antimicrobial therapy Flashcards
what is a chemotherapeutic agent
a chemical agent that is used internally to kill/inhibit the growth of microbes
what type of agent is a chemotherapeutic agent
chemical
what trait should a chemotherapeutic agent have to be successful
selective toxicity
define selective toxicity
ability to kill/inhibit growth of the microbe without damaging the host
how can the degree of selective toxicity be expressed (2 things)
therapeutic dose
toxic dose
what is the therapeutic index
toxic dose divided by therapeutic dose
do we want a low or a high therapeutic index? explain
high; means we have a large toxic dose so we can give the drug at a low concentration
in regards to TI, when might side effects occur
when there is a low TI
list some side effects from a chemotherapeutic agent
allergic responses, toxicity, renal failure
list some targets of prokaryotes (microbes) that can be used when we’re looking for selective toxicity (ie what can we target the drug to that wont be in the host)
capsule, cell wall (peptidoglycan), 70S ribosomes
define narrow spectrum
the agent is effective against a small number of pathogens
define broad spectrum
the agent is effective against a large number of pathogens
what might you call a drug that works against fungi
antifungal
what might you call a drug that inhibits the growth of fungi
fungistatic
T or F: the chemo agent isn’t useful if it only inhibits the growth of a microbe and not kills it
false; it is still useful bc after growth is inhibited then the immune system can kick in to kill it
how are antibiotics made
synthesized by microbes
example of an antibiotic
penicillin G
how are synthetics made
via chemical procedures
what are semisynthetics
agents that are combinations of synthetics and antibiotics (both synthesized by microbes and chemical procedures)
example of a semisynthetic
ampicillin
what does MIC stand for
minimum inhibitory concentration
what is the MIC
lowest conc. of a drug that inhibits the growth of the pathogen
what does MLC stand for
minimum lethal concentration
what is the MLC
lowest conc. of the drug that kills the pathogen
T or F: different species will have different susceptibilities to chemotherapeutic agents
true
T or F: susceptibility may change with time
true
list three susceptibility tests that may be done
dilution susceptibility
disk diffusion (Kirby-Bauer)
E test
what is the dilution susceptibility test used for
determining the MIC and MLC
procedure of the dilution susceptibility test
dilutions of the drug are made in Meuller-Hinton broth or agar, each tube is inoculated with a standard amount of bacteria, after 16-20 hours incubation the presence of growth is noted
what type of broth/agar is used in the dilution susceptibility test
Meuller-Hinton
procedure of disk diffusion test (Kirby-Bauer)
inoculate on agar plate with a standardized amount of the microbe. A filter disk impregnated with a known conc of the agent is placed on the surface + incubated. The antibiotic will diffuse into the agar. The diameter of the no-growth zone is measured
procedure of the E test
uses a plastic coated strip that contains a gradient of antibiotic concentrations + the MIC is read from the scale printed on the strip
list the five major modes of action of antibacterial drugs
inhibition of cell wall synthesis, inhibition of protein synthesis, injury to PM, inhibition of nucleic acid synthesis, inhibition of essential metabolites
how do agents inhibit cell wall synthesis
prevent NAM subunit crosslinking in peptidoglycan layer
do drugs that inhibit cell wall synthesis have a high or low TI
high TI
how do agents inhibit protein synthesis
they bind with prokaryotic ribosomes (50S or 30 S subunit) and inhibit translation
do agents that inhibit protein synthesis have a high or low TI
high TI
how do agents cause injury to the PM
they change the permeability by incorporating themselves into it, thereby damaging its integrity, resulting in cell leakage
how do agents inhibit nucleic acid synthesis
they interfere with DNA replication and transcription processes
how do agents inhibit essential metabolites
they interfere with metabolic pathways by competitively inhibiting the use of the normal substrate by the enzyme
what do sulfa drugs work against
microbes that make their own folate
why do sulfa drugs work against microbes that make their own folate
humans get folate from our diet, so the sulfa drugs will only target the pathogen and not the host
