Mechanisms of Antibiotics and Antibiotics Resistance Flashcards
What are the 4 types of resistance?
mutational resistance, natural (intrinsic) resistance, transferable resistance, induced resistance
What are the two types of transposable elements and what do they have in common?
The two types of transposable elements are transposons and insertion sequences. They have common inverted short sequences (IR) flanking them, which are essential for inserting on another part of the chromosome
How are plasmids different from transposons/insertion sequences?
Plasmids are ds circular DNA that contains 1-2 genes and can self-replicate. Transposons and inserted sequences must exist within a replicon because cannot self-replicate
What are integrons?
They are non-mobile DNA elements in bacteria that normally exist within transposons and acquire gene cassettes that contain antibiotic resistance genes. Integons have their own promotor sequences.
What do insertion sequences encode?
encode only functions involved in insertion
Seven mechanisms of Antibiotic Resistance
- Enzymatic inactivation
- Decreased permeability
- Efflux
- Alteration of target site
- Protection of target site
- Overproduction of target
- Bypass of inhibited process
Which beta-lactam antibiotic serves as a back-up drug in case bacteria are resistant to the others and will be extremely problematic if there’s resistance to it?
Carbapenems: most powerful b-lactam antibiotic
What enzymes do b-lactam antibiotics inhibit?
transpeptidase, carboxypeptidase, and endopeptidase
What have bacteria acquired to resist b-lactam antibiotics?
They can secrete an enzyme called b-lactamase that will require a serine or zinc at active site to hydrolyze the b-lactam ring.
What are the 5 types of b-lactamases?
- narrow spectrum b-lactamases
- Extended spectrum b-lactamases (ESBL) against 3rd generation cephalosporin
- amp C production (some enteric bacteria encode this in their chromosome -natural resistance;ampC is inducible)
- carbapenemase production (scary b/c carbapenem is our backup beta-lactam abx)
- major outer membrane protein modification
If patient has bacteria with extended spectrum b-lactamases will also put in isolation like someone with MRSA, why?
b/c you don’t want these resistance to spread.
Patients with ESBLs (extended spectrum b-lactamases) are treated with
Carbapenems
How does MRSA occur? Which gene expression plays a role?
by altering target sites via making modified transpeptidase (a way gram + bacteria can evade b-lactam antibiotics in addition to making b-lactamase). Expression of mecA gene plays a role in MRSA.
What is the mechanism of action of beta-lactam antibiotics?
They mimic the D-ala-D-ala residues causing penicillin binding proteins (transpeptidases) to bind to antibiotics as opposed to crosslinking and building the bacterial cell wall.
What are the 4 main classes of beta-lactam abx?
- penicillins
- cephalosporin
- monobactams
- carbapenem
List the 6 antibiotics that inhibit protein synthesis and state whether they are bacteriocidal or bacteriostatic
- tetracycline -bacteriostatic
- aminoglycoside -bacteriocidal
- macrolid -bacteriostatic
- chloramphenicol -bacteriostatic
- clindamycin -bacteriostatic
- linezolid -bacteriostatic
What’s the main reason that an antibiotic may at some times be bacteriostatic and at other times be bacteriocidal
It depends on the dosage of the abx in comparison to the minimum inhibitory concentration.
ESBL (extended spectrum beta lactamases) and KPC (klebsiella pneumonia carbenpenmases) -compare and contrast their spectrum of activity and most common organisms
-Spectrum of activity
ESBL -affect most b-lactam abx except carbapenem
KPC -affect even carbapenem (largest abx resistance spectrum)
-Most common organisms
ESBL -e. coli, proteus, klebsiella
KPC -klebsiella and many gram negative species
What is the mechanism of resistance responsible for VRE?
altering cell wall precursor target site; normally, vancomycin works by binding to D-ala-D-ala, but bacteria can change this sequence, preventing binding of vancomycin
