Antimicrobials Basics

Question 1

MIC minimum inhibitor concentration

Answer 1

Minimum plans concentration of antibiotics required to inhibit visible growth of organisms after 24 hours of incubation

Question 2

Optimal dose of antibiotic

Answer 2

It is the dose of antibiotic that inhibits the growth of 90% of microorganisms at the site of infection

Question 3

Time dependent killing

Answer 3

The antimicrobial effect of such antibiotics is dependent on time during which plasma concentration above MIC
No post antibiotic effect

Question 4

Antibiotics with TDK with no PAR

Answer 4

1. β-lactam 
• penicillin
• cephalosporins
• monobactams
• carbapenems
2. Vancomycin
3. Flucytosine 
Multiple dosing is required

Question 5

Antibiotics with TDK along with prolonged post antibiotic effects

Answer 5

Drugs have cidal effects at very high 🔼🔼 concentration

But they have static effects both at high 🔼 and low 🔽 plasma concentrations

Question 6

Examples of TDK word prolonged post antibiotic effect PAE

Answer 6

Protein synthesis inhibitors like:
1. Erythromycin 
2. Clarithromycin
3. Clindamycin 
4. Linezolid
5. Streptogramins
6. Tetracyclins 
7. Azoles
Effect depends on bioavailability (are under curve)
🔼 dose ➡️🔼 effect

Question 7

Concentration dependent killing

Answer 7

Antimicrobial effect depends on plasma concentration above MIC

Question 8

Examples of concentration dependent killing CHF

Answer 8

1. Aminoglycosides
2. Fluoroquinolones
3. Daptomycin
4. Azithromycin
5. Telithromycin
6. Metronidazole
7. Amphotericin-B
8. Rifampin (movement depends on concentration gradient)

Question 9

Examples of intrinsic drug resistance

Answer 9

1. Aminoglycosides:
   Never active against anaerobes, bcz they can’t enter
2. Vancomycin:
   Not acting against G -ve bacteria
   Large size ➡️ can’t pass through porins
3. Cell wall synthesis inhibitors:
   Not active against mycoplasma

Question 10

Types of acquired resistance

Answer 10

1. Genetic basis
• chromosomal mediated:
    Spontaneous mutation
    Hyper mutation
    Adaptive mutation
• horizontal gene transfer
2. Bio mechanical basis

Question 11

Types of chromosome mediated resistance

Answer 11

1. Spontaneous mutation
2. Hypermutation
   Accelerated mutation
   Eg., MDR TB Beijing type
3. Adaptive mutation:
   E. coli was sensitive to Fluoroquinolones, but not now due to mutation of DNA gyrase

Question 12

Spontaneous mutation and antibiotic resistance

Answer 12

Type of chromosome mediated resistance
Due to faulty DNA replication
via biomechanical changes
Eg.,
1. Rpob gene mutation: rifampin resistance
2. 🔽 porins in G -ve bacteria: Pseudomonas
3. Efflux pumps:
β lactams, Tetracyclines, fluoroquinolone
4. Drug inactivating enzymes: β lactamases

Question 13

Types of horizontal gene transfer

Answer 13

One bacteria to another:
1. Conjugation: M/C
 Plasmid
2. Transduction:
 Bacteriophage
3. Transformation: direct
Within one bacteria:
 Via transposons b/w DNA & plasmid and b/w 2 plasmids 
 Gene cassettes carry information of gene resistance (integron)

Question 14

Biofilm

parts

Answer 14

1. Persisters:
   Initially bacteria which later do not multiply and grow
2. Colony communicating via quorum sensing
3. Exopolysaccharide layer

Question 15

Cause of resistance in biofilms

Answer 15

1. Biomechanical barrier to antibiotics
2. 🔽 replication bcz 🔽 entry off O2 and nutrients
3. Produced efflux pumps
4. Drug inactivating enzymes
5. Persisters (initial central bacteria) with spore like configuration