antibiotics

Question 1

5 classes of antibiotics

Answer 1

Antibiotics against bacteria 
Anti-virals 
Anti-fungals 
Anti-protosoals  
Anti-nematodes

Question 2

what are most antibiotics made from

Answer 2

natural products of bacteria and fungi, chemically modified to increase their pharmacological properties and amplify the antimicrobial effect.

Question 3

principle of selective toxicity of antibiotics

Answer 3

occurs due to the differences in structure and metabolic pathways between host and pathogen .’. host unaffected pathogen destroyed

Question 4

principle of therapeutic margin of antibiotics

Answer 4

minimum effective dosage that will inhibit or kill the bacteria.
cannot be too high bc will then affect the host cells

Question 5

what is the theraoeutic margin

Answer 5

difference between therpeutic dosage and toxic dosage

Question 6

what is microbial antagonism

Answer 6

normal flora of the body antagonising the survival of pathogenic bacteria by competing for nutrients and space

Question 7

effect of antibiotics on microbial antagonism

Answer 7

antibiotics cannot distinguish between bacteria .’. kill off normal flora and the pathogen. .’. allows overgrowth of pathogenic bacteria .’. opportunistic infection

Question 8

symptoms of overgrowth of pathogenic bacteria

Answer 8

ulceration

severe diarrhoea

Question 9

classes of bacteria based on their type of action

Answer 9

bactericidal

bacteriostatic

Question 10

what do bacteriostatic antibiotics do

Answer 10

imit the growth of bacteria by interfering with bacterial protein production, DNA replication, or other aspects of bacterial cellular metabolism.
work w/ immune system to remove the microorganisms from the body.

Question 11

what are bactericidal antibiotics

Answer 11

kill bacteria by slowing growth/reproduction of pathogen. inhibit cell wall synthesis: the Beta-lactam antibiotics (penicillin derivatives (penams), cephalosporins (cephems), monobactams, and carbapenems) and vancomycin.

Question 12

what are broad spectrum antibiotics

Answer 12

effective against many different types of bacteria e.g. cefotaxime

Question 13

what are narrow spectrum antibiotics

Answer 13

effective only against a very few types of bacteria e.g. Penicillin G

Question 14

when do we use broad spectrum antibiotics

Answer 14

emergency situations

when we don’t know exact pathogen we may use broad-spectrum antibiotics until we know the pathogen

Question 15

role of flagella on bacteria

Answer 15

enable mobility

Question 16

role of pillion bacteria

Answer 16

allow adhesion

Question 17

targets of bacteriostatic bacteria

Answer 17

inhibit: cell wall synthesis, protein synthesis, DNA gyrate, mRNA formation, antifolates

Question 18

what do dan gyrate inhibitors do

Answer 18

DNA gyrase unwinds the bacterial DNA to allow its replication, if it is inhibited the bacteria cannot replicate its DNA and divide)

Question 19

what do poymixins do

Answer 19

Act at the bacterial cell membrane, makes it more toxic towards human cells as our membranes are very similar to bacteria

Question 20

what do antifolates do

Answer 20

inhibit the ability of the bacteria to form THFA (tetrahydrofolic acid) required to make DNA precursors.

Question 21

characteristics of gram +ve bacteria

Answer 21

cell membrane encloses cytoplasm. outside the cell membrane we have large peptidoglycan cell wall.

Question 22

characteristics of cell wall in gram

Answer 22

synthesised by enzymes released grin the cell membrane.

cell wall is porous so can give b-lactam antibiotics will ps through cell wall and affect the cell membrane

Question 23

characteristics of gram -ve bacteria

Answer 23

cell membrane encloses cytoplasm. outside the cell membrane we have thin peptidoglycan cell wall, and surrounding this is an impermeable lipopolysaccharide layer. can only enter cell through porins

Question 24

why are gram -ve bacteria more resistant to antibiotics

Answer 24

have impermeable lipopolysaccharide layer .’. things can only get through via porins .’. difficult to get to periplasmic space (to inhibit peptidoglycan synthesis) or into cytoplasm (to inhibit protein synthesis

Question 25

how is peptidoglycan synthesised

Answer 25

in cytoplasm - precursor dimer made (NAG & NAM joint by UDP). D-ala added onto terminal ends. precursors then transported to space between cell membrane and wall where chain is built up. vancomycin bind to D-ala (imp to allow peptide cross linkage between carbohydrate chains) transpeptidase and carboxypeptidase then cleave one D-ala and make cross links chains.

Question 26

mechanism of penicillins and b-lactams

Answer 26

inhibit transpeptidase and carboxypeptidase .’. stop bacteria from forming cross links between the chains .’. bacteria cannot make cell wall and lyses

Question 27

how do b-lactams get into gram +ve bacteria

Answer 27

diffuse through porous cell wall

Question 28

how do b-lactams get into gram -ve bacteria

Answer 28

impermeable lipopolysaccharide membrane .’. cannot diffuse in. b-lactam has to go through the porins in impermeable layer into periplasmic layer and then moves through to bind to PBP in cell membrane

Question 29

what are PBP

Answer 29

penicillin binding proteins e.g. transpeptidase and carboxypeptidase

Question 30

mechanism of b-lactam in game -ve

Answer 30

b-lactam has to go through the porins in impermeable layer into periplasmic layer and then moves through to bind to PBP in cell membrane .’. cell wall cannot ve cross linked properly eptidoglycan subunits build up.’. autolytic enzymes induced

Question 31

how do we treat bacterial infection

Answer 31

1 - antibiotic
2 - surgery (e.g. draining abscess)
3 - immunological (e.g. antitoxin)

Question 32

why do we use antibiotics before surgery

Answer 32

used to prevent the person getting infected with organisms at the wound site

Question 33

what do we need to consider when deciding the antiobiotic we prescribe

Answer 33

Type of bacteria, Sensitivity of that bacteria, Route of administration, The clinical condition, The spectrum of activity, Level of toxicity, Can they excrete the drug

Question 34

why may antibiotic therapy not work

drug issues

Answer 34

Inappropriate drug used, Improper route of administration, Poor tissue penetration e.g. endocarditis, Inadequate dose (not reaching MIC)

Question 35

why may antibiotic therapy not work

host issues

Answer 35

Immuocompromised host, Poor circulation or damaged tissue, Unusual site for a pathogen

Question 36

why may antibiotic therapy not work

bacteria issues

Answer 36

• > Natural or acquired resistance
• > Dual infections
• > biofilms (e.g. in endocarditis)