myrtle ( myrtus communis l. ) is an evergreen shrub belonging to the family of mirtaceae that grows spontaneously throughout the mediterranean area . in italy
it grows along the coast and in the inner hills , and it is spread especially in the islands , where it is one of the most characteristic species .
myrtus communis had history in the popular and traditional medicine : the essential oil obtained from leaves and , sometimes , flowers and berries has been used for its tonic and balsamic properties , and it is used in flavour and fragrance industries . in sardinia
natural formations are still the main source for the production of a traditional liqueur , that every year reaches 3 million bottles .
essential oils are gaining remarkable interest for their potential multipurpose use as antioxidant , antibacterial , and antiseptic agent [ 14 ] ; the essential oil obtained from the leaves was used in the past for the treatment of lung disorders .  
the isolation of essential oils from myrtus communis leaves is usually obtained by hydrodistillation method with a clevenger - type apparatus , according to the italian official pharmacopoeia .
the chemical composition of the essential oils , analysed by gas / cromatography ( g / c ) , generally exhibits -pinene , 11% ; 1,8-cineole , 16% ; linalool , 12% ; -terpineol , 7% ; and limonene , 5% .
the sardinian myrtle oil is characterized by the lack of myrtenyl acetate and by a higher content of limonene .
.   showed the biological activities of tannins , including anticancer and antioxidant . in our previous studies
( data not published ) the antimicrobial properties of myrtus essential oil against several clinical strains and in particular against helicobacter pylori   were studied , and we obtained encouraging results . considering these results , in this study ,
we have used this essential oil towards strains of m. tuberculosis and strains of mycobacterium avium subsp .
in this study we investigated the antimicrobial properties of the essential oil of myrtus communis against two reference strains : m. tuberculosis h37rv ( virulent strain ) and m. tuberculosis h37ra ( avirulent strain ) and 8 clinical isolates of m. tuberculosis resistant to one or more drugs , collected in the department of biomedical sciences , microbiology of the university of sassari , italy .  
we also studied the antimicrobial properties of the essential oil towards two human strains of mycobacterium avium subsp .
the antibacterial activity of the oil was assessed by the proportional method used for mycobacterium tuberculosis as described in nccls - national committee for clinical laboratory standards .    
briefly , isolate suspensions of m. tuberculosis in 7h9 broth were adjusted to an optical density of 1 mcfarland , and two dilutions , 10 and 10 , were plated onto 7h10 agar with a different concentration of essential oil ( 16% , 14% , 12% , 10% , 8% , 4% , 2% , 1% , and 0.17% v / v ) .  
we also investigated the antimicrobial properties of some components of m. communis and , in particular , limonene , 1 - 8 cineole and -pinene , using the proportional method .
in table 1 we report the data obtained with the essential oil in toto .   towards all the strains of m. tuberculosis , including the extensively drug - resistant ( xdr ) , the oil of m. communis tested showed an mic of 0.17% ( v / v ) , whereas against the two m. paratuberculosis strains showed an mic of 2% ( v / v ) .  
subsequently we tested each different compound ( limonene , 1 - 8 cineole , -pinene ) to see if it had different antimicrobial properties .  
as far as limonene concerned , it showed towards all the strains an mic of 2% ( v / v ) ; about 1 - 8 cineole , for 4 strains , including h37rv , the mic was of 2% ( v / v ) , while the mic shown for other 4 strains was of 16% ( v / v ) ; -pinene showed an mic of 1% ( v / v ) for 3 strains , and for one strain an mic of 2% ( v / v ) , for 3 others an mic of 8% ( v / v ) , and for only one mic was of 16% ( v / v ) ( table 2 ) .
limonene and -pinene are monoterpenic that , according to the literature , are used as expectorant , antalgic , revulsive , antitussive , mucolitic , and decongestant ; about 1 - 8 cineole it is an oxide used as expectorant , mucolitic , and decongestant .  
we compared the activity of our essential oil with four standard antitubercular drugs : streptomycin , isoniazid , rifampin , and ethambutol , performing according to international protocols .
two clinical strains were rifampicin resistant , three strains were resistant to 2 drugs ( one streptomicin and rifampicin resistant , one streptomicin and isoniazid resistant , and one isoniazid and rifampicin resistant ) , one was resistant to 3 drugs ( streptomicin , isoniazid , and ethambutol ) .
the essential oils screened in toto have a better antimicrobial activity than each single compound against all mycobacteria tested .
the results presented here may contribute to the knowledge of the antimicrobial properties of myrtle and our aim is to carry on further studies .
the chemical composition of the essential oil of m. communis exhibited qualitative differences that depended on different geographical areas and from the season in which the leaves were picked up .
the essential oil that we used for antimicrobical in vitro assay contained a high quantity of monoterpenic and oxide that , according to literature , do not have antimicrobical activity
. from our studies emerged that the essential oil in toto might have a good activity towards m. tuberculosis , although the individual compounds ( except -pinene ) showed in all the strains a higher mic .
the results from the myrtle oil in toto showed a good activity towards m. tuberculosis but not toward m. paratuberculosis .
the mic registered against m. tuberculosis was 0.17% ( v / v ) in comparison with an mic of 2% ( v / v ) observed toward m. paratuberculosis .  
a limit of our study is the small amount of the essential oil that did not allow to perform the mic towards all the strains used .
testing and large clinical studies are necessary to verify the potential use of the essential oils of myrtle as antitubercular drug . given the excellent results that we obtained in this study , we would expand the research with further studies , to value the possible cytotoxic effects , and eventually to perform tests using  in vivo  mouse model .
 
 mycobacterium tuberculosis is the etiological agent of tuberculosis . 
 the world health organization has estimated that 8 million of people develop active tb every year and the situation is complicated by an increase of mycobacterium tuberculosis strains resistant to drugs used in antitubercular therapy : mdr and xdr - tb . 
 myrtle leaf extracts , used as an antiseptic in sardinian traditional medicine , have strong antibacterial activity as several investigations showed . in this study we investigated the antimicrobial properties of the essential oil of myrtus 
 communis against clinical strains of m. tuberculosis and m. paratuberculosis . 
1. Introduction
2. Materials and Methods
3. Results and Discussion
4. Conclusions