Synergistic interactions between Labiatae species and antibiotics on gram positive and gram negative bacterial strains
Objective and methods: This study was aimed to evaluate antibacterial activity; type of interaction between chloroform leaves extract of Mentha piperita, Mentha longifolia and Ocimum basilicum together and with antibiotics by agar well diffusion method on isolated bacterial strain and to determine active constituents responsible on antibacterial activity by agar overlay bioautographic method. Results: Mentha piperita exhibited more pronounced inhibition zone (20mm) against Staphylococcus aureus, Staphylococcus auricularis , Streptococcus mitis and Escherichia coli followed by Mentha longifolia highest inhibition zone (15mm) against Staphylococcus auricularis and Streptococcus mitis , then Ocimum basilicum exhibited highest inhibition zone (14mm) only against Staphylococcus auricularis . As a result of combination chloroform leaves extract with each other the strongest synergistic activity exhibited during combination of Mentha longifolia with Ocimum basilicum (14 to 25mm) against Escherichia coli , while during combination of leaves extract with antibiotics the greatest synergistic activity resulted from combination of Mentha piperita with azithromycin and ampicillin separately (14 to 30mm) and (10 to 23mm) against Escherichia coli and Streptococcus mitis respectively. Escherichia coli revealed susceptibility to all leaves extract and antibiotics alone and pronounced increase in susceptibility to combination of leave extract with each other and with antibiotics. Bioautography assay showed presence number active constituents with antibacterial activity in leaves extract in which three of them identified as caffeic acid, luteolin and rosmarinic acid. Conclusion: From the result concluded that Mentha piperita showed strongest activity followed by Mentha longifolia then Ocimum basilicum alone and there activity increased in combination form.