Mechanism of Antibacterial Activities of a Rice Hull Smoke Extract (RHSE) Against Multidrug-Resistant Salmonella Typhimurium In Vitro and in Mice: Antibacterial activities of an RHSE…

The present study tested antibacterial activity of a rice hull smoke extract (RHSE) against a multidrug‐resistant strain of SalmonellaTyphimurium and examined its mode of suppressive action in vitroand in mice. In vitrostudies showed that the minimum inhibitory concentration (MIC) value of RHSE was 1.29% (v/v). The inactivation was confirmed by complete loss of cell viability in the range of 104to 107colony forming units of the resistant SalmonellaTyphimurium strain. Agarose and sodium dodecyl sulfate–polyacrylamide gel electrophoreses were used to evaluate the integrities of bacterial genomic DNA and total cellular protein profiles. The antibacterial action of RHSE results from a leakage of intracellular macromolecules following rupture of bacterial cells. Scanning electron microscopy of the cells shows that RHSE also induced deleterious morphological changes in the bacterial cell membrane of the pathogens. In vivoantibacterial activity of RHSE at a 1 × MIC concentration was examined in a bacterial gastroenteritis model using Balb/c mice orally infected with the SalmonellaTyphimurium. The results show greatly decreased excretion of the bacteria into the feces and suppressed translocation of the bacteria to internal organs (cecum, mesenteric lymph node, spleen, and liver) compared with the infected mice not subjected to the RHSE treatment. Collectively, the present findings indicate that the mechanism of the antibacterial activities both in vitroand in the gastroenteritis environment of the animal model is the result of the direct disruption of cell structure, leading to cell death. RHSE has the potential to serve as a multifunctional food additive that might protect consumers against infections by antibiotic‐resistant microorganisms. The rice hull derived liquid smoke has the potential to complement widely used wood‐derived smoke as an antimicrobial flavor and health‐promoting formulation for application in foods and feeds.