Purification of antibacterial proteins from Coffee senna (Senna occidentalis) seeds

Senna occidentalis (L.) Link formally known as Cassia occidentalis is a popular herb in folk medicine for the treatment of a wide range of microbial infections. Crude, ammonium sulphate precipitated and dialyzed proteins of S. occidentalis seeds were evaluated for their antibacterial potential by agar well diffusion and broth dilution techniques, against ten bacterial isolates made up of five Gram positive bacteria; Staphylococcus aureus, Streptococcus pyogenes, Enterococcus Sp, Listeria monocytogene and Bacillus subtilis and five Gram negative bacteria; Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Salmonella typhi and Shigella dysentria. The proteins were isolated by gel filtration on sephadex G-75 column and tested for antibacterial activity. The crude, dialyzed and precipitated proteins were active against all Gram positive bacterial isolates tested but were inactive against all Gram negative bacterial isolates used. The Minimum Inhibitory Concentration (MIC) of the crude, precipitated and dialyzed proteins against the most significantly (p < 0.05) sensitive bacterial B. subtilis were 0.67, 0.73 and 3.34 mg/ml respectively while the Minimum Bactericidal Concentration (MBC) were 2.67, 1.46 and 6.67 mg/ml respectively. Isolation however, resulted in total loss of antibacterial activities. SDS/PAGE analysis showed that the seed contains different proteins with molecular weights ranging from 14,400 to 66,200 kDa. The results of this study suggest that S. occidentalis seed contains proteins that have narrow spectrum, synergetic antibacterial activity against important food spoilage bacterial and can therefore be exploited for the development of novel antibacterial agent(s) for food preservation.