overview of antibiotics and antibiotic resistance

Question 1

how are antibiotics classified based on their acivity?

Answer 1

as bacteriostatic or bactericidal

Question 2

what is the definition of bacteriostatic?

Answer 2

a biological or chemical agent that stop bacteria from replicating, but does not kill them

Question 3

what is the definition of bactericidal?

Answer 3

a biological or chemical agent that kills bacteria

Question 4

how can bacteria be classified based on their spectrum of action?

Answer 4

as broad spectrum or narrow spectrum

Question 5

what does broad spectrum mean?

Answer 5

an antibiotic that is effective against both gram positive and gram negative bacteria

Question 6

what does narrow spectrum mean?

Answer 6

an antibiotic which is effective against a limited species of bacteria

Question 7

what parts of the bacterial cell do antibiotics target?

Answer 7

cell wall 
cytoplasmic membrane 
protein synthesis 
nucleic acid 
general enzymes

Question 8

which type of antibiotics are cell wall synthesis inhibitors?

Answer 8

beta lactam antibiotics

Question 9

how do beta lactam antibiotics work?

Answer 9

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

Question 10

what are transpeptidases also known as?

Answer 10

penicillin binding proteins

Question 11

which type of bacteria are beta lactams most effective against and why?

Answer 11

gram positive

due to large amount of peptidoglycan in the cell wall

Question 12

how do antibiotics disrupt the cell membrane?

Answer 12

some have amphipathic qualities so get incorporated into the membrane by binding to lipopolysaccharide layer

Question 13

what effect does the disruption of the cell membrane by antibiotics have on the bacterial cell?

Answer 13

affects permeability and causes cell components to leak out of the cell

Question 14

what type of bacteria are cell membrane disrupting antibiotics active against?

Answer 14

gram negative

Question 15

how can antibiotics act as protein synthesis inhibitors?

Answer 15

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

Question 16

how do DNA gyrase inhibitors work?

Answer 16

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

Question 17

what type of bacteria are DNA gyrase inhibitors active against?

Answer 17

gram positive and gram negative

Question 18

how do folic acid metabolism inhibitors work?

Answer 18

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

Question 19

what bacteria are folic acid metabolism inhibitors effective against?

Answer 19

gram positive and gram negative

Question 20

what are intrinsic resistance mechanisms?

Answer 20

naturally occurring phenomenon
independent of previous antibiotic exposure
not caused by horizontal gene transfer
usually due to lack of target or low affinity

Question 21

what are acquired resistance mechanisms?

Answer 21

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

Question 22

how does an increase in antibiotic resistance come about?

Answer 22

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

Question 23

how are antibiotics tested in a lab?

Answer 23

Kirby-Bauer Disc diffusion test
broth microdilution assay
epsilometer test