Antimicrobial effect of black pepper petroleum ether extract for the morphology of Listeria monocytogenes and Salmonella typhimurium

This study aimed to evaluate the effects of black pepper petroleum extract (BPPE) on pathogenic bacteria. The extraction from black pepper showed intense antimicrobial activity against the Gram-positive Listeria monocytogenes ATCC 19115 and the Gram-negative bacteria Salmonella typhimurium ATCC 14028. The minimum inhibitory concentrations of BPPE against L. monocytogenes and S. typhimurium were 0.625 and 1.25 mg/ml, respectively. Detection of Alkaline phosphatase outside the cell revealed that BPPE treatment destroyed the cell wall integrity. BPPE also altered the membrane integrity, thereby causing leaching of 260 and 280 nm UV-absorbing materials into the medium, particularly, nucleic acids and proteins. Propidium iodide infiltration experiments also indicated that BPPE treatment altered the permeability of bacterial cell membrane. Moreover, Na+/K+-ATPase activity was inhibited by BPPE. And the results of scanning electron microscopy showed that BPPE treatment damaged the morphology of the tested bacteria. These results indicated that BPPE could destroy cell wall integrity, alter the permeability of cell membrane, and inhibit the activity of intracellular enzyme, which could kill bacteria.