Open Access

Thai ethnomedicinal plants as resistant modifying agents for combating Acinetobacter baumannii infections

  • Pinanong Na Phatthalung1,
  • Sasitorn Chusri2 and
  • Supayang P Voravuthikunchai1Email author
BMC Complementary and Alternative MedicineBMC series ¿ open, inclusive and trusted201212:56

DOI: 10.1186/1472-6882-12-56

Received: 19 March 2012

Accepted: 26 April 2012

Published: 26 April 2012

Abstracts

Background

Acinetobacter baumannii is well-recognized as an important nosocomial pathogen, however, due to their intrinsic resistance to several antibiotics, treatment options are limited. Synergistic effects between antibiotics and medicinal plants, particularly their active components, have intensively been studied as alternative approaches.

Methods

Fifty-one ethanol extracts obtained from 44 different selected medicinal plant species were tested for resistance modifying agents (RMAs) of novobiocin against A. baumannii using growth inhibition assay.

Results

At 250 μg/ml, Holarrhena antidysenterica, Punica granatum, Quisqualis indica, Terminalia bellirica, Terminalia chebula, and Terminalia sp. that possessed low intrinsic antibacterial activity significantly enhanced the activity of novobiocin at 1 μg/ml (1/8xminimum inhibitory concentration) against this pathogen. Holarrhena antidysenterica at 7.8 μg/ml demonstrated remarkable resistant modifying ability against A. baumannii in combination with novobiocin. The phytochemical study revealed that constituents of this medicinal plant contain alkaloids, condensed tannins, and triterpenoids.

Conclusion

The use of Holarrhena antidysenterica in combination with novobiocin provides an effective alternative treatment for multidrug resistant A. baumannii infections.

Background

An underestimated nosocomial pathogen, Acinetobacter baumannii, is now widely acknowledged as a common bacterium in hospital irrigation and intravenous solutions. It possesses inherent multidrug-resistance (MDR) and the ability to rapidly colonize and infect patients. Moreover, the emergence of acquired MDR by A. baumannii to conventional antibiotics presents a serious therapeutic problem in the treatment of the infections [1, 2]. Several investigations suggested that synergy effects of plant secondary metabolites and conventional antibiotics could be an alternative way to increase the bacterial susceptibility [36].

Plants, particularly ethnomedicinal plants are important sources of natural products. They are rich in a wide variety of secondary metabolites such as tannins, terpenoids, alkaloids, and flavonoids and have been well-established to possess antimicrobial properties [7]. Many plants have been evaluated not only for their inherent antimicrobial activity, but also for their action as a resistant modifying agent (RMA) [4].

Novobiocin, a Gyr B inhibitor, is an effective aminocoumarin drug for the treatment of Gram-positive bacterial infections. However, its low level of activity against Gram-negative pathogens causes a major limitation [8]. Although, several investigations observed synergy and mechanisms of action between natural products and synthetic drugs in effectively combating Gram positive bacterial infections [5], there are a few RMA effective for use with A. baumannii[9, 10]. Therefore, the aim of this study was to further explore the resistant modifying activity of a wide range of medicinal plants according to their ethnobotanical basis in combination with novobiocin against A. baumannii.

Methods

Bacterial strain and culture condition

Acinetobacter baumannii ATCC 19606 was employed in this study as a model reference strain. The strain was susceptible to ciprofloxacin, colistin, imipenem, and tobramycin and resistant to amikacin, ampicillin, azithromycin, erythromycin, and gentamicin which conducted by disc diffusion method [11]. Well-isolated colonies of A. baumannii ATCC 19606 were grown in Mueller Hinton Broth (MHB) (Difco Laboratories, Detroit, MI) at 37°C for 18–24 h. The culture density was adjusted to McFarland standards No. 0.5 and resuspended in MHB to obtain a final concentration of 1 × 106 cfu/ml.

Medicinal plant materials

Tested medicinal plants are shown in Table 1. Fifty-one ethanol extracts of 44 Thai medicinal plant species were kindly provided by the Natural Products Research Center, Prince of Songkla University, Hat Yai, Thailand [12]. Collected plant materials were washed with distilled water and dried at 60°C overnight. Ground plant material was macerated with 95% ethanol (1:2 w/v) for 7 days. The extract was filtered and evaporated using rotary evaporator at 45°C until it became completely dry. A stock solution (200 mg/ml) was prepared by dissolving 0.2 g of the dried extract in 1 ml of dimethylsulfoxide (DMSO) (Merck, Germany) and stored at −20°C.
Table 1

Intrinsic antibacterial activity and resistant modifying ability of crude extract (250 μg/ml) in combination with novobiocin (1/8xMIC) against Acinetobacter baumannii ATCC 19606

 

Botanical names

Family name

Part used

%Growth inhibitiona ± SDb

Interpretationc

    

PE

PE + NOV

 

1

Aegle marmelos (L.) Corr. Serr.

