Additive effect of Lygodium venustum SW. in association with gentamicin

Abstract The aim of this work was to evaluate the interactions between gentamicin and the ethanol extract of the fern Lygodium venustum SW (EELV). The ethanol extract of L. venustum was obtained, the phytocompounds were identified and the EELV was assayed by the checkerboard method with gentamicin against two bacterial strains multiresistant to antibiotics. The antibiotic activity of gentamicin, when associated with the extract, was enhanced in an additive manner against both strains. The results indicated that L. venustum can be a source of secondary metabolites to be used in association with antibiotics as aminoglycosides in the antibiotic chemotherapy against resistant bacteria.


Introduction
Lygodium venustum SW. is a fern that belongs to the Lygodiaceae family, commonly found in the Latin America. This fern is used in the traditional medicine for the treatment of dermatosis, infections, mycosis, thrichomoniasis and other diseases (Shlaes et al. 1997;Duke 2008). This

ABSTRACT
The aim of this work was to evaluate the interactions between gentamicin and the ethanol extract of the fern Lygodium venustum SW (EELV). The ethanol extract of L. venustum was obtained, the phytocompounds were identified and the EELV was assayed by the checkerboard method with gentamicin against two bacterial strains multiresistant to antibiotics. The antibiotic activity of gentamicin, when associated with the extract, was enhanced in an additive manner against both strains. The results indicated that L. venustum can be a source of secondary metabolites to be used in association with antibiotics as aminoglycosides in the antibiotic chemotherapy against resistant bacteria. plant was pharmacologically assayed against gastric diseases and antibacterial activity (Calzada et al. 2007(Calzada et al. , 2010. Recently, many natural products had been tested to verify not only the antibacterial activity, but also the modulatory antibiotic activity as a strategy to combat bacterial pathogens with drugs multiresistance (Hemaiswarya et al. 2008). Many researches about this topic had been developed because the growing problems associated with the loss of the activity of drugs used in the bacterial chemotherapy due the bacterial mechanisms of resistance (Coutinho, Costa, et al. 2009;Coutinho, Vasconcellos, et al. 2009;Coutinho et al. 2010). The aim of this work was to evaluate the interactions between the ethanol extract of L. venustum (EELV) with gentamicin by the checkerboard method.

Results and discussion
When assayed alone, the EELV did not show any clinically relevant antibacterial activity. However, when the extract was associated with gentamicin, and additive effect with FIC índex = 0.5 against both bacterial strains was observed (Table S3). This result indicates that the EELV and gentamicin, using low concentrations and acting together against the bacteria affected several and different targets in the same moment, affecting the resistance mechanism against the antibiotic. This effect was identified in the Gram-positive and -negative strains, indicating a putative similar target in both strains. Due this fact, a possible mechanism involved in this additivity could be associated with the interaction of the nonpolar phytocompounds from EELV as flavonids, tannins and terpenes with the cell membrane, enhancing the permeability to the antibiotic by alterations on the membrane fluidity. This process is called herbal shotgun or synergistic multitarget effects (Coutinho et al. 2010).
Some studies have demonstrated the synergism between several natural products obtained from plants and animals when associated with drugs used in the antibacterial chemotherapy (Coutinho, Costa, et al. 2009;Coutinho, Vasconcellos, et al. 2009). However, this is the first report about the use of natural products isolated from ferns with this aim, demonstrating this activity. These results demonstrate that the ethanol extract of L. venustum is a source of secondary metabolites that could be used in the antibacterial therapy against pathogenic microorganisms with multiresistance to antibiotics in association with antibiotics, as gentamicin.

Disclosure statement
No potential conflict of interest was reported by the authors.