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Table 1 MICs of five antibiotics alone and in the presence of Holarrhena antidysenterica steroidal alkaloids or conessine against P. aeruginosa PAM1020, 1032, 1033, 1034 and 1626

From: Steroidal alkaloids and conessine from the medicinal plant Holarrhena antidysenterica restore antibiotic efficacy in a Galleria mellonella model of multidrug-resistant Pseudomonas aeruginosa infection

Strain

Drug

Drug MIC (mg/L) with

FIC indexb

 

Alone

Steroidal alkaloidsa

Conessinea

Drug + Steroidal alkaloids

Drug + Conessine

PAM1020

CAZ

1

0.5

1

1.50

1.50

PIP

2

1

2

1.50

1.50

MEM

0.5

0.5

0.25

2.00

1.00

LVX

0.5

0.5

0.25

2.00

1.00

AMK

1

0.5

0.5

1.50

1.00

PAM1032

CAZ

4

2

2

1.50

1.00

PIP

16

16

8

2.00

1.00

MEM

4

4

2

2.00

1.00

LVX

2

1

1

1.50

1.00

AMK

1

0.5

0.5

1.50

1.00

PAM1033

CAZ

1

0.5

1

1.50

1.50

PIP

2

1

2

1.50

1.50

MEM

0.5

0.25

0.5

1.50

1.50

LVX

4

4

4

2.00

1.50

AMK

0.5

0.25

0.5

1.50

1.50

PAM1034

CAZ

1

1

0.5

2.00

1.00

PIP

1

0.5

0.03125

1.50

0.53

MEM

0.5

0.5

0.125

2.00

0.75

LVX

4

2

0.25

1.50

0.56

AMK

0.5

0.25

0.5

1.50

1.50

PAM1626

CAZ

0.5

0.5

0.25

1.50

1.00

PIP

0.5

0.25

0.5

1.00

1.50

MEM

0.0625

0.0625

0.0625

1.50

1.50

LVX

0.03125

0.00781

0.00391

0.75

0.63

AMK

0.5

0.25

0.25

1.00

1.00

  1. CAZ ceftazidime, PIP piperacillin, MEM meropenem, LVX levofloxacin, AMK amikacin
  2. aThe concentration of steroidal alkaloids or conessine added to each well reflected the previously characterized MICs and were selected to be lower than the MIC for each strain: PAM1020, 1032, 1033, and 1034: Steroidal alkaloids (1024 mg/L), Conessine (32 mg/L); PAM1626: Steroidal alkaloids (128 mg/L), Conessine (32 mg/L)
  3. bFractional inhibitory concentration index (FIC index) where synergistic (≤ 0.5), non- synergistic (> 0.5 - ≤ 4.0), and antagonistic (> 4.0). For the strains where the steroidal alkaloids did not have a measurable MIC, the highest value tested (1024 mg/L) was used in the FICI calculation to provide a conservative estimate of the FICI value