Rutaceae

Fruit

22.10 ± 0.68

27.10 ± 1.38

No synergy

2

Ardisia colorata Roxb.

Primulaceae

Fruit

30.17 ± 2.56

39.00 ± 6.09

Synergy

3

Asclepias curassavica L.

Asclepiadaceae

Wood

40.81 ± 0.28

43.59 ± 1.78

No synergy

4

Centella asiatica (L.) Urb.

Apiaceae

Whole

19.09 ± 1.06

23.93 ± 2.87

No synergy

5

Cinnamomum bejolghota (Buch.-Ham.) Sweet

Lauraceae

Wood

58.84 ± 1.37

59.92 ± 1.78

No synergy

   

Bark

55.62 ± 4.98

62.44 ± 2.91

No Synergy

6

Cinnamomum porrectum (Roxb.) Kosterm.

Lauraceae

Wood

29.72 ± 6.54

26.06 ± 5.21

No synergy

   

Bark

56.88 ± 2.14

63.31 ± 4.87

No synergy

7

Curcuma longa L.

Zingiberaceae

Rhizome

86.91 ± 2.64

88.78 ± 2.08

No synergy

8

Curcuma zedoaria (Christm.) Roscoe

Zingiberaceae

Rhizome

77.73 ± 0.48

79.59 ± 2.62

No synergy

9

Derris scandens Benth.

Leguminosea

Stem

49.01 ± 2.37

47.31 ± 3.84

No synergy

10

Dracaena loureiri Gagnep.

Agavaceae

Wood

30.08 ± 0.99

29.49 ± 3.19

No synergy

11

Dryopteris syrmatica (Willd.) Kuntze

Dryopteridaceae

Stem

17.59 ± 0.41

26.66 ± 5.32

Synergy

12

Eleutherine americana (Aubl.) Merr. ex K.

Iridaceae

Bulb

17.87 ± 1.89

22.26 ± 3.12

No synergy

13

Euphorbia thymifolia L.

Euphorbiaceae

Whole plant

53.64 ± 0.90

73.99 ± 0.88

Synergy

14

Garcinia mangostana L.

Clusiaceae

Pericarp

93.25 ± 3.65

90.48 ± 3.37

No synergy

15

Gymnopetalum cochinchinensis (Lour.) Kurz

Cucurbitaceae

Fruit

26.17 ± 0.59

32.45 ± 4.39

No synergy

16

Holarrhena antidysenterica (L.) Wall. ex A. DC.

Apocynaceae

Bark

65.88 ± 0.11

94.04 ± 0.59*

Synergy

17

Impatiens balsamina L.

Balsaminaceae

Stem

9.77 ± 0.30

12.40 ± 1.56

No synergy

18

Manilkara achras (Mill.) Fosb.

Sapotaceae

Fruit

56.59 ± 1.02

63.06 ± 2.97

No synergy

19

Millingtonia hortensis L.f.

Bignoniaceae

Flower

28.97 ± 4.30

54.08 ± 0.83

Synergy

20

Mitragyna speciosa Korth.

Rubiaceae

Leaf

43.33 ± 2.40

66.15 ± 0.26

Synergy

21

Momordica charantia L.

Cucurbitaceae

Vine

22.26 ± 0.85

25.79 ± 3.10

No synergy

22

Morinda citrifolia L.

Rubiaceae

Fruit

16.96 ± 0.63

25.86 ± 1.22

Synergy

23

Murdannia loriformis (Hassk.) R. Rao & Kammathy

Commilinaceae

Whole plant

16.42 ± 1.51

22.04 ± 1.67

No synergy

24

Oroxylum indicum (L.) Vent.

Bignoniaceae

Leaf

67.18 ± 1.59

71.30 ± 5.28

No synergy

25

Peltophorum pterocarpum (DC.) Backer ex K. Heyne

Fabaceae

Flower

42.80 ± 0.43

47.83 ± 4.49

No synergy

   

Bark

78.26 ± 0.60

88.75 ± 6.10

Synergy

26

Piper betle L.

Piperaceae

Leaf

42.72 ± 0.13

39.92 ± 3.43

No synergy

27

Piper nigrum L.

