donor and recipient have to be closely related
