Antibiotic Action and Resistance

Question 1

What is an antibiotic?

Answer 1

A substance produced by a micro-organism (or a similar substance produced wholly or partly by chemical synthesis) which at low concentrations kill or inhibit the growth of other micro-organisms”

• Antibacterial drugs
• Antifungal drugs
• Antiviral drugs

Question 2

What is antibiotic resistance?

Answer 2

An organism (bacterium) is resistant when it will not respond to an attainable level of a drug (antibiotic) in living tissue

Question 3

What are the different mechanisms by which antibiotics work?

Answer 3

• Weaken bacterial cell wall
• Disrupt cell membrane
• Disrupt cell division/DNA replication
• Disrupt synthesis of proteins by RNA
• Disrupt other metabolic processes e.g. folic acid production

Question 4

Which anti-microbial agents interfere with cell wall synthesis?

Answer 4

b-lactams: Penecillins, cephalosporins, carbapenems, monobactams

Glycopeptides: vancomycin, teicoplanin

Question 5

Which anti-microbial agents inhibit protein synthesis?

Answer 5

By binding to the 50s ribosomal subunit: macrolides, chloramphenicol, clindamycin, quinupristin-dalfopristin, linezolid

By binding to the 30s ribosomal subunit: aminoglycosides, tetracyclines

By binding to bacterial isoleucyl-tRNA synthetase: mupirocin

Question 6

Which anti-microbial agents interfere with nucleic acid synthesis?

Answer 6

Inhibit DNA synthesis - fluoroquinolones

Inhibit RNA synthesis - rifampin

Question 7

Which anti-microbial agents inhibit metabolic pathways?

Answer 7

Sulfonamides

Folic acid analogues

Question 8

Which anti-microbial agents disrupt bacterial membrane structure?

Answer 8

Polymyxins

Daptomycin

Question 9

What is the Minimum Inhibitory Concentration (MICs) for Methicillin?

Answer 9

4 to 8 mcg/mL considered to represent borderline or low level resistance

Question 10

What are the causes of antibiotic resistance?

Answer 10

Inappropriate use of antibiotics
– Worldwide overuse of antibiotic
Extensive use in upper respiratory infections
– Incomplete or incorrect therapeutic regimens
– Availability of antibiotics without prescriptions
Failure of hospital infection control policies
Increased opportunities for dissemination of antibioticresistant bacteria both within and outside the hospital setting
– Global dissemination of particular strains
Widespread use of antibiotics as a “growth enhancer” in agriculture

Question 11

Describe the scale of the problem of antibiotic resistance

Answer 11

Bacterial multidrug-resistant mortality rate:
25,000 patients die annually in the EU
>63,000 patients in United States die every year from hospital-acquired infections

Estimated economic costs due to infections by multidrug-resistant bacteria in EU (extra healthcare costs and productivity losses) €1.5 billion each year

Cost of treating hospital-acquired infections from just six antibiotic-resistant bacterial species in US estimated to be at least $1.87 billion

Question 12

Describe the scale of the problem of antibiotic resistance within Europe

Answer 12

Across Europe, an estimated 25,000 people die each year as a result of hospital infections caused by the following 5 resistant bacteria:
• Escherichia coli
• Klebsiella pneumoniae
• Enterococcus faecium
• Pseudomonas aeruginosa
• Methicillin-resistant Staphylococcus aureus (MRSA)

This adds over £1 billion to hospital treatment and societal costs.

Question 13

How much did the rate of Escherichia coli and Klebsiella pneumoniae bloodstream infections increase in England between 2010 and 2014?

Answer 13

E. coli - 15.6%

K. pneumoniae - 20.8%

Question 14

What were the 3 most frequently prescribed groups of antibiotics in England 2014?

Answer 14

Penicillins - 45%
Tetracyclines - 22%
Macrolides - 15%

Question 15

How many people in hospital in England are on an antibiotic at any one time?

Answer 15

1 in 3

Question 16

How many individuals in England take at least one course of antibiotics each year?

Answer 16

1 in 3

Question 17

What are the consequences of antimicrobial

resistant bacteria?