Piperaceae

Fruit

38.07 ± 1.96

42.24 ± 2.60

No synergy

   

Seed

29.07 ± 0.75

31.47 ± 3.27

No synergy

28

Piper retrofractum Vahl

Piperaceae

Fruit

44.02 ± 1.08

49.80 ± 4.19

No synergy

29

Piper sarmentosum Roxb

Piperaceae

Leaf

20.70 ± 0.88

25.02 ± 0.62

No synergy

30

Pluchea indica (L.) Less.

Asteraceae

Leaf

26.64 ± 0.97

53.59 ± 3.60*

Synergy

31

Psidium guajava L.

Myrtaceae

Leaf

71.24 ± 2.00

81.19 ± 1.50*

Synergy

32

Punica granatum L.

Puniceaceae

Pericarp

72.58 ± 1.20

99.29 ± 0.63*

Synergy

33

Quercus infectoria G.Olivier

Fagaceae

Gall

89.09 ± 0.15

88.77 ± 1.00

No synergy

34

Quisqualis indica L.

Combretaceae

Flower

79.22 ± 0.28

94.63 ± 2.62*

Synergy

35

Rhizophora mucronata Lam.

Rhizophoraceae

Fruit

44.64 ± 0.59

53.35 ± 2.56

Synergy

   

Bark

42.68 ± 8.20

53.03 ± 4.95

Synergy

36

Rhodomyrtus tomentosa (Aiton) Hassk.

Myrtaceae

Stem

77.01 ± 1.28

81.81 ± 4.01

No synergy

37

Sandoricum indicum Cav.

Meliaceae

Root

65.24 ± 1.32

66.94 ± 2.13

No synergy

38

Tamarindus indica L.

Fabaceae

Leaf

19.76 ± 1.55

25.03 ± 3.45

No synergy

39

Terminalia bellirica (Gaertn.) Roxb.

Combretaceae

Fruit

74.79 ± 0.53

95.68 ± 1.14*

Synergy

40

Terminalia chebula (Gaertn.) Retz.

Combretaceae

Fruit

61.25 ± 0.42

94.33 ± 1.95*

Synergy

41

Terminalia sp.

Combretaceae

Fruit

79.53 ± 0.24

95.92 ± 1.10*

Synergy

42

Theobroma cacao L.

Sterculiaceae

Pericarp

17.35 ± 0.74

22.81 ± 0.68

No synergy

   

Seed

19.25 ± 1.08

29.61 ± 4.13

Synergy

43

Vitex trifolia L.

Verbenaceae

Leaf

22.12 ± 0.68

28.65 ± 3.57

No synergy

44

Xylocarpus granatum J. Koenig.

Meliaceae

Pericarp

52.39 ± 3.48

53.27 ± 1.91

No synergy

   

Seed

44.27 ± 5.13

54.55 ± 3.66

No synergy

Percentage of growth inhibition of novobiocin against A. buamannii ATCC 19606 was 6.67%.

aPercentage of growth inhibition in the present of plant extract (PE) and plant extract in combination with novobiocin (PE + NOV) against A. buamannii ATCC 19606.

bSD Standard Deviation.

cSynergy: (PE + NOV) > (PE) + (NOV); No synergy: (PE + NOV) < (PE) + (NOV) [6].

*P < 0.01: Significantly different from the effect of plant extract.

Determination of minimum inhibitory concentration (MIC) of novobiocin

The MIC of novobiocin was determined by the broth microdilution method as described by the Clinical and Laboratory Standard Institute (CLSI) [13].

Intrinsic antibacterial activity and resistant modifying ability of medicinal plant extracts

Intrinsic antibacterial activities were determined by growth inhibition assays [9]. The bacterial culture (100 μl) was inoculated into a 96-well microtiter plate containing 50 μl of crude extracts (1,000 μg/ml) and 50 μl of MHB and then incubated at 37°C for 18 h. The intrinsic antibacterial activity was exhibited as the percentage of growth inhibition and calculated from the following equation:
% Growth inhibition = OD A OD B × 100 / OD A https://static-content.springer.com/image/art%3A10.1186%2F1472-6882-12-56/MediaObjects/12906_2012_Article_1052_Equ1_HTML.gif
(1)

Where ODA is Optical density (OD) 595 nm of bacteria culture in MHB supplemented with 1%DMSO as positive control and ODB is OD 595 nm of the bacterial culture in MHB supplemented with plant extracts.

