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level: Case 4

Questions and Answers List

level questions: Case 4

QuestionAnswer
what are the different classes of antibiotics?beta lacatams (target cell wall) penicillins cephalosporins, cephamycin carbapenems monobactams target protein synthesis aminoglycosides macrolides target nucleic acid synthesis quinolones antimetabolites
what is the differences between penicillins and cephalosporins?the beta-lactam ring of cephalosporins is fused with a dihydrothiazine ring cephalosporins have a wider spectrum than penicillins
how do quinolones work?they target nucleic acid synthesis by inhibiting topoisomerase type II for gram-negative bacteria and topoisomerase type IV for gram-positive bacteria. this prevents DNA replication, recombination and repair.
how do antimetabolites work?they target nucleic acid synthesis by competing with the enzyme PABA, which is needed for the production of folic acid. because of this inhibition purines and pyrimidines cannot be made
how do aminoglycosides work?they target protein synthesis by binding to the 30S subunit of the ribosome. this creates the wrong proteins causing cell death
how do macrolides work?they target protein synthesis by binding to the 23S ribosomal RNA of the 50S ribosome. this blocks peptide elongation. this is a reversible mechanism
how do the beta-lactams work?they target the cell wall synthesis by binding to the penicillin-binding proteins, which inhibits the assembly of peptidoglycan. this causes lysis and cell death
which antibiotics are bactericidal and which ones are bacteriostatic?bactericidal: aminoglycosides, beta-lactams, bacteriostatic: macrolides
what is the difference between penicillin G and V?penicillin G is unstable in gastric acid and is thus administered intravenously penicillin V is more resistant to gastric acid and is administered orally
why do penicillins work better on gram-positive than gram-negative bacteria?the gram-negative bacteria have an outer membrane that the penicillins have to cross before they can do their job. this crossing depends on if the antibiotic fits through the pores of the bacteria. the gram-positive bacteria do not have this membrane
what is the difference between cephalosporins and cephamycins?cephalosporins contain sulfer in their dihydrothiazine ring, while cephamycins have oxygen located there
what do the different spectrums tell you about cephalosporins?the narrow spectrum cephalosporins are the antibiotics that were first found and that are not that effective to a lot of bacteria. the more you move up in spectrum (expanded, broad, extended) the more active the antibiotics are to other bacteria. the antibiotics in the broad spectrum can pass the blood-brain barrier and the ones in the extended spectrum can pass the outer membrane more easily.
how is the peptidoglycan of the cell wall synthesized?1. the precursors are synthesised and activated in the cell 2. the acetylglucosamine and acetylmuramic acid are attached to bactoprenol 3. bactoprenol is transferred to the other side of the cell wall 4. peptidoglycan is extended; transpeptidases cross-link the peptidoglycan and D-carboxypeptidases remove unreacted D-alanines
what does LPS compose of and in what order? (from proximal to distal of the cell)1. lipid A 2. core polysaccharide 3. O antigen the bacteria is recognized by its O antigen
how does bacterial resistance develop for each antibiotic?beta-lactams: decreased concentration of antibiotic at the target, decreased binding to PBP, hydrolysis by beta-lactamases aminoglycosides: modification of the antibiotic, mutation of the ribosome, decreased uptake of antibiotic in the cell, increased efflux quinolones: chromosomal mutations, increased efflux, membrane permeability mutation antimetabolites: changes to the cell membrane
what are the four general mechanisms for developing resistance against antibiotics for bacteria?target modification efflux immunity (antibiotics bound to other proteins so they can't bind their target) enzyme catalyze destruction (enzyme destroys the antibiotic)
what are the four classes of beta-lactamases?class A: SHV-1, TEM-s and ESBLs class B: zinc dependent metalloenzymes class C: mainly cephalosporinases class D: mainly penicillinases
what is the function of beta-lactamases?they work against beta-lactam antibiotics by hydrolyzing them, meaning the addition of a water molecule. this causes the beta-lactam to fall apart in small pieces.
what types of ESBLs are there and how are they formed?TEM: formed by point mutation (in TEM-1 or TEM-2) SHV: formed by point mutation CTX-M: formed by horizontal gene transfer
how is bacterial resistance tested?disc diffusion test: bacteria are put on an agar plate, antibiotic is applied and discs are incubated, looked at the zone of inhibition broth dilution: bacteria is mixed with media and compared to other tubes to determine the minimum inhibitory concentration (MIC)
what is the breakpoint and minimum inhibitory concentration?breakpoint: chosen concentration of the antibiotic which defines whether the bacteria is susceptible or resistant to the antibiotic minimum inhibitory concentration: lowest concentration of the antibiotic that inhibits the growth of the bacteria bacteria is resistant when MIC is above the breakpoint bacteria is susceptible when MIC is equal to or below the breakpoint