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Table 1 Synergistic activity of extracts from six Rubiaceae species and rifampicin against Mycobacterium species

From: Extracts of six Rubiaceae species combined with rifampicin have good in vitro synergistic antimycobacterial activity and good anti-inflammatory and antioxidant activities

Extract/rifampicin

Mycobacterial strains

MIC (μg/ml)

FICa

Interpretation

Individualb

Combinationc

Individual

Index

Cephalanthus natalensis/rifampicin

M. smegmatis

17/16

0.531/8

0.03/0.5

0.53

Synergy

0.133/8

0.008/0.5

0.51

Synergy

0.066/8

0.004/0.5

0.5

Synergy

M. aurum

100/78

50/1.21

0.5/0.02

0.52

Synergy

50/9.75

0.5/0.13

0.63

Additive

1.56/19.5

0.02/0.25

0.27

Synergy

M. tuberculosis

40/9

40/1.125

1/0.125

1.125

Non-interactive

5/2.25

0.125/0.25

0.38

Synergy

2.5/2.25

0.063/0.25

0.31

Synergy

Cremaspora triflora/rifampicin

M. smegmatis

23/16

11.5/8

0.5/0.5

1

Additive

5.7/8

0.25/0.5

0.75

Additive

2.88/8

0.125/0.5

0.63

Additive

M. aurum

100/78

6.25/1.21

0.063/0.016

0.08

Synergy

50/2.43

0.5/0.031

0.53

Synergy

25/4.87

0.25/0.063

0.31

Synergy

M. tuberculosis

160/9

40/0.14

0.25/0.016

0.27

Synergy

20/0.56

0.125/0.062

0.19

Synergy

10/1.125

0.062/0.125

0.19

Synergy

Oxyanthus speciosus/rifampicin

M. smegmatis

80/16

20/8

0.25/0.5

0.75

Additive

10/8

0.125/0.5

0.63

Additive

5/8

0.06/0.5

0.56

Additive

M. aurum

60/78

60/78

1/1

2

Non-interactive

30/78

0.5/1

1.5

Non-interactive

15/78

0.25/1

1.25

Non-interactive

M. tuberculosis

170/9

85/2.25

0.5/0.25

0.75

Additive

21.25/2.25

0.125/0.25

0..38

Synergy

5.31/2.25

0.031/0.25

0.28

Synergy

Pavetta lanceolata/rifampicin

M. smegmatis

12/16

6/8

0.5/0.5

1

Additive

3/8

0.25/0.5

0.75

Additive

1.5/8

0.125/0.5

0.63

Additive

M. aurum

100/78

6.25/39

0.063/0.5

0.56

Additive

0.781/39

0.008/0.5

0.51

Synergy

0.391/39

0.004/0.5

0.5

Synergy

M. tuberculosis

120/9

60/2.25

0.5/0.25

0.75

Additive

30/4.5

0.25/0.5

0.75

Additive

7.5/4.5

0.063/.05

0.56

Additive

Psychotria capensis/rifampicin

M. smegmatis

60/16

30/8

0.5/0.5

1

Additive

15/8

0.25/0.5

0.75

Additive

7.5/8

0.125/0.5

0.63

Additive

M. aurum

120/78

30/19.5

0.25/0.25

0.5

Synergy

15/39

0.13/0.5

0.63

Additive

3.75/39

0.03/0.5

0.53

Synergy

M. tuberculosis

630/9

315/4.5

0.5/0.5

1

Additive

157.5/4.5

0.25/0.5

0.75

Additive

78.75/4.5

0.125/0.5

0.63

Additive

Psychotria zombamontana/rifampicin

M. smegmatis

40/16

10/8

0.25/0.5

0.75

Additive

5/8

0.125/0.5

0.63

Additive

2.5/8

0.06/0.5

0.56

Additive

M. aurum

80/78

20/19.5

0.25/0.25

0.5

Synergy

10/19.5

0.125/0.25

0.38

Synergy

5/19.5

0.063/0.25

0.31

Synergy

M. tuberculosis

160/9

80/2.25

0.5/0.25

0.75

Additive

40/2.25

0.25/0.25

0.5

Synergy

20/2.25

0.125/0.25

0.38

Synergy

  1. a FIC fractional inhibitory concentration for individual sample FIC index + = FIC (a) + FIC (b). b MIC minimum inhibitory concentration for individual sample; cMIC of samples in combination