Resistant modifying ability of the extracts was observed by adding of 50 μl novobiocin at a concentration of 1/8xMIC (1 μg/ml) into the tested plate instead of MHB. This biological activity was exhibited as the percentage of growth inhibition as well but calculated from the following equation, where ODC is OD 595 nm of the bacterial culture in MHB supplemented with the plant extract in combination with novobiocin:
% Growth inhibition = OD A OD C × 100 / OD A https://static-content.springer.com/image/art%3A10.1186%2F1472-6882-12-56/MediaObjects/12906_2012_Article_1052_Equ2_HTML.gif
(2)

Effective medicinal plants that demonstrated a synergistic effect with novobiocin and exhibited bacterial growth inhibition more than 90% were selected for further experiments. The efficacy of combination therapy of the promising medicinal plants with novobiocin was additionally determined by measuring the resistant modifying capabilities of the extracts at varying concentrations ranging from 7.8 to 250 μg/ml.

Phytochemical screening methods

Phytochemical screening tests for alkaloids, condensed tannins, flavonoids, hydrolysable tannins, steroids, and triterpenes were qualitatively analyzed by standard colour tests as previously described [14].

Results and discussion

Intrinsic resistance of A. baumannii to novobiocin was observed with MIC value at 8 μg/ml. As shown in Table 1, 48 out of 51 tested ethanol extracts at concentration of 250 μg/ml had low inherent antibacterial activity (% of bacterial growth inhibition was less than 80%). In combination with the antibiotic, the extracts of 18 medicinal plants demonstrated synergistic interaction against A. baumannii. Interestingly, the bacterial growth inhibition in the presence of novobiocin in combination with the extracts of Holarrhena antidysenterica, Punica granatum, Quisqualis indica, Terminalia bellirica, Terminalia chebula, and Terminalia sp. extracts was significantly higher than the intrinsic antibacterial activity of the extracts (Table 1).

To explore the potential of developing a more powerful combination therapy of these medicinal plants with novobiocin, we determined the resistant modifying ability of varying concentrations of the extracts from 7.8 to 250 μg/ml by growth inhibition assay as illustrated in Figure 1. Holarrhena antidysenterica extract which concentrations ranging from 7.8 to 62.5 μg/ml possessed no intrinsic anti-acinetobacter activity (Figure 1A) was demonstrated to be a powerful RMA in combination with novobiocin against this pathogen.
https://static-content.springer.com/image/art%3A10.1186%2F1472-6882-12-56/MediaObjects/12906_2012_Article_1052_Fig1_HTML.jpg
Figure 1

Bacterial growth inhibition of Holarrhena antidysenterica (A), Punica granatum (B), Quisqualis indica (C), Terminalia bellirica (D), Terminalia chebula (E), and Terminalia sp. (F) ethanol extracts () and the extracts in combination with 1/8xMIC of novobiocin () against Acinetobacter baumannii ATCC 19606. Percentage of bacterial growth inhibition of 1/8xMIC of novobiocin on this pathogen was 6.67%.

Our preliminary phytochemical test revealed that alkaloids were common principles among the effective extracts. In addition to alkaloids, other compounds including condensed tannins, triterpenoids, flavonoids, hydrolysable tannins, and steroids were detected (Table 2). Although the antibiotic resistant modifying ability of active principles of the effective medicinal plants has never been investigated, plant-derived alkaloids have been well-clarified as efflux pump inhibitors (EPIs) for Gram positive bacteria [15, 16]. Recent evaluation of 13 phyto-alkaloids for their EPI potential against staphylococcal isolates revealed that 60% and 30% of the tested compounds exhibited the activity against methicillin resistant Staphylococcus aureus (MRSA) and methicillin susceptible S. aureus (MSSA), respectively [16]. Four plant-derived alkaloids consisting of reserpine, quinine, harmaline, and piperine possessed notable potential EPI activities on both MRSA and MSSA [16]. More importantly, their mechanisms of actions as a RMA have been proposed. Piperine was recorded as an inhibitor of MdeA [17] and NorA [18] efflux pumps of S. aureus and Rv1258c efflux pump of Mycobacterium tuberculosis[19]. Reserpine was found as an inhibitor of Bmr efflux pump in Bacillus subtilis, Tet(K) and NorA efflux pumps of S. aureus[20]. In addition to phyto-alkaloids, several plant-derived polyphenols such as epigallocatechin gallate of Camellia sinesis, tellimagrandin I and rugosin B isolated from Rosa canina have been established as useful RMAs with different mechanisms of actions including inhibitions of adapted drug target sites or enzymatic degradation of drugs [4]. Intensive investigations on plant-derived compounds as RMAs have been performed in Gram-positive, but relatively very few studies have been carried out to evaluated RMA activities of plant-derived compounds on Gram-negative bacteria [2123].
Table 2

Extraction yields and phytochemical constituents of tested medicinal plant extracts

 

Botanical names

Part used

Yield (%; w/w)a

Phytochemical constituentsb

    

1

2

3

4

5

6

1

Aegle marmelos (L.) Corr. Serr.

