Antibiotics

Question 1

What is prophylactic therapy?

Answer 1

No s/sx of infection, trying to avoid it

Make the best choice of antimicrobial that will reduce the pathogen at the potential site of infection

Question 2

What is empiric therapy?

Answer 2

Clinical s/sx present

Requires knowledge of the most likely pathogens

Infection is known and/or clinically apparent (ex. most likely pathogen in a UTI is E. coli)

Make the best choice of antimicrobial that will help eradicate the pathogen at the site of infection and take host factors into account

Question 3

What is definitive therapy?

Answer 3

Site of infection usually known, bacterial susceptibilities known

The data on the pathogen(s) and susceptibility pattern(s) to antimicrobials is already known

Narrow (de-escalate) from initial empiric therapy

Question 4

What is minimum inhibitory concentration (MIC)?

Answer 4

Drug concentration at which organism’s growth is inhibited

Question 5

What is minimum bactericidal concentration (MBC)?

Answer 5

Drug concentration at which organism death occurs, will exceed MIC

Question 6

How is susceptibility determined?

Answer 6

MIC value + clinically achievable drug concentrations at the site of infection

BOTH must be taken in to account

Question 7

What are the ideal antibiotic properties?

Answer 7

Selective toxicity

Easily classified

No acquired resistance

Question 8

What is a superinfection? How do they develop?

Answer 8

A new infection that appears during the treatment of a primary infection

Develop when Abx kill microbiota that normally inhibit pathogens –> dysbiosis

Question 9

Superinfections are most likely to occur as a result of what type of antibiotics?

Answer 9

Broad spectrum Abx

Question 10

Natural vs Acquired Resistance:

Answer 10

Natural
- the organism has an inherent trait that makes it resistant to the drug

Acquired
- Enzymes that modify/inactivate the drug
- Altered ability to accumulate the drug
- Modified site of action
- Altered cell surface permeability to drug

Question 11

How does acquired resistance occur?

Answer 11

Spontaneous genetic mutations during DNA replication (vertical transfer)

Acquisition of genetic mutations in horizontal transfer

Question 12

Vertical transfer vs. Horizontal transfer

Answer 12

Vertical transfer:
- Once the mutated genes conferring resistance have been created, they are transferred directly to all the bacteria’s progeny during reproduction/binary fission

Horizontal transfer:
- Conjugation
- Transformation
- Transduction

Question 13

Describe the three types of horizontal transfer

Answer 13

1. Conjugation: cell-to-cell contact results in the direct transfer of small pieces of DNA called plasmids
2. Transformation: DNA is taken up by the bacteria from the external environment. This DNA is normally present due to the death and lysis of another bacterium
3. Transduction: Bacteria-specific viruses transfer DNA between two closely related bacteria

Question 14

What are beta-lactam antibiotics? How can they be inactivated?

Answer 14

Antibiotics that contain a beta-lactam ring

They are highly susceptible to the enzyme beta-lactamase, which breaks the beta-lactam ring and renders the drug inactive

Question 15

Describe the relationship between MRSA and PBPs

Answer 15

MRSA (certain strains of S. aureus have acquired genes that code for PBPs that have a very low affinity for penicillins and cephalosporins

Low affinity PBPs –> penicillins and cephalosporins cannot bind to those PBPs and exert their antibacterial effects

Question 16

What clinical presentation does MRSA have?

Answer 16

Can commonly cause skin and soft tissue infections, such as furuncles and carbuncles, including necrotizing fasciitis

Question 17

What are antibiotic stewardship programs?

Answer 17

Programs that are coordinated interventions designed to improve and measure the appropriate use of antibiotic agents

Promotes the selection of the optimal antibiotic drug regimen (dosing, duration of therapy, and route of administration)

Question 18

What are the 4 general MOA of antibacterial agents?

Answer 18

1. Cell wall active antibacterials
2. Interfere with protein synthesis
3. Interfere with nucleic acids
4. Anti-metabolite antibacterial, such as those interfering with synthesis of a derivative of folic acid

Question 19

Describe the role of transpeptidase in antibiotics that destroy the cell wall

Answer 19

Transpeptidase creates cross bridges between strands of peptidoglycan polymers, which add strength to the cell wall

Abx (penicillin) inhibits transpeptidases, which prevents cross-bridge formation and weakens the cell wall

Question 20

Which class of antibiotics interrupt DNA replication and transcription?

Answer 20

Fluoroquinolones

Question 21

Bactericidal vs Bacteriostatic

Answer 21

Bactericidal: kill bacteria outright

Bacteriostatic: prevent bacterial growth

Question 22

What does it mean when an antibiotic is concentration-dependent?

Answer 22

As the concentration of the drug increases, the rate and extent of bacterial killing increases

Question 23

What does it mean when an antibiotic is time-dependent?

Answer 23

The duration of exposure above the MIC is key

Once the abx reaches a certain concentration, there is not an increased rate of bacterial killing with increasing concentrations of antibiotic

Question 24

What is the post-antibiotic effect of a concentration-dependent antibiotic vs. a time-dependent antibiotic?

Answer 24

Time-dependent: shorter post-antibiotic effect

Concentration-dependent: longer post-antibiotic effect