Mechanism of antibacterial activities of a rice hull smoke extract (RHSE) against multidrug-resistant Salmonella typhimurium in vitro and in mice

Authors: KIM, SUNG PHIL - Ajou University Of Korea; LEE, SANG JONG - Str Biotech Co Ltd; NAM, SEOK HYUN - Ajou University Of Korea; Friedman, Mendel

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2017
Publication Date: 12/21/2017
Citation: Kim, S., Lee, S., Nam, S., Friedman, M. 2017. Mechanism of antibacterial activities of a rice hull smoke extract (RHSE) against multidrug-resistant Salmonella typhimurium in vitro and in mice. Journal of Food Science. 82(2):440-445. https://doi.org/10.1111/1750-3841.14020.
DOI: https://doi.org/10.1111/1750-3841.14020

Interpretive Summary: Rice hulls, accounting for about 20% the worldwide production of rice estimated at about 741 million tons in 2014, are a byproduct of postharvest rice processing, Rice hulls can serve as raw materials for various industrial products including the production of adsorbents, activated carbon, and bioethanol. There is also interest in utilizing rice hulls and rice hull smoke as a new flavoring and health-promoting additive for food. To help stimulate interest in this food-processing byproduct we are exploring the potential value of a novel rice hull smoke preparation as a health-promoting multifunctional food additive for human foods and animal feeds. The studies conducted here showed that a rice hull smoke extract, created from a byproduct of rice processing, inactivated a multidrug-resistant strain of Salmonella Typhimurium in vitro and in infected mice. The fight against multidrug resistance is an ongoing one, leading to the investigation of naturally derived alternatives that have antimicrobial and other health-promoting properties. Oral administration of the he rice hull extracted to mice infected with up to 107 colony-forming-units (CFUs) of the resistant Salmonella strain inhibited the growth of the pathogens in the digestive tract and several organs (cecum, mesenteric lymph node, liver, and spleen) and increased the bacterial fecal count. Because antibiotic-resistant bacteria are prevalent in foods and are also of concern in animal and human medicine, there is a need to develop new antimicrobials that can inhibit the growth of resistant bacteria. 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 human foods and farm animal feeds.

Technical Abstract: The present study tested antibacterial activity of a rice hull smoke extract (RHSE) against a multidrug-resistant strain of Salmonella Typhimurium and examined its mode of suppressive action in vitro and in mice. In vitro studies in laboratory media showed that the minimum inhibitory concentration (MIC) value of RHSE was 1.29% (v/v). The validity of the inactivation was confirmed by complete loss of cell viability in the range of 104 to 107 CFUs of the resistant S. Typhimurium strain. Agarose and SDS polyacrylamide gel electrophoreses were used to evaluate the integrities of bacterial genomic DNA and total cellular protein profiles, respectively. The results show that the antibacterial action of RHSE results from a leakage of intracellular macromolecules following the rupture of the bacterial cells. Scanning electron microscopy (SEM) of the cells shows that RHSE also induced deleterious morphological changes in the bacterial cell membrane of the pathogens. In vivo antibacterial activity of RHSE at a 1 × MIC concentration was also examined in a bacterial gastroenteritis animal model using Balb/c mice orally infected with the S. Typhimurium. 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 of RHSE both in vitro and 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 susceptible and antibiotic-resistant foodborne microorganisms.