Table 4 Antibiotic-potentiating activity of the isolated compounds.

From: Looking to nature for a new concept in antimicrobial treatments: isoflavonoids from Cytisus striatus as antibiotic adjuvants against MRSA

  

CIP

ERY

Lut

Apig

Chry

Gen

Daid

Lut

Apig

Chry

Gen

Daid

M116

MICa

30

>120

>120

>120

>120

30

>120

>120

>120

>120

MICb

—

30

—

60

15

3.5

30

—

30

—

R

—

4

—

4

2

2

4

—

4

—

FICI

I

≤0.38 (P)

I

≤0.50 (P)

>0.5 (I)

0.63 (I)

≤0.38 (P)

I

≤0.38 (P)

I

RWW337

MICa

30

>120

>120

>120

>120

30

>120

>120

>120

>120

MICb

—

60

—

60

—

—

30

—

60

—

R

—

8

—

8

—

—

≥2

—

≥4

—

FICI

I

≤0.38 (P)

I

≤0.38 (P)

I

I*

(*)

I*

≤0.50 (P)*

I*

RWW50

MICa

60

>120

>120

>120

>120

30

>120

>120

>120

>120

MICb

—

15

—

30

—

—

—

—

60

—

R

—

2

—

2

—

—

—

—

4

—

FICI

I

>0.5 (I)

I

>0.5 (I)

I

I

I

I

≤0.50 (P)

I

M82

MICa

120

>120

>120

>120

>120

60

>120

>120

>120

>120

MICb

60

30

—

30

—

60

—

—

30

—

R

4

2

—

2

—

4

—

—

2

—

FICI

0.75 (I)

>0.5 (I)

I

>0.5 (I)

I

0.75 (I)

I

I

>0.5 (I)

I

RN6390

MICa

120

>120

>120

>120

>120

120

>120

>120

>120

>120

MICb

—

—

—

—

—

—

—

—

—

—

R

—

—

—

—

—

—

—

—

—

—

FICI

I

I

I

I

I

I

I

I

I

I

CECT 976

MICa

120

>120

>120

>120

>120

120

>120

>120

>120

>120

MICb

—

—

—

30

30

—

—

—

30

—

R

—

—

—

4

2

—

—

—

4

—

FICI

I

I

I

≤0.38 (P)

>0.5 (I)

I

I

I

≤0.38 (P)

I

SA1199B

MICa

120

>120

>120

>120

>120

n.p.

    

MICb

—

10

—

60

60

     

R

—

2

—

8

4

     

FICI

I

>0.5 (I)

I

≤0.38 (P)

≤0.25 (P)

     
  1. Minimal inhibitory concentrations (MICs, µg/mL) of the compound isolated from Cytisus striatus against clinical Staphylococcus aureus, RN6390 and SA1199B when applied alone (MICa) and in combination (MICb) with ciprofloxacin or erythromycin. The MICs of antibiotics are shown in Table 1. Fold reductions of antibiotic MICs in the presence of each phytochemical are also represented (R) as well as Fractional Inhibitory Concentration Index (FICI) values. When FICI ≤ 0.5 (in bold), if the phytochemical has a determinable MIC value itself, the effect is considered as synergy (S); if the phytochemical has no detectable MIC, the effect is called potentiation (P). If FICI > 0.5, the interaction is considered indifferent (I). Erythromycin was not tested against SA1199B. The values presented are the averages of at least three independent assays.
  2. = no decrease or increase in the MIC was observed; n.p. not performed; *no MIC was detected for erythromycin alone against RWW337, but when combined with apigenin and genistein, MIC for erythromycin was found to be at least ½ (not conclusive) and ¼ of the maximal concentration tested, respectively. FICI = FIC(A) + FIC(B), with FIC(A) being the ratio between the MIC of drug A in combination and the MIC of drug A alone and FIC(B) the ratio of the MIC of drug B in combination and the MIC of drug B alone.
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