Investigation of the antimicrobial activity of the essential oil of Cymbopogon martini on S. aureus and E. coli biofilms

Biofilms are sessile communities of microbial cells embedded in an exopolymeric secreted matrix that can adhere both to abiotic and living surfaces, serving as a permanent source of contamination. Essential oils (EOs) have different characteristics depending on the plant due to a large number of compounds (eugenol, citral, carvacrol, among others). It has been noticed that EOs have promising antibacterial activity that can be explored as an effective alternative to control biofilms. The aim of this study was to assess the antimicrobial activity of the essential oil of Cymbopogon martini against pre-established single biofilms developed by Staphylococcus aureus and Escherichia coli. Biofilms were developed in 96-well microtiter plates for 24 h at 37 ºC, in an orbital shaker at 120 rpm, being afterwards submitted to EOs aggression for 15, 30 e 60 minutes. The essential oil were dissolved in DMSO (2.0 %) and saline water (0.85 %) with tween 80 (0.5 %) in order to obtain final concentrations of 0,12, 0,48, 0,96 and 1,92 %. Biofilms were characterized, before and after EO treatment, by total biomass, through crystal violet (CV), and number of cultivable bacterial cells, expressed as Log CFU per cm2. The C. martini essential oil did not have any effective antimicrobial action against S. aureus biofilms, since there was no significant reduction of the biofilm cultivable cells and biomass. Conversely, this essential oil showed a promising antimicrobial activity against E.coli biofilms as it was observed a significant reduction of the cultivable biofilm-growing cells, in general, for all the concentrations tested and exposure time periods. Similarly to S.aureus biofilms, the C. martinii essential oil was not effective in reducing the biomass of E. coli. From the data, it can be concluded that under the conditions tested, the C. martinii essential oil was more effective in the inhibition of the bacterial cells entrapped in E. coli biofilms than in the removal of biofilm mass. This inability to remove biofilm s from surfaces can be a drawback since the viable cells remaining within the biofilms after EOs treatment are protected by the exopolysaccharides matrix, allowing its multiplication. To overcome this situation, it would be interesting to assess the anti-biofilm potential of the C. martinii essential oil, as well as its synergistic activity with an antimicrobial agent with biofilm disrupting properties

Effect of essential oils on the planktonic of S. aureus and E. coli cells

The essential oils of aromatic plants and their components have a wide range of applications in ethno-medicine, preservation, food flavoring and fragrances and in the perfume industries. Some essential oils derived from plants have revealed promising antimicrobial activity against a wide range of bacteria, including antibiotic resistant species. The aim of this study was to examine the antimicrobial effect of essential oils of Cinnamomum zeylanicum and Cymbopogon martini against planktonic Staphylococcus aureus and Escherichia coli growth. The antimicrobial activity of the essential oils was checked by bacterial growth, at 37 ºC and 120 rpm, in the presence of increasing concentrations of each essential oil for 24 h. Essential oils were dissolved in DMSO (2.0 %) and saline water (0.85 %) with tween 80 (0.5 %) in order to obtain final concentrations of 0.06 %, 0.09 % and 0.12%, for E. coli, and 0.09 %, 0, 12 %, 0.36 % and 0.48 %, for S. aureus. Bacterial planktonic growth over time was followed by the quantification of the number of viable through cultivation of aliquots in TSA. Data showed that E. coli was more sensitive to the action of both essential oils, since complete planktonic growth inhibition was attained with a concentration of 0.09 % of the essential oil of C. zeylanicum oil and 0.06 % of the essential oil of C. Martini. Conversely, S. aureus was less sensitive to the antimicrobial action of the essential oils. C. zeylanicum essential oil inhibited S. aureus growth only at concentrations of 0.36 % and 0.48 %, after 4 and 2 hours of growth. However, unexpectedly after 24 hours those S. aureus cells recovered gradually their planktonic growth. The data pointed out that it is crucial to check the bacterial behavior in the presence of antimicrobial products in different concentrations and over time due to the possible development of bacterial tolerance towards the mechanisms of action of those products. In fact, antimicrobials may have a positive effect in the early hours of application, as demonstrated by some results of this experiment. However, for longer times, the inhibitory effect of antimicrobials can be reverted by bacteria making ineffective their use as disinfectants in food industries. Addiotionally, the continuous exposure of bacteria to antimicrobials can influence the process of microbial resistance de development and increase. These preliminary results demonstrated the possibility of using essential oils of C. zeylanicum and C. martini against two bacteria that are responsible for foodborne illnesses at low concentrations but only for slightly prolonged periods of exposure

Antibiofilm effect of some main components of essentials oils on E. coli biofilm

Fundação para a Ciência e Tecnologia (FCT)European Community - fund FEDER, through Program COMPETE, Project PTDC/SAUESA/6460912006 /FCOMP-01-0124-FEDER-00748