Antibiotics and resistance

Question 1

What is the purpose of an antibiotic?

Answer 1

To target enzymes and structures that are not present in humans for selective killing of the bacteria.

Question 2

Which type of antibiotic targets the cell wall?

Answer 2

Beta lactams e.g. penicillin, cephalosporins, carbapenems, monobactams

Question 3

Which type of antibiotic targets ribosomes?

Answer 3

Tetracyclines and aminoglycosides - inferfere with protein synthesis

Question 4

Which type of antibiotic targets DNA gyrase?

Answer 4

Ciprofloxacin - Prevents replication

Question 5

Which type of antibiotic targets folic acid synthesis?

Answer 5

Sulphonamides and trimethoprim - Bacteria cannot use exogenous sources of folic acid.

Question 6

How does sulphonamide work?

Answer 6

A competitive inhibitor of para-aminobenzoic acid in the folic acid synthesis pathway, to inhibit gram +ve growth.

Question 7

What is antimicrobial resistance?

Answer 7

Lack of effect on a previously susceptible pathogen.

Question 8

How is resistance transferred through different species or between the same species of bacteria?

Answer 8

Conjugation through sex pilli.

Question 9

How is resistance measured?

Answer 9

Consecutively double the concentration of antibiotic within a broth of bacteria. The first tube that fails to show growth is the MINIMUM INHIBITORY CONC of antibiotic for that strain. Can also be done using the zone of inhibition in a petri dish.

Question 10

What enzyme is secreted by Staphylococus aureus to create resistance?

Answer 10

Secretes beta-lactamase needed to break down the beta-lactam ring. The ring is required for penicillin activity.

Question 11

What is the target of penicillin?

Answer 11

A beta lactam that binds to peptidase to inhibit the enzymes that form the crosslinks in peptidoglycan polymers of the cell wall.

Question 12

Which beta lactams were created to overcome this resistance?

Answer 12

Cleaving and adding of new sides chains to the 6-aminopenicillanic acid produced:
Cloxacillin, carbenicillin, ampicillin/amoxicillin.
All can target both gram +ve and -ve.

Question 13

Why is methicillin no longer used?

Answer 13

Caused sodium overload

Question 14

What resistance has MRSA developed?

Answer 14

Methicillin resistant Staph A has produced penicillin binding protein 2A which is a beta lactam target enzyme. Methicillin, penicillin, flucloaxcillin are all ineffective against this new enzyme as it is not targeted.

Question 15

How is MRSA controlled?

Answer 15

Through infection control - Screening, decolonisation and isolation

Question 16

What resistance did Ecoli originally develop?

Answer 16

Resistant to ampicillin due to the production of beta lactamase TEM. TEM is transferable through plasmids.

Question 17

What antibiotics were developed against this first resistance and how were they overcome?

Answer 17

Created extended spectrum cephalosporins but the bacteria developed resistance through ESB lactamases and cephalosporinase CTX-M allowed the resistance to spread.

Question 18

Which type of antibiotic is effective against Ecoli?

Answer 18

Carbapenems as ESB lactamases are ineffective against them

Question 19

When are carbapenems used?

Answer 19

As a last line for most bacteria

Question 20

What has led to the high levels of resistance?

Answer 20

Use of antimicrobials in food production and medicine. Megacities, poor public health has helped gram -ve bacteria resistance to spread.

Question 21

How can the risk of resistance be reduced?

Answer 21

Reduce use of antibiotics.
Use a broad spectrum antibiotic originally but change to narrow spectrum once the strain is identified.
Use carbapenems against gram -ve.
Reduce hospital acquired infections by screening non-UK Pts for carbapenamase genes and use isolation.
Infection control and hygiene.

Question 22

What are the two most common hospital acquired infections?

Answer 22

C.difficle - imbalance of gut flora causing toxic megacolon

Norovirus - severe vomiting and diarrhoea

Question 23

What is the main consequence of antibiotics?

Answer 23

Can cause renal impairment and become toxic

Question 24

In what ways are antibiotics being used inappropriately?

Answer 24

Overprescribing
Extended or uncompleted courses
Use on viral infections
Developing countries do not require a prescription to access antibiotics