The aim of this study was to investigate the effects of Baccharis coridifolia essential oil on the Activity of Antibiotics. Assays were performed with ampicillin (10 μg), cephalothin (30 μg), chloramphenicol (30 μg), gentamicin (10 μg) and tetracycline (30 μg) alone and in combination with the essential oil (4% v/v) through the disk diffusion susceptibility test. The results showed the effects of essential oil on the activity of the antibiotics tested. Zones of inhibition of bacterial growth with different diameters were observed surrounding the antibiotic disks, whether or not they were impregnated with the essential oil. The occurrence of the synergistic or antagonistic effect was observed in both bacterial strains assessed—Staphylococcus aureus (ATCC-25923) and Escherichia coli (ATCC-25922). These results show that the use of products derived from plants can, in some cases, interfere with the effectiveness of antibiotics during clinical therapy.
The use of natural products as a therapeutic resource is as old as human civilization. Even with the growing economic power of the large pharmaceutical companies, natural products have not lost their place in therapy, being mistakenly regarded by the population as safe medicines and being increasingly used [
Plants with therapeutic properties used in traditional health care are an important source of new biologically active compounds. They have appeared as part of the traditional health care in many parts of the world for decades and have attracted the interest of several researchers [2-6].
In folk medicine, plants are used concomitantly with conventional medicaments [
Oils and plant extracts have long been used in numerous applications in folk medicine, including the production of topical antiseptics. This was the basis for several scientific investigations aimed at confirming the antimicrobial activity of essential oils [9-13].
Celiktas et al. [
The active ingredients present in plants have been extensively studied in many countries, because new drugs can be developed with this knowledge. Understanding the interactions between drugs and plants can also be useful in therapy (beneficial interaction) and for disease prevention.
Plants of the family Asteraceae are extensively studied for their chemical composition and biological activity, with some supporting the development of new drugs, insecticides and other products [16-18].
About 120 Baccharis species have been studied chemically with 30 of them investigated for biological activity. Generally, the most common compounds are the flavonoids and labdane and clerodane diterpenes, although kaurane diterpenes, triterpenes, germacrene, coumaric acids, trichothecenes, sesquiterpenes and phenylpropanoids are also frequently found. Allelopathic, antimicrobial, antiinflammatory and cytotoxic effects are highlighted in biological activity studies. The most researched species for chemical composition and/or biological activity include B. megapotamica, B. incarum, B. trimera, B. trinervis, B. salicifolia, B. crispa, B. coridifolia, B. dracunculifolia, B. uncinella, B. grisebachii and B. tricuneata [17- 20].
Assessing the biological activity of essential oils produced by B. dracunculifolia, B. uncinella and B. coridifolia Ferronato et al. [
The plant studied was B. coridifolia D. C. (Asteraceae) collected in the Southwest region of Paraná, Brazil, from
November 2006 to November 2007. The essential oils were obtained followed the method described by Onofre et al. [13,17,18,22]. This species was chosen because it is widely used in folk medicine and it contains antimicrobial substances described in previous studies [13,22].
S. aureus (ATCC-25923) and E. coli (ATCC-25922) were used as test microorganisms. Suspensions were prepared in a 0.85% (w/v) NaCl solution, with turbidity level compared to the 0.5 McFarland standard, which approximately corresponds to a concentration of 108 CFU/mL.
Ampicillin (10 μg), cephalothin (10 μg), chloramphenicol (30 μg), gentamicin (10 μg) and tetracycline (30 μg) were selected in the study, because of their availability in primary healthcare. The observational study of bacterial susceptibility to antibiotics was carried out through the disk diffusion susceptibility test (NewprovÒ) [
The disk diffusion susceptibility test was carried out to analyze the effect of the essential oil on antibiotic activity. The essential oil was studied at a 4% concentration, which corresponds to the MIC determined in previous studies for the microorganisms tested here [2-4,13,24-26]. The disks containing the antibiotics in their respective concentrations were impregnated with 20 μL of 4% essential oil (MIC), and then placed on sterile Petri plates containing Mueller-Hinton agar inoculated with 1 mL of bacterial suspensions. After incubating the plates at 37˚C for 48 h, the effect of the essential oil MIC on the activity of antibiotics was observed. Synergistic effect was considered when inhibition zones ≥2 mm diameter were observed surrounding disks containing the essential oil (EO) and the antibiotic (AB). Antagonistic effect was considered when an inhibition zone of smaller diameter was observed around the disks with AB and EO, compared to that developed by the AB disks. Indifferent effect was considered when there was a zone of inhibition surrounding the disks with AB and EO, with a diameter equal to that resulting from the application of the AB alone [