overview of antibiotics and antibiotic resistance Flashcards
how are antibiotics classified based on their acivity?
as bacteriostatic or bactericidal
what is the definition of bacteriostatic?
a biological or chemical agent that stop bacteria from replicating, but does not kill them
what is the definition of bactericidal?
a biological or chemical agent that kills bacteria
how can bacteria be classified based on their spectrum of action?
as broad spectrum or narrow spectrum
what does broad spectrum mean?
an antibiotic that is effective against both gram positive and gram negative bacteria
what does narrow spectrum mean?
an antibiotic which is effective against a limited species of bacteria
what parts of the bacterial cell do antibiotics target?
cell wall cytoplasmic membrane protein synthesis nucleic acid general enzymes
which type of antibiotics are cell wall synthesis inhibitors?
beta lactam antibiotics
how do beta lactam antibiotics work?
inhibit the synthesis pf the peptidoglycan layer of the cell wall
resemble the D-ala-D-ala structure so the transpeptidases bind to its active site
what are transpeptidases also known as?
penicillin binding proteins
which type of bacteria are beta lactams most effective against and why?
gram positive
due to large amount of peptidoglycan in the cell wall
how do antibiotics disrupt the cell membrane?
some have amphipathic qualities so get incorporated into the membrane by binding to lipopolysaccharide layer
what effect does the disruption of the cell membrane by antibiotics have on the bacterial cell?
affects permeability and causes cell components to leak out of the cell
what type of bacteria are cell membrane disrupting antibiotics active against?
gram negative
how can antibiotics act as protein synthesis inhibitors?
can bind to the 30S portion and inhibit translation by causing the mRNA code to be read incorrectly
can prevent binding of tRNA to the ribosome
can bind to the 50S portion inhibiting the formation of peptide bonds
can interfere with the attachment of tRNA to to mRNA-ribosome complex
can bind to the 50S portion and prevent the movement of the ribosome along mRNA
how do DNA gyrase inhibitors work?
block DNA replication by interfering with the action of DNA gyrase
block the reaction and trap gyrase or topoisomerase IV causing DNA breakage
repair mechanisms cause lethal mutations
what type of bacteria are DNA gyrase inhibitors active against?
gram positive and gram negative
how do folic acid metabolism inhibitors work?
humans do not synthesise folic acid so it is a good selective target
block different parts of the tetrahydrofolic acid synthesis pathway
thfa is an essential enzyme cofactor which bacteria need for survival
what bacteria are folic acid metabolism inhibitors effective against?
gram positive and gram negative
what are intrinsic resistance mechanisms?
naturally occurring phenomenon
independent of previous antibiotic exposure
not caused by horizontal gene transfer
usually due to lack of target or low affinity
what are acquired resistance mechanisms?
bacteria develop mutations during replications which make them resistant
most frequent are mutations in genes encoding for the target molecules of antimicrobials
also due to horizontal gene transfer
how does an increase in antibiotic resistance come about?
when someone has an infection there is usually both drug resistant and non resistant bacteria present
antibiotics kill the non resistant organisms creating an ideal environment for drug resistant bacteria to take over
they can then become dominant and a new infection can occur
how are antibiotics tested in a lab?
Kirby-Bauer Disc diffusion test
broth microdilution assay
epsilometer test
