chapter 20: antimicrobial drugs Flashcards
chemotherapy
the use of drugs to treat a disease
antimicrobial drugs
interfere with the growth of microbes within a host
antibiotic
a substance produced by a microbe that, in small amounts, inhibits another microbe
selective toxicity
the principle that a drug should be toxic to the intended target but not the host (ie a useful antibiotic should kill harmful microbes without damaging the host)
bactericidal
kill microbes directly- in many cases most desirable choice (however, may be contraindications…host range, solubility, toxicity, etc.)
bacteriostatic
prevent microbes from growing-relies on host’s immune response to finish the job and eliminate the microbes
the action of antimicrobial drugs: different ways
1) inhibition of cell wall synthesis: penicillins, cephalosporins, bacitracin, vancomycin
2) inhibition of protein synthesis
3) inhibition of nucleic acid replication and transcription
4) injury to plasma membran
5) inhibition of synthesis of essential metabolites
inhibitors of cell wall synthesis
penicillin G, ampicillin, cephalosporins, vancomycin
inhibitors of protein syntheis
chloramphenicol, streptomycin, gentamicin, erythromycin
inhibitors of nucleic acid synthesis
rifampin
competitive inhibitors of the synthesis of essential metabolites
trimethoprim-sulfamethohoxazole
action of penicillin on cell wall formation
penicillin block the peptide crosslinking step in peptidoglycan synthesis, thus preventing cross-bridge formation in growing ells, weakens cell wall; cells burst, only active on growing cells **
common structure among penicillins?
beta-lactam ring
beta-lactam antibiotics
penicillin (penicillinase-resistant penicillins, penicillins + B-lactamase inhibitors), carbapenems (substitue a C for an S, add a double bond), monobactam (single ring)
cephalosporins
first gen: narrow spectrum; act against gram-positive bacteria, second gen: extended spectrum includes gram-negative bacterian, third gen: includes pseudomonads; injected, fourth gen: oral
penicillinase
an enzyme encoded by some bacteria, often on plasmids, breaks the beta-lactam ring, rendering penicillin inactive and thus, conferring resistance to penicillin on the bacterium
augmentin
formulation of [amoxicillin + potassium clavulanate] clavulanate inhibits penicillinase (B-lactamase) thus allowing penicillin (amoxicillin) to remain intact and to work
vancomycin
glycopeptide, important “last line” against antibiotic-resistant S. aureus
chloramphenicol
binds to 50S potion and inhibits the formation of peptide bond, broad spectrum
rifamycin
inhibits RNA synthesis, antituberculosis
antibiotic resistance (4 methods)
1) blocking entry
2) inactivating enzymes
3) alteration of target molecule
4) efflux of antibiotic
what leads to antibiotic resistance
a variety of mutations
mechanisms of antibiotic resistance
1) enzymatic destruction of drug
2) prevention of penetration of drug
3) alteration od drug’s target site
4) rapid ejection of the drug
resistance genes are often on ____ or ____ that can be …..
plasmids, transposons, transferred between bacteria