The inhibitory effect of the methanolic extracts of origanum syriacum and rosmarinus officinalis and their major components on the biofilm formation of clinical isolates of staphylococcus aureus. (c2019)

Abstract

Control of bacterial pathogenesis is becoming more difficult by the day. The emergence of bacterial resistance has made treatment of infections more difficult, a reason why a twist towards traditional medication was made as part of the efforts to control such infections. It is well known that bacterial biofilm formation is directly associated with initiation of bacterial infections, so a new trend in research is to try to inhibit biofilm formation and thus prevent infections. This study aimed at detecting whether the methanolic extract of two natural herbs, Rosmarinus Officinalis (Rosemary) and Origanum syriacum (Zaatar) have the ability to inhibit the biofilms that are produced by a serious pathogen, Staphylococcus aureus, using standard methods. The 21 clinical isolates S. aureus, included in the study, were defined phenotypically and genotypically. Six isolates were found to be methicillin resistant (MRSA) while the remaining 15 were methicillin susceptible (MSSA). The PFGE pulsotypes of the strains determined, allowed for segregation of the isolates into one major clade that was subdivided into two subclades, each, of which, contained a set of more closely related isolates. The rest of the isolates were each individually related to others. Notably, the methicillin susceptible S. aureus strains were more closely related to each other as compared to the methicillin resistant strains, which were either grouped in pairs or individually. Interestingly, few methicillin susceptible isolates obtained from one hospital were more closely related to isolates obtained from a health center, than to other methicillin susceptible isolates from the same hospital. The methanolic extract of each of the two plants (0.1 g/ml) revealed an antibacterial effect at volumes equal or higher than 200 μL for Rosmarinus Officinalis and 150 μL for Origanum syriacum against the S. aureus isolates. It was, however, found that the volumes of 100 and 150 μL of the Rosmarinus Officinalis extracts and 50 and 100 μL of the Origanum syriacum extracts at the lower concentrations of 0.02 g/ml (five times diluted extract) and 0.01 g/ml (ten times diluted extract), of the two plants respectively, significantly inhibited the S. aureus biofilm formation. The contribution of the major components of each of the two herbs to that effect was then determined. The two major components of Rosmarinus Officinalis: α- pinene and camphor at different concentrations inhibited the biofilm formation of all the tested isolates. On the other hand, the two major components of Origanum syriacum: Thymol and Carvacrol at different concentrations did not affect the S. aureus biofilm formation. The results of this study revealed the previously undetermined ability of the tested plants to inhibit the S. aureus biofilm formation and demonstrated the significance of α-pinene and camphor as the effective inhibitors and suggested their use to prevent the serious infections that may be caused by the organism.