Fruit

5.3

+

+

+

-

+

-

2

Ardisia colorata Roxb.

Fruit

4.4

+

+

-

-

+

-

3

Asclepias curassavica L.

Wood

0.9

+

+

-

-

-

-

4

Centella asiatica (L.) Urb.

Whole

6.0

+

-

-

-

+

-

5

Cinnamomum bejolghota (Buch.-Ham.) Sweet

Wood

2.2

+

+

-

-

+

-

  

Bark

14.6

+

-

-

+

+

-

6

Cinnamomum porrectum (Roxb.) Kosterm.

Wood

11.2

-

-

-

-

+

-

  

Bark

7.0

+

+

-

-

+

-

7

Curcuma longa L.

Rhizome

13.9

+

+

+

-

+

-

8

Curcuma zedoaria (Christm.) Roscoe

Rhizome

13.9

+

+

+

-

-

+

9

Derris scandens Benth.

Stem

3.2

-

+

-

-

+

-

10

Dracaena loureiri Gagnep.

Wood

16.9

-

-

-

-

-

+

11

Dryopteris syrmatica (Willd.) Kuntze

Stem

4.5

+

+

-

-

+

-

12

Eleutherine americana (Aubl.) Merr. ex K.

Bulb

4.8

+

+

-

-

-

-

13

Euphorbia thymifolia L.

Whole plant

1.3

-

+

-

-

+

-

14

Garcinia mangostana L.

Pericarp

5.3

-

-

-

-

-

-

15

Gymnopetalum cochinchinensis (Lour.) Kurz

Fruit

7.6

-

-

-

-

+

-

16

Holarrhena antidysenterica (L.) Wall. ex A. DC.

Bark

2.1

+

+

-

-

-

+

17

Impatiens balsamina L.

Stem

5.2

-

+

-

-

+

-

18

Manilkara achras (Mill.) Fosb.

Fruit

26.7

+

-

+

-

-

+

19

Millingtonia hortensis L.f.

Flower

25.4

+

+

+

-

-

-

20

Mitragyna speciosa Korth.

Leaf

5.9

+

+

-

-

+

-

21

Momordica charantia L.

Vine

3.0

+

-

-

-

+

-

22

Morinda citrifolia L.

Fruit

7.3

+

-

+

-

+

-

23

Murdannia loriformis (Hassk.) R. Rao & Kammathy

Whole plant

7.6

+

-

-

-

+

-

24

Oroxylum indicum (L.) Vent.

Leaf

3.7

+

+

-

-

+

-

25

Peltophorum pterocarpum (DC.) Backer ex K. Heyne

Flower

7.1

+

-

-

-

-

-

  

Bark

7.1

+

+

-

-

-

+

26

Piper betle L.

Leaf

12.4

-

+

-

-

+

-

27

Piper nigrum L.

Fruit

4.2

+

-

-

-

+

-

  

Seed

4.2

+

-

-

-

+

-

28

Piper retrofractum Vahl

Fruit

7.0

-

-

-

-

+

-

29

Piper sarmentosum Roxb

Leaf

1.7

+

-

-

-

+

-

30

Pluchea indica (L.) Less.

Leaf

17.8

+

+

-

-

+

-

31

Psidium guajava L.

Leaf

8.0

+

+

-

-

+

-

32

Punica granatum L.

Pericarp

13.0

+

+

+

-

-

+

33

Quercus infectoria G.Olivier

Gall

37.8

+

-

-

+

-

-

34

Quisqualis indica L.

Flower

11.0

+

-

+

+

+

-

35

Rhizophora mucronata Lam.

Fruit

10.7

+

+

-

-

-

+

  

Bark

11.6

-

+

-

-

-

+

36

Rhodomyrtus tomentosa (Aiton) Hassk.

Stem

7.1

+

+

-

-

-

+

37

Sandoricum indicum Cav.

Root

4.0

+

-

-

-

+

-

38

Tamarindus indica L.

Leaf

4.8

+

+

+

-

+

-

39

Terminalia bellirica (Gaertn.) Roxb.

Fruit

14.8

+

-

-

-

+

-

40

Terminalia chebula (Gaertn.) Retz.

Fruit

5.9

+

+

-

-

-

+

41

Terminalia sp.

Fruit

23.9

+

-

-

+

-

-

42

Theobroma cacao L.

Pericarp

3.6

+

+

-

-

+

-

  

Seed

5.9

-

+

+

-

-

+

43

Vitex trifolia L.

