Table 6 Antimicrobial activity of acetylated peptides in combination with antibiotics.

From: Development of novel broad-spectrum antimicrobial lipopeptides derived from plantaricin NC8 β

Antimicrobial agent

S. aureus

Antimicrobial agent

E. coli

MIC

MBC

ΣFIC/FBC

MIC

MBC

ΣFIC/FBC

L-6-C5 (µM)

6.25

6.25

 

L-6-C5 (µM)

6.25

6.25

 

D-6-C5 (µM)

3.1

6.25

 

D-6-C5 (µM)

3.1

6.25

 

L-6-C5-Leu (µM)

3.1

3.1

 

L-6-C5-Leu (µM)

3.1

3.1

 

D-6-C5-Leu (µM)

3.1

3.1

 

D-6-C5-Leu (µM)

3.1

3.1

 

Vancomycin (µg/ml)

0.78

0.78

 

Gentamicin (µg/ml)

1

1

 

Vancomycin/L-6-C5

  

0.75/1.00

Gentamicin/L-6-C5

  

0.75/1.00

Vancomycin/D-6-C5

  

0.82/0.70

Gentamicin/D-6-C5

  

0.52/0.63

Vancomycin/L-6-C5-Leu

  

0.70/0.75

Gentamicin/L-6-C5-Leu

  

0.75/0.75

Vancomycin/D-6-C5-Leu

  

0.70/0.78

Gentamicin/D-6-C5-Leu

  

0.51/0.51

Rifampicin (µg/ml)

0.062

0.062

 

Rifampicin (µg/ml)

12.5

100

 

Rifampicin/L-6-C5

  

1.06/1.06

Rifampicin/L-6-C5

  

1.06/1.06

Rifampicin/D-6-C5

  

1.03/1.00

Rifampicin/D-6-C5

  

0.53/1.00

Rifampicin/L-6-C5-Leu

  

1.06/1.13

Rifampicin/L-6-C5-Leu

  

0.53/0.50

Rifampicin/D-6-C5-Leu

  

1.03/1.02

Rifampicin/D-6-C5-Leu

  

0.56/0.51

Tetracycline (µg/ml)

0.5

8

 

Cefotaxim (µg/ml)

0.5

0.5

 

Tetracycline/L-6-C5

  

0.53/0.63

Cefotaxim/L-6-C5

  

0.53/0.63

Tetracycline/D-6-C5

  

0.75/0.75

Cefotaxim/D-6-C5

  

0.75/0.75

Tetracycline/L-6-C5-Leu

  

0.63/0.53

Cefotaxim/L-6-C5-Leu

  

0.53/0.56

Tetracycline/D-6-C5-Leu

  

0.53/0.53

Cefotaxim/D-6-C5-Leu

  

0.53/0.56

Ciprofloxacin (µg/ml)

0.25

0.25

 

Ciprofloxacin (µg/ml)

0.125

0.125

 

Ciprofloxacin/L-6-C5

  

0.53/0.37

Ciprofloxacin/L-6-C5

  

0.53/0.37

Ciprofloxacin/D-6-C5

  

0.76/0.75

Ciprofloxacin/D-6-C5

  

0.63/0.63

Ciprofloxacin/L-6-C5-Leu

  

0.63/0.56

Ciprofloxacin/L-6-C5-Leu

  

0.63/0.56

Ciprofloxacin/D-6-C5-Leu

  

0.63/0.63

Ciprofloxacin/D-6-C5-Leu

  

0.63/0.63 s

  1. The antimicrobial activities of acetylated peptides with five carbon atoms, with or without different antibiotics, were determined in checkerboard assays (peptide diluted in PBS and bacteria in LB-broth, with a final volume of 200 µL, with a ratio of 50:50 PBS/broth) against (A) S. aureus (ATCC 29213, Manassas, VA) and (B) E. coli (K-12 MG1655). The fractional inhibitory concentration (FIC) and fractional bactericidal concentration (FBC) shows that the majority peptides interact with the antibiotics in a synergistic or additive manner. Synergy was defined as FIC/FBC ≤ 0.5, additive when 0.5 < FIC/FBC ≤ 1, indifferent when 1 < FIC/FBC < 2 and antagonistic when FIC/FBC ≥ 2.
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