Antibiotics

Question 1

what are antibiotics

Answer 1

against life

anti-bacterials

Question 2

where do antibiotics come from?

Answer 2

metabolic products of bacteria or fungi .

Modern synthesised by fermentation then modification

Question 3

phases of bacterial growth

Answer 3

lag phase
log - exponential phase
stationary phase
death phase

Question 4

why does bacterial growth halt?

Answer 4

no more space or ran out of nutrients

Question 5

what does bacteria need to grow?

Answer 5

nutrient

appropriate physical and chemical environment

Question 6

what are the features of a good antibiotic?

Answer 6

effective
safe
slow emergence of resistance
long half-life
good tissue distribution
oral bioavailability
cheap
Ideal antimicrobial agents severely damage microorganisms but have much less effect on human metabolism

Question 7

what are the 2 types of antibiotics

Answer 7

bacteriostatic agent

bactericidal agent

Question 8

Bacteriostatic agent

Answer 8

halts bacterial growth, levels out population

Question 9

bactericidal agent

Answer 9

kills bacteria, reduces number of bacteria present

Question 10

what are the different modes of action?

Answer 10

inhibition of cell wall synthesis 
metabolic antagonism 
interference with nucleic acid synthesis
inhibition of protein synthesis
action on membrane

Question 11

cell wall synthesis

Answer 11

peptidoglycan present in bacterial cell walls
long polysaccharide chains and short peptide side chains
for bacterial growth - bonds must be cut
if transpeptidation is inhibited - bacterial cells lyse
prevents formation of cross-links between tetrapeptide chains

Question 12

cell wall synthesis inhibitors

Answer 12

beta lactam antibiotics inhibit transpeptidation

glyopeptide antibiotics inhibit cross linking

Question 13

examples of beta lactam antibiotics

Answer 13

penicillins
cephalosporins
carbapenams

Question 14

example of glycopeptide antibiotic

Answer 14

vancomycin

Question 15

metabolic antagonism

Answer 15

interrupt bacterial metabolic pathways
block enzyme activity by various mechanisms
Interrupts the folic acid pathway by inhibiting intermediates within the pathway .
e.g. trimethoprim

Question 16

what is folic acid needed for?

Answer 16

DNA synthesis

Question 17

Interference with nucleic acid synthesis

Answer 17

bacterial DNA stored as supercoiled
uncoiled for replication and transcription
DNA gyrase assists with unwinding .

Question 18

selective toxicity

Answer 18

ideal antimicrobial agents severely damage microorganisms but have much less effect on human metabolism

Question 19

examples of antibiotics that interfere with nucleic acid synthesis

Answer 19

Quinolones - ciprofloxacin which inhibits DNA gyrase

Rifamycins - rifampicin which inhibits RNA polymerase

Question 20

what is metronidazole?

Answer 20

pro drug
converted to toxic metabolite
inhibits DNA synthesis and breaks down existing DNA

Question 21

inhibition of protein synthesis

Answer 21

bacterial ribosomes differ from human ones

Question 22

examples of antibiotics that inhibit protein synthesis

Answer 22

macrolides
aminoglycosides
tetracyclines

Question 23

what do macrolides do?

Answer 23

target 50S subunit

e.g. clarithromycin

Question 24

what do aminoglycosides do?

Answer 24

target both subunits
e.g. gentamicin
they are unlike other protein synthesis inhibitors bactericidal

Question 25

what do tetracyclines do?

Answer 25

target 30S subunit

e.g. doxycycline

Question 26

antibiotics that act on cell membrane

Answer 26

reserved only for gram negative infections that are resistant to other antibacterials
need to monitor neurotoxicity and nephrotoxicity
rarely use in bacteria but are very important as antifungal drugs

Question 27

examples of antibiotics that target the cell membrane

Answer 27

colistimethate sodium

polymyxin B

Question 28

effective use of antibiotics

Answer 28

knowledge of likely infecting organism
likely bacterial susceptibility
site of infection
spectrum of action
absorption and distribution of antibiotics

Question 29

pharmacological considerations of antibiotics

Answer 29

target site of infection affects route of administration
knowledge of route of excretion
modify dose according to patient, specifically renal or liver disease

Question 30

antibiotic resistance

Answer 30

some microorganisms are naturally resistant to some antibiotics whilst others acquire resistance especially when under selective pressure

Question 31

natural resistance e.g.

Answer 31

penicillin cannot penetrate cell wall of gram -ve bacteria

Question 32

acquired resistance e.g.

Answer 32

bacteria produce beta lactamase so beta lactams are no longer effective in some bacteria

Question 33

mechanisms by which bacteria develop resistance

Answer 33

spontaneous mutation
conjugation
transduction
transformation

Question 34

what is conjugation?

Answer 34

sharing of DNA between bacteria

Question 35

what is transduction

Answer 35

genetic recombination in bacteria in which genes from a host cell are incorporated into the genome of a bacterial virus - bacteriophage and then carried to another host cell when the bacterophage initiates another cycle of infection

Question 36

what is transformation?

Answer 36

incorporates dead bacterial DNA into the genome of a living bacteria

Question 37

mechanisms of resistanc

Answer 37

altered up take
increased exit
drug inactivation
altered target site
altered metabolic pathways

Question 38

what happens in increased exit?

Answer 38

the bacteria removes the antibiotic from the cell

Question 39

what happens in altered target site?

Answer 39

mutation of target site

Question 40

what happens in altered metabolic pathways?

Answer 40

bypasses target action of drug