Leaf

NDc

+

+

-

-

+

-

44

Xylocarpus granatum J. Koenig.

Pericarp

2.6

+

+

-

-

+

-

  

Seed

6.7

+

+

+

-

-

+

aPercentage extract yields of medicinal plants were weight of crude extract per 100 g of dried plant materials.

bPhytochemincal constituents: 1, alkaloids; 2, condensed tannins; 3, flavonoids; 4, hydrolysable tannins; 5, steroids and 6, triterpenoids; ‘-’ indicates absence of phytoconstituents ‘+’ indicates presence of phytoconstituents.

cND Not determined.

In the last decade multidrug resistance in A. baumannii became a serious growing problem worldwide. Colistin, an old antibiotic with risk toxicity, has recently been brought back into use to treat MDR bacteria as a stopgap measure until new antibiotics can be developed [24]. A number of workers have proposed the synergistically action combination of conventional antibiotics with RMA act synergistically against MDR Gram-negative bacteria [4, 25, 26]. We have demonstrated that certain plant ethanol extracts significantly enhanced the activity of novobiocin against A. baumannii. Holarrhena antidysenterica is of interest since the extract at 7.8 to 62.5 μg/ml possessed no intrinsic antibacterial activity, but in combination with sub-MIC of novobiocin led to a marked decrease in the bacterial growth. Alkaloids were proposed as active principles of the plant that possessed antibacterial activity on S. aureus S. epidermidis Streptococcus faecalis B. subtilis Escherichia coli, and Pseudomonas aeruginosa[2729]. Some of the alkaloids such as pubadysone, pubescine, norholadiene, pubescimine, puboestrene, pubamide, and naringenin was isolated form bark, seeds, and leaves of this plant [3032].

Our previous investigation demonstrated that ellagic acid which acts as an efflux pump inhibitor exhibited a synergistic effect with novobiocin and other aminocoumarins against both A. baumannii ATCC 19606 and MDR A. baumannii[9]. Ethylenediaminetetraacetic acid and polyethyleneimine that disturb outer membrane permeability have been reported as RMA for novobiocin against P. aeruginosa and Stenotrophomonas morelense[33, 34]. Similarly, berry-derived phenolic compounds that efficiently destabilized outer membrane permeability resulted in increase in novobiocin susceptibility of Salmonella enterica serotype Typhimurium [35].

Since intrinsic novobiocin resistance in A. baumannii is related to the synergistic interaction between limited outer membrane permeability and energy-dependent multidrug efflux pumps [36, 37], the RMA for novobiocin possibly acts as a permeabilizer and/or an efflux pump inhibitor.

Conclusion

The RMA activity of Thai medicinal plants in combination with novobiocin against A. baumannii is reported for the first time. These findings led us to the development of a new generation of phytopharmaceuticals that using plant-derived compounds in combination with existing antibiotics to treat MDR A. baumannii that currently are almost untreatable. Its mechanism of action as well as the active constituents of a promising plant, Holarrhena antidysenterica should be further investigated.

Author’ contributions

PN designed and carried out the study. SC and SV supervised in the design of the study and contributed to the writing process. All authors read and approved the final manuscript.

Declarations

Acknowledgments

This work was supported by the Thailand research Fund-the Commission on Higher Education (MRG 5480069, Fiscal year 2011–2013) and the Higher Education Research Promotion and National Research University of Thailand, Office of the Higher Education Commission.

Authors’ Affiliations

(1)
Natural Products Research Center and Department of Microbiology, Faculty of Science, Prince of Songkla University
(2)
Faculty of Traditional Thai Medicine, Prince of Songkla University

