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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