Chemical Composition and Antibacterial, Anti-biofilm and Anti-virulence Activities of Plant Extracts Against Human Pathogenic Bacteria

Background: Bacterial multi-drug resistance is one of the serious issues worldwide. The majority of drug resistance developed by bacteria is derived from the formation of biofilm and the production of several virulence factors. Objective: To combat the emerging drug resistance nature of bacteria, we have used some medicinal plants such as Stevia rebaudiana, Cymbopogon flexuosus, Matricaria chamomilla, Ocimum sanctum, Phyllanthus amarus and Thymus vulgaris for the extraction of active molecules that can inhibit the biofilm formation and bacterial growth. Materials & Methods: Each extracted compounds were checked for anti-bacterial, anti-biofilm, and anti-virulence activities against Gram-positive and Gram-negative pathogenic bacteria. Soxhlet method of extraction was used for obtaining crude extracts. Agar disc diffusion and 96-wells microplate spectroscopic reading were used to detect the antibacterial and antibiofilm properties of the extracts. Crystal violet staining was used for the detection of biofilm cells. GC-MS analysis was carried out to identify the chemical constituents present in the extracts. Results: At a concentration of 25 mg mL(-1), the highest antibacterial activities were obtained in M. chamomilla acetone extract (CHAAC) against E. coli (17.66 +/- 1.15 mm), S. Typhimurium (13.66 +/- 1.52 mm) and S. sonnei (14 +/- 1.73 mm). M. chamomilla chloroform extracted (CHACE) was shown to be effective against S. aureus (30 +/- 2 mm) and P. aeruginosa (13.66 +/- 1.52 mm). The minimum inhibitory concentration of crude extracts derived from M. chamomilla was 0. 781mg.mL(-1) against S. aureus. Furthermore, the oil extract from C. flexuosus (LEGO) exhibited significant antibacterial activity against S. aureus (at 0.781 mu g mL-1). The potent anti-biofilm activity was observed in G. superba (KALO) against E. coli (78.6%) and S. Typhimurium (79.1%), and V. negundo (VNO) against S. Typhimurium (87.3%). Furthermore, the GC-MS analysis showed the presence of active chemical constituents in the extracts which might have effective anti-bacterial, anti-biofilm, and antivirulence properties. Conclusion: The extracts from the medicinal plant showed antibiofilm, anti-virulence (attenuation of pyocyanin, LasA, violacein, and swarming motility) activity towards the pathogenic bacteria. GCMS analysis confirms the presence of an active component in the extracts. Future study is required to purify the bioactive molecules and elucidate the molecular mechanism of antibiofilm and antivirulence properties.