References

  1. Acosta J, Merino M, Viedma E, Poza M, Sanz F, Otero JR, Chaves F, Bou G: Multidrug-resistant Acinetobacter baumannii Harboring OXA-24 Carbapenemase, Spain. Emerg Infect Dis. 2011, 17: 1064-1067.PubMed CentralView ArticlePubMed
  2. Katsaragakis S, Markogiannakis H, Samara E, Pachylaki N, Theodoraki EM, Xanthaki A, Toutouza M, Toutouzas KG, Theodorou D: Predictors of mortality of Acinetobacter baumannii infections: A 2-year prospective study in a Greek surgical intensive care unit. Am J Infect Control. 2010, 38: 631-635.View ArticlePubMed
  3. Hemaiswarya S, Doble M: Synergistic interaction of eugenol with antibiotics against Gram negative bacteria. Phytomedicine. 2009, 16: 997-1005.View ArticlePubMed
  4. Hemaiswarya S, Kruthiventi AK, Doble M: Synergism between natural products and antibiotics against infectious diseases. Phytomedicine. 2008, 15: 639-652.View ArticlePubMed
  5. Ulrich-Merzenich G, Panek D, Zeitler H, Vetter H, Wagner H: Drug development from natural products: exploiting synergistic effects. Indian J Exp Biol. 2010, 48: 208-219.PubMed
  6. Wagner H, Ulrich-Merzenich G: Synergy research: approaching a new generation of phytopharmaceuticals. Phytomedicine. 2009, 16: 97-110.View ArticlePubMed
  7. Perumal Samy R, Gopalakrishnakone P: Therapeutic potential of plants as aAnti-microbials for drug discovery. Evid Based Complement Alternat Med. 2010, 7: 283-294.PubMed CentralView ArticlePubMed
  8. Kampranis SC, Maxwell A: Conversion of DNA gyrase into a conventional type II topoisomerase. Proc Natl Acad Sci U S A. 1996, 93: 14416-14421.PubMed CentralView ArticlePubMed
  9. Chusri S, Villanueva I, Voravuthikunchai SP, Davies J: Enhancing antibiotic activity: a strategy to control Acinetobacter infections. J Antimicrob Chemother. 2009, 64: 1203-1211.View ArticlePubMed
  10. Rosato A, Piarulli M, Corbo F, Muraglia M, Carone A, Vitali ME, Vitali C: In vitro synergistic antibacterial action of certain combinations of gentamicin and essential oils. Curr Med Chem. 2010, 17: 3289-3295.View ArticlePubMed
  11. Clinical and Laboratory Standards Institute: M02-A10-Performance Standards for Antimicrobial Disk Susceptibility Tests Approved Standard-Tenth Edition. 2009, Clinical and Laboratory Standards Institute Wayne, Pennsylvania, USA
  12. Voravuthikunchai SP, Limsuwan S, Chusri S: New Perspectives on Herbal Medicines for Treating Bacterial Infections. Recent Progress in Medicinal Plants: Chronic and Common Diseases-IV. Edited by: Govil GN, Singh VK. 2006, Studium Press, Houstan, Texas, USA, 41-101.
  13. Clinical and Laboratory Standards Institute: M07-A8-Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically Approved Standard-Eighth Edition. 2009, Clinical and Laboratory Standards Institute Wayne, Pennsylvania, USA
  14. Kaur GJ, Arora DS: Antibacterial and phytochemical screening of Anethum graveolens, Foeniculum vulgare and Trachyspermum ammi. BMC Complement Altern Med. 2009, 9: 30-PubMed CentralView ArticlePubMed
  15. Kamicker BJ, Sweeney MT, Kaczmarek F, Dib-Hajj F, Shang W, Crimin K, Duignan J, Gootz TD: Bacterial efflux pump inhibitors. Methods Mol Med. 2008, 142: 187-204.View ArticlePubMed
  16. Mohtar M, Johari SA, Li AR, Isa MM, Mustafa S, Ali AM, Basri DF: Inhibitory and resistance-modifying potential of plant-based alkaloids against methicillin-resistant Staphylococcus aureus (MRSA). Curr Microbiol. 2009, 59: 181-186.View ArticlePubMed
  17. Mirza ZM, Kumar A, Kalia NP, Zargar A, Khan IA: Piperine as an inhibitor of the MdeA efflux pump of Staphylococcus aureus. J Med Microbiol. 2011, 60: 1472-1478.View ArticlePubMed
  18. Nargotra A, Sharma S, Koul JL, Sangwan PL, Khan IA, Kumar A, Taneja SC, Koul S: Quantitative structure activity relationship (QSAR) of piperine analogs for bacterial NorA efflux pump inhibitors. Eur J Med Chem. 2009, 44: 4128-4135.View ArticlePubMed
  19. Sharma S, Kumar M, Sharma S, Nargotra A, Koul S, Khan IA: Piperine as an inhibitor of Rv1258c, a putative multidrug efflux pump of Mycobacterium tuberculosis. J Antimicrob Chemother. 2010, 65: 1694-1701.View ArticlePubMed
