Antibiotics

Question 1

What are antimicrobials

Answer 1

Antimicrobials are substances that kill or inhibit the growth of microorganisms

Question 2

What are antibiotics

Answer 2

• Substances produced by living organisms with activity against bacteria
• Many of our current drugs are not true antibiotics but are either synthetic or semi-synthetic
• Chemically modified to improve pharmacological and antimicrobial properties

Question 3

Briefly describe how the first antibiotic was discovered

Answer 3

• Alexander Flemming was growing a culture of staphylococcus aureus which was contaminated with penicillium notatum
• The penicillium produced a substance that created a zone of inhibition on the culture

Question 4

What does selective toxicity mean

Answer 4

• Only targets specific cells due to the differences between the pathogen and the host

Question 5

What does therapeutic margin mean

Answer 5

• The difference between the therapeutic dose and the toxic dose
• The greater the margin the safer the drug

Question 6

What is the effect on normal microbiota when using antibiotics

Answer 6

• The use of broad-spectrum antibiotics can lead to dybiosis
• Loss of flora can lead to bacterial or pathogen overgrowth

Question 7

How does antibiotics work along side immunity

Answer 7

• Antibiotics work alongside natural immunity to clear bacteria.
• When patients are immunosuppressed it affects the types of antibiotics used

Question 8

How are antibiotics classified

Answer 8

• Type of activity
• Structure
• Target site for activity

Question 9

What types of activities can antibiotics be

Answer 9

• Bactericidal
• Bacteriostatic

Question 10

What is the function of bactericidal antibiotics

Answer 10

• Kill bacteria
• Used when the host defence mechanisms are impaired
• Required in endocarditis, kidney infection diseases

Question 11

What is the function of bacteriostatic antibiotics

Answer 11

• Inhibit bacteria
• Used when the host defences mechanisms are intact
• Used in many infectious diseases

Question 12

How are antibiotics classified on their spectrum of activity

Answer 12

• Broad spectrum antibiotics
• Narrow spectrum antibiotics

Question 13

Describe beta-lactams as antibiotics

Answer 13

• Basic penicillins
• Active against streptococci, pneumococci, meningococci, treopnemes
• Most strains of Staphylococcus aureus are resistant.

Question 14

Describe Anti-staphylococcal penicillins
e.g. flucloxacillin

Answer 14

• narrow spectrum, Gram-positive, beta-lactamase resistant, less potent than PenG

Question 15

Describe broader spectrum penicillins e.g. ampicillin

Answer 15

Spectrum of activity is similar to basic penicillins but also includes some Gram-negative organisms and also enterococci

Question 16

Describe Anti-pseudomonal penicillins e.g. piperacillin

Answer 16

extended spectrum beta-lactam antibiotic also gram positive and negative anaerobes

Question 17

Describe Beta-lactam/beta-lactamase inhibitor combinations
e.g. co-amoxiclav (Augmentin)

Answer 17

Spectrum like amoxicillin plus activity against some Gram-negatives and Staph aureus

Question 18

List some targets of activity for antibiotics

Answer 18

• Cell wall synthesis
• DNA Gyrase
• RNA elongation
• DNA-directed RNA polymerase
• Protein synthesis inhibitors 50S, 30S and tRNA
• Cytoplasmic membrane structure
• Folic acid metabolism

Question 19

Briefly describe how cell wall inhibitors work

Answer 19

• Peptidoglycan synthesis involves enzymes called penicillin-binding proteins (PBPs)(Transpeptidases)
• When new peptidoglycan units are added to a growing cell wall, the peptide side chain on one subunit must be linked to peptide side chain on another (Transpeptidation)
• Structure of penicillins resembles the two amino acids at the end of the side chain – terminal D alanyl-D-alanine
• The transpeptidation enzyme binds penicillin instead of its true substrate due to this structural similarity, thereby blocking the transpeptidation reaction that forms the peptidoglycan cross-links

Question 20

How does beta-lactams work on gram negative bacteria

Answer 20

• Beta-lactams travel through porins present on outer membrane and bind transpeptidases
• This stops production of the peptidoglycan layer
• Activates autolytic enzyme mechanisms

Question 21

How does folic acid synthesis inhibitors work

Answer 21

• Sulphonamides acts as competitive inhibitors for dihydropteroate synthetase in the production of folic acid
• Trimethoprim inhibits dihydrofolate reductase
• Conditions are synergistic and bactericidal

Question 22

Describe how protein synthesis inhibitors work

Answer 22

• Either bind to the 30S or 50S subunit and blocks formation of peptide chain

Question 23

When do we use antibiotics

Answer 23

• Treatment for bacterial infections
• Prophylaxis - Prevent infections
• Inappropriate use - viral sore throats

Question 24

What route of administrations are used

Answer 24

• Oral
• IV
• Injection
• Topical

Question 25

Why are antibiotic combinations used

Answer 25

- Before an organism is identified in life-threatening infections - Polymicrobial infections - Less toxic doses of an individual drug possible - Synergy between more than one antibiotic - reduce antibiotic resistance

Question 26

What is meant by MIC dose

Answer 26

- The minimum does required to cause inhibition - A therapeutic dose will be higher than the MIC

Question 27

What is antibiotic susceptibility testing

Answer 27

- Test which antibiotics work against an infection and at what concentration