Ch 20 Antimicrobial Drugs Flashcards
define chemotherapy
use of drugs to treat a disease (ex: antibiotics)
define antibiotics
subs. produced by a mircobe that, in small amounts, inhibits another microbe
where antibiotics come from
chemicals evolved by microbes in an attempt to inhibit others around them
define selective toxicity
killing microbes w/o damaging host (criteria of human antibiotics)
difference between broad spectrum and narrow spectrum antibiotics
broad spectrum- Ab’s that affect a wide range of bacteria (gram-pos and neg)
narrow- Ab’s w specific range and only effect small # of bacteria types
what is a superinfection
infection that occurs as a result of overgrowth of microbes after a broad spectrum Ab reduces the number of normal microbiota (destroys a microbes competitor)
Also applies to growth of pathogen that has developed resistance
antibiotics work on fast or slow growing bacteria
fast (ex: clostridium difficile is slow growing, survives while others die, can overgrow)
5 major action modes of Antimicrobial drugs
Inhibition of cell wall synth., protein synth., nucleic acid replication and transcription ;
injury to PM, inhibition of essential metabolite synthesis
how antimicrobials inhibit cell wall synthesis
inhibits formation of peptide cross bridges-> cell “falls apart”
how chloramphenicol inhibits protein synthesis
binds to 50S portion of ribosome, inibits formation of peptide bond-> no polypeptide strands made and no proteins made
how tetracyclines work to inhibit protein synthesis
interfere w attachment of tRNA to mRNA (no protein synthesized)
how streptomycin works to inhibit protein synthesis
changes the shape of 30S ribosome portion-> incorrect reading of mRNA-> non-functioning proteins produced
why inhibition of nucleic acid synthesis is problematic
can inhibit host DNA replication as well as bacterial
why inhibition of protein synthesis can be problematic
bacterial and mitochondrial ribosomes same size, side effects bc low functioning mitochondria
how certain antibiotics work to injure the PM
some block fatty acid synthesis (prevent formation of bilayer)
which antibiotic major action mode is most effective against gram neg bacteria
injury to PM
example of an antibiotic that works by inhibiting an essential metabolite
solfanilamide- acts as competitive inhibitor of metabolic pathway that uses PABA to make folic acid (critical for nucleic acid synthesis)
what is MIC
minimal inhibitory concentration; lowest antibiotic concentration that prevents visible bacterial growth
tests to determine MIC
gradient diffusion method “E test” (gradient strip of antibiotic agent) or disk diffusion method (of each paper disk same antibiotic at diff concentrations)
Or a microdillution/ microtiter- growth of microbes w/in Wells with decreasing concentration of drug
while a variety of mutations can lead to antibiotic resistance abilities, what other method of developing these abilities is more likley
resistant genes already on plasmids or transposons are present in a population of bacteria, transferred
examples of missuse of antibiotics
taking antibiotics that are outdated or weakened, not yours, for inappropriate conditions like the common cold, or antibioitcs in animal feed or not completing antibiotic regimen
how bacteria become antibiotic resistent by blocking entry of antibiotic
change cell wall, doesnt allow in
how bacteria use enzymes to become antibiotic resistent
develope, evolve, or select for enzymes that can inactivate antibiotics
how bacteria utilize target molecules to become antibiotic resistant
many antibodies work by targeting a specific mlcl, bacteria may alter it so they wont be effective
