Efficacy of some indigenous essential oils against bacteria and fungi of public health importance

Abstract

Many pathogenic bacteria and fungi have been reported for causing numerous cases of diseases, illness, and various disorders which have been of important concern to public health. Commercial antimicrobial drugs have been used for combating infectious diseases for past few decades but there are many drawbacks regarding indiscriminate use of antimicrobial drugs including drug resistance, need for long term therapy, relatively high cost and treatment failure. So , there is increasing efforts in finding safer and alternative means to reduce microbial growth. Plants derived natural products are big source of therapeutic drugs for treating various health disorders, acting as potential alternates to antibiotics against infectious diseases. EOs has been known for many decades for their biological activities and are widely used for different functions such as bactericidal, virucidal, fungicidal, insecticidal and pharmaceuticals. Antimicrobial activities of EOs results in the screening of a wide range of plant species and their unique biologically active compounds. Mostly EOs consist of chemical components such as terpenoid including monoterpenes, sequiterpenes and their oxygenated derivatives. The study was conducted to investigate the antimicrobial activity of some indigenous essential oils (EOs) extracted by hydrodistillation from spices such as Cuminum cyminum, Amomum subulatum, Cinnamomum verum, Syzygium aromaticum and citrus peels such as Citrus sinensis against Eschericia coli, Salmonella typhi, Staphylococcus aureus, Bacillus subtilis, multi drug resistant S. aureus (MDRSA) clinical isolates, Aspergillus flavus and Candida albicans by performing the disc diffusion assay and minimum inhibitory concentration (MIC) in vitro and in vivo wound healing activity and antibacterial effect of EOs were studied in rabbits infected with S. aureus and treatment was done at infected site immediatly with EOs. The phytochemical characterization of indigenous EOs and chemical composition of EOs were analyzed by TLC and GC/MS. The antibacterial activities of the components of indigenous EOs were analyzed by TLC-Bioautography. Indigenous EOs showed significant antibacterial activity against all microbial species tested but the highest antibacterial activity was showed against Gram positive bacteria, S. aureus, which was highest by the EO of C. verum with inhibitory zones (34±2.0 mm). In case of Gram negative bacteria such as E. coli, the widest spectrum of antibacterial activity was exhibited by EO of C. sinensis (34±1.5 mm). The results of the antifungal activities indicatedthat volatile EOs were more effective against fungi as compared to bacteria and C. albicans was more susceptible as compared to A. flavus. The EO of C. sinensis had excellent inhibitory activity with the biggest zone of inhibition (55±0.5 mm) against C. albicans and also against A. flavus with wide inhibition zone (53.6±0.8 mm). Results indicated that EOs showed much greater inhibitory activity as compared to the positive control. The result of MICs of indigenous EOs showed that C. sinensis EO was most effective in inhibiting the growth of both bacteria and fungi i.e. E. coli and C. albicans, showing the lowest MIC of 0.0007±0.0001 mg/ ml and 0.0007±0.0006 mg/ ml. Wound healing activity showed that rabbits treated with indigenous EOs showed significantly efficient wound healing activity after 4- 8 days of S. aureus infection depending on the concentration of indigenous EO applied as compared to antibiotic used. Most efficient healing was showed by C. verum EO and C. sinensis EO, which not only healed wound completely after 4 days of infection with dose of 1.5 mg/ml of EOs applied topically only once, but also caused remarkable decreased in viable S. aureus count after 6 days from 7.4×10 6 cfu to 7.6×10 5 cfu and 7.5×10 6 cfu to 7.3×10 5 cfu respectively. GC/MS analysis of indigenous EOs depicted that C. cyminum EO contained Cuminaldehyde 11.5% and ɣ-Terpinene 15.48 %, A. subulatum EO contained major component eucalyptol 5.2 %, C. verum EO contained t-cinnamaldehyde 4.3 % and C. sinensis EO showed that dipentene 0.62 % as a major component was present. These major components of indigenous EOs were confirmed by TLC- bioautography, using microbial culture i.e. E. coli, B. subtilis, S. typhi, S. aureus, MDRSA-1 and MDRSA-2 and it was confirmed that they were bioactive components responsible for the antimicrobial activity by showing zone of inhibition against microorganisms on TLC plate which were comparable by reference standards having similar Rf value. It was concluded that EOs extracted from indigenous plants showed more effective antimicrobial activity against microorganisms in vitro as well as in vivo as compared to the positive and negative control. Chemical composition of indigenous EOs by GC/ MS provided good source for isolation and identification of bio active components. TLC- Bioautographic assay proved efficient method for confirming the presence of bioactive compounds against test bacterium indicating. Hence, EOs proved to be the good substitute of antibiotics against test microorganisms.