Antimicrobial activity of Piper nigrum L. and Cassia didymobotyra L. leaf extract on selected food borne pathogens

To investigate the antimicrobial activity of leaf extract of Piper nigrum (P. nigrum) and Cassia didymobotyra (C. didymobotyra) (aqueous, methanol, ethanol and petroleum ether) against the food borne pathogenic bacteria [Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), Salmonella typhimurium and Pseudomonas aeruginosa)] and fungi [Aspergillus spp. and Candida albicans (C. albicans)] and also to investigate the presence of various phytochemicals in the leaf extracts of tested plants. The antimicrobial activity was determined by disc diffusion method. Minimum inhibitory concentration (MIC), minimum bactericidal and fungicidal concentration were determined by serial dilution method. Methanol leaf extract of test plants exhibited greater antimicrobial activity against the selected bacterial and fungal strains. The MIC results showed that ethanol, methanol and petroleum ether leaf extract of P. nigrum inhibited the growth of S. aureus and E. coli at concentration of 12.5 mg/mL. While, ethanol and methanol leaf extracts of C. didymobotyra inhibited the growth of S. aureus at concentration of 6.25 mg/mL. The MIC values for ethanol, methanol and petroleum ether leaf extract of P. nigrum inhibited the growth of C. albicans at concentration of 25.0 mg/mL. While, it was reported that at concentration of 12.5 mg/mL methanol leaf extract of P. nigrum was against the Aspergillus spp. The MIC values of methanol leaf extract of C. didymobotyra inhibited the growth of C. albicans and Aspergillus spp. at concentration of 12.5 mg/mL and 6.25 mg/mL, respectively. The minimum bactericidal concentration of ethanol, methanol leaf extract of P. nigrum for E. coli and ethanol, methanol leaf extract of C. didymobotyra for S. aureus was recorded at concentration 12.5 mg/mL. The minimum fungicidal concentration of ethanol and methanol leaf extract of P. nigrum and C. didymobotyra on C. albicans was recorded at concentration of 25.0 mg/mL, while, it was found at concentration of 50.0 mg/mL for petroleum ether and aqueous leaf extract of P. nigrum and C. didymobotyra. However, the MIC of methanol leaf extracts of P. nigrum and ethanol and methanol leaf extracts P. nigrum and C. didymobotyra for Aspergillus spp. was recorded at concentration of 12.5 mg/mL, while, the MIC concentration ranged from 25.0–50.0 mg/mL for other tested solvent leaf extract of P. nigrum and C. didymobotyra. This study suggests that test plants could be potential candidates for developing the new antimicrobial drugs against the wide range of pathogenic bacteria and fungal strains.