Evaluation of the in vitro antibacterial activity and minimum inhibitory concentration of Curcuma longa L., Ocimum sanctum L. and Piper nigrum L. ethanolic and aqueous extracts

The study was conducted to evaluate the in vitro antibacterial activity and minimum inhibitory concentration (MIC) of Curcuma longa L., Ocimum sanctum L. and Piper nigrum L. ethanolic and aqueous extracts against Staphylococcus aureus, Streptococcus agalactiae, Bacillus cereus, Listeria monocytogenes, Escherichia coli and Pseudomonas aeruginosa was carried out. ABST was performed using the disc diffusion method while MIC of all six extracts were determined by micro-broth dilution technique against all six bacteria. The extracts were suspended in a solution containing 10% dimethyl sulfoxide and 0.5% tween 80. Under aseptic condition, empty sterilized discs were impregnated with 50 mu l of different (50%, 20%, 10% and 5%) of all six extracts and placed on the agar plate surface. Sterile disc moistened with vehicle (DMSO plus tween 80) was placed on the seeded petri plate as a vehicle control. Standard disc containing antibacterial drugs (gentamicin, tetracycline, cefpirome and ampicillin) were used as reference control. The petri plates were incubated at 37 degrees C for 18 h. After the incubation period, the zone of inhibition was measured. Antibacterial sensitivity test revealed that ethanolic extracts of C. longa, O. sanctum and P. nigrum showed antibacterial activities against Staphylococcus aureus, Bacillus cereus and Listeria monocytogenes whereas O. sanctum ethanolic extracts also showed inhibitory effect against Streptococcus agalactiae. O. sanctum aqueous extract exhibited antibacterial activity against Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes and Escherichia coli, while C. longa aqueous extract showed antibacterial activity against Listeria monocytogenes. Standard antibiotics (gentamicin, tetracycline, cefpirome and ampicillin) were also found active against tested bacteria. The results revealed that ethanolic extract of O. sanctum showed lower MIC against Staphylococcus aureus, Streptococcus agalactiae, Bacillus cereus, Listeria monocytogenes and Escherichia coli than C. longa and P. nigrum ethanolic extracts. Aqueous extract of C. longa showed lower MIC against Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes and Escherichia coli than O. sanctum and P. nigrum aqueous extract. P. nigrum showed lower MIC against Streptococcus agalactiae than C. longa and O. sanctum aqueous extract. All six ethanolic and aqueous extracts were showed no antibacterial activity against Pseudomonas aeruginosa.