Answer 17

• Increased number of hospitalizations
• Increased length of hospitalization
• Increased morbidity and mortality
– Emergence of strains totally resistant to all available antimicrobials
• Choice of more expensive or more toxic therapeutic alternatives

Question 18

What could be the consequences of a global failure to address the problem of antibiotic resistance?

Answer 18

10 million deaths by 2050 costing £66 trillion

Question 19

What are the different types of antibiotic resistance?

Answer 19

Inherent / intrinsic

Acquired

1) Chromosomal
2) Transferable

Question 20

Describe inherent/intrinsic antibiotic resistance

Answer 20

All strains of a given species are resistant to a particular antibiotic, to which they have not had direct exposure

Question 21

Why are some species inherently resistant to a particular antibiotics?

Answer 21

Inability to permeate cell envelope or lack of target

Question 22

Give examples of inherent antibiotic resistance

Answer 22

Streptococci - aminoglycosides

Gram negatives - vancomycin

Question 23

Describe Chromosomal resistance

Answer 23

Vertical gene transfer

Antibiotic pressure causes mutation from sensitive to resistant strain

Question 24

Give examples of chromosomal resistance

Answer 24

Mycobacterium tuberculosis - streptomycin, rifampicin

Gram negatives – cephalosporins

Question 25

What are the different mechanism for transferable resistance (horizontal gene transfer)?

Answer 25

Transduction Conjugation Transformation

Question 26

What is conjugation?

Answer 26

Plasmid mediated transfer of single or multiple resistance genes Most important clinically – spreads easily strain to strain Plasmids are extra chromosomal DNA that carry resistance (R) factors Plasmids are common and wide spread and transfer easily among bacteria

Question 27

What is transduction?

Answer 27

Bacteriophage (virus) mediated transfer of genes

Question 28

What is Transformation?

Answer 28

Acquisition of free DNA (resistance genes) by naturally transformable species

Question 29

What are the various mechanisms for antimicrobial resistance?

Answer 29

a) Decreased accumulation of antibiotic – Permeability barriers - outer membrane Gram negatives - penicillins – Porin mutation – Antibiotic efflux pumps -tetracyclines, macrolides b) Enzymatic antibiotic inactivation or modification – β-lactamases c) Alteration of the drug target – methicillin, vancomycin, macrolides

Question 30

What are bacterial efflux pumps?

Answer 30

Bacterial efflux pumps are common within bacteria • Efflux pumps are proteinaceous transporters localised in the cytoplasmic membrane (and outer membrane) • Active transporters therefore require a source of energy • Bacterial efflux pumps classified into five major “superfamilies” based on: – amino acid sequence – energy source used to export antimicrobial

Question 31

What are the 5 major "superfamilies" of bacterial efflux pumps?

Answer 31

* Multidrug and toxic compound extrusion family (MATE) * Major facilitator superfamily (MFS) * Small multidrug resistance family (SMR) * Resistance nodulation cell division superfamily (RND) * ATP-binding cassette superfamily (ABC)

Question 32

Describe the enzymatic antibiotic inactivation or | modification of b-lactams

Answer 32

Amide bond of the β-lactam ring hydrolysed by β-lactamase

Question 33

How does alteration of the drug target for macrolides cause antibiotic resistance?

Answer 33

Inhibition of Protein Synthesis Erythromycin (macrolide) binds to the ribosome causing - dissociation of tRNA which inhibits the elongation of the protein chain - bacteriostatic action Erythromycin resistance is chromosomally mediated, related to an alteration of the target site (the ribosome) Alteration (mutation) of one of two adenine residues in the 23S rRNA at the antibiotic-binding site

Question 34

How do fluoroquinolones work as antibiotics?

Answer 34

Fluoroquinolones block genetic replication by interfering with synthesis of DNA Bind to enzymes and inhibit DNA replication - DNA gyrase ( topoisomerase II ) – DNA supercoiling - topoisomerase IV – required for strand separation during replication

Question 35

How does resistance to fluoroquinolones occur?

Answer 35

• Mutation to: DNA gyrase (gyrA) (occasionally) topoisomerase IV (parC) • Resistance – mutation of genes responsible for enzyme production cause conformational change by incorporating hydrophobic sub-units • This reduces affinity for fluoroquinolones

Question 36

How can antibiotic resistance be controlled?

Answer 36

Reduce exposure to antibiotics | Develop new antibiotics