Detection, purification and characterization of a bacteriocinproduced by Bacillus subtilis NK16 exhibits a significantantimicrobial activity against clinical Staphylococcus spp

Bacteriocin is an important antimicrobial peptide that can be used in industrial andmedical fields due to its characteristics of antibacterial, food preservation andanticancer activities. Fifty isolates of Bacillus sp were collected from different soilsamples which were already recognized via morphological and biochemicalidentification process. The isolates were screened for bacteriocin production effectiveagainst Staphylococcus spp in order to select the highest producing isolate. The isolateNK16 showed the maximum bacteriocin production (80 AU/ml) which was furthercharacterized as Bacillus subtilis NK 16 through using API identification system (API20E and API 50CHB). Then, next step was to detect the optimal conditions formaximum bacteriocin production which were found to be brain-heart infusion brothas the best production medium with pH 6, 30oCand 2% inoculum size. Bacteriocinwas partially purified by precipitation with ammonium sulphate and then separationwith sephadex G-150 gel filtration. The specific activity of the resulted partialpurified bacteriocin was increased to 853.33 AU/mg with 38 fold purification and24% yield. The study of bacteriocin characterization revealed that the activity ofbacteriocin was stable after 10 min at 20, 30, 40oC whereas 50% of the bacteriocinactivity was lost after exposure to 50oC and decreased to approximately 20 AU/ml at60,70 and 80 Co. In addition, bacteriocin activity showed stability at pH 6 and 7 for 30min while it was decreased by approximately 50% at pH 5 and 8, and completelyinhibited at pH 4 and 9. On the other hand, the investigation of mode of actionshowed that bacteriocin has a bactericidal activity. Antimicrobial activity tests of thepartial purified bacteriocin displayed a significant activity against most clinicalStaphylococcus aureus and Staphylococcus epidermidis isolates, whereas it was lesseffective against Staphylococcus saprophyticus isolates.