  20. Stavri M, Piddock LJV, Gibbons S: Bacterial efflux pump inhibitors from natural sources. J Antimicrob Chemother. 2007, 59: 1247-1260.View ArticlePubMed
  21. Darwish RM, Aburjai TA: Effect of ethnomedicinal plants used in folklore medicine in Jordan as antibiotic resistant inhibitors on Escherichia coli. BMC Complement Altern Med. 2010, 10: 10.1186/1472-6882-10-9.
  22. Fadli M, Saad A, Sayadi S, Chevalier J, Mezrioui NE, Pagès JM, Hassani L: Antibacterial activity of Thymus maroccanus and Thymus broussonetii essential oils against nosocomial infection - bacteria and their synergistic potential with antibiotics. Phytomedicine. 2012, 15: 464-471.View Article
  23. Fadli M, Chevalier J, Saad A, Mezrioui NE, Hassani L, Pages JM: Essential oils from Moroccan plants as potential chemosensitisers restoring antibiotic activity in resistant Gram-negative bacteria. Int J Antimicrob Agents. 2011, 38: 325-330.View ArticlePubMed
  24. Zavascki AP, Goldani LZ, Li J, Nation RL: Polymyxin B for the treatment of multidrug-resistant pathogens: a critical review. J Antimicrob Chemother. 2007, 60: 1206-1215.View ArticlePubMed
  25. Coban AY, Tanriverdi Cayci Y, Erturan Z, Durupinar B: Effects of efflux pump inhibitors phenyl-arginine-beta-naphthylamide and 1-(1-naphthylmethyl)-piperazine on the antimicrobial susceptibility of Pseudomonas aeruginosa isolates from cystic fibrosis patients. J Chemother. 2009, 21: 592-594.View ArticlePubMed
  26. Peleg AY, Adams J, Paterson DL: Tigecycline efflux as a mechanism for nonsusceptibility in Acinetobacter baumannii. Antimicrob Agents Chemother. 2007, 51: 2065-2069.PubMed CentralView ArticlePubMed
  27. Chakraborty A, Brantner AH: Antibacterial steroid alkaloids from the stem bark of Holarrhena pubescens. J Ethnopharmacol. 1999, 15: 339-344.View Article
  28. Kavitha D, Shilpa PN, Devaraj SN: Antibacterial and antidiarrhoeal effects of alkaloids of Holarrhena antidysenterica WALL. Indian J Exp Biol. 2004, 42: 589-594.PubMed
  29. Kavitha D, Niranjali S: Inhibition of enteropathogenic Escherichia coli adhesion on host epithelial cells by Holarrhena antidysenterica (L.) WALL. Phytother Res. 2009, 23: 1229-1236.View ArticlePubMed
  30. Kumar A, Ali M: A new steroidal alkaloid from the seeds of Holarrhena antidysenterica. Fitoterapia. 2000, 71: 101-104.View ArticlePubMed
  31. Siddiqui BS, Usmani SB, Ali ST, Begum S, Rizwani GH: Further constituents from the bark of Holarrhena pubescens. Phytochemistry. 2001, 58: 1199-1204.View ArticlePubMed
  32. Tuntiwachwuttikul P, Pootaeng-on Y, Phansa P, Limpachayaporn P, Charoenchai P, Taylor WC: Constituents of the leaves of Holarrhena pubescens. Fitoterapia. 2007, 78: 271-273.View ArticlePubMed
  33. Alakomi HL, Paananen A, Suihko ML, Helander IM, Saarela M: Weakening effect of cell permeabilizers on gram-negative bacteria causing biodeterioration. Appl Environ Microbiol. 2006, 72: 4695-4703.PubMed CentralView ArticlePubMed
  34. Khalil H, Chen T, Riffon R, Wang R, Wang Z: Synergy between polyethylenimine and different families of antibiotics against a resistant clinical isolate of Pseudomonas aeruginosa. Antimicrob Agents Chemother. 2008, 52: 1635-1641.PubMed CentralView ArticlePubMed
  35. Alakomi HL, Puupponen-Pimia R, Aura AM, Helander IM, Nohynek L, Oksman-Caldentey KM, Saarela M: Weakening of salmonella with selected microbial metabolites of berry-derived phenolic compounds and organic acids. J Agric Food Chem. 2007, 55: 3905-3912.View ArticlePubMed
  36. Damier-Piolle L, Magnet S, Bremont S, Lambert T, Courvalin P: AdeIJK, a resistance-nodulation-cell division pump effluxing multiple antibiotics in Acinetobacter baumannii. Antimicrob Agents Chemother. 2008, 52: 557-562.PubMed CentralView ArticlePubMed
  37. Savage PB: Multidrug-resistant bacteria: overcoming antibiotic permeability barriers of gram-negative bacteria. Ann Med. 2001, 33: 167-171.View ArticlePubMed
  38. Pre-publication history

    1. The pre-publication history for this paper can be accessed here:http://​www.​biomedcentral.​com/​1472-6882/​12/​56/​prepub

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© Na Phatthalung et al.; licensee BioMed Central Ltd. 2012

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