Phytic Acid and Sodium Chloride Show Marked Synergistic Bactericidal Effects against Nonadapted and Acid-Adapted Escherichia coli O157:H7 Strains

Abstract

The synergistic antimicrobial effects of phytic acid (PA), a natural extract from rice bran, plus sodium chloride against Escherichia coli O157:H7 were examined. Exposure to NaCl alone at concentrations up to 36% (wt/wt) for 5 min did not reduce bacterial populations. The bactericidal effects of PA alone were much greater than those of other organic acids (acetic, citric, lactic, and malic acids) under the same experimental conditions (P < 0.05). Combining PA and NaCl under conditions that yielded negligible effects when each was used alone led to marked synergistic effects. For example, whereas 0.4% PA or 3 or 4% NaCl alone had little or no effect on cell viability, combining the two completely inactivated both nonadapted and acid-adapted cells, reducing their numbers to unrecoverable levels (>7-log CFU/ml reduction). Flow cytometry confirmed that PA disrupted the cell membrane to a greater extent than did other organic acids, although the cells remained viable. The combination of PA and NaCl induced complete disintegration of the cell membrane. By comparison, none of the other organic acids acted synergistically with NaCl, and neither did NaCl-HCl solutions at the same pH values as the test solutions of PA plus NaCl. These results suggest that PA has great potential as an effective bacterial membrane-permeabilizing agent, and we show that the combination is a promising alternative to conventional chemical disinfectants. These findings provide new insight into the utility of natural compounds as novel antimicrobial agents and increase our understanding of the mechanisms underlying the antibacterial activity of PA. Food safety has become an increasingly important aspect of public health. According to the World Health Organization, foodborne and waterborne diarrheal diseases kill an estimated 2 million people per year, many of whom are children (1). Although various chemicals are used to control the transmission of foodborne illnesses via the food and livestock industries (2, 3), several studies have suggested that synthetic sanitizers can have significant side effects (e.g., bleaching, formation of toxic compounds, and off odors) (4, 5). Because modern consumers tend to prefer the use of "natural" agents rather than "synthetic" ones (6), new antimicrobial agents are required; therefore, studies of natural compounds with antimicrobial actions are warranted.Organic acids are a class of such natural antimicrobial agents. Several organic acids (particularly acetic, citric, and lactic acids) have long been used as preservatives or surface sanitizers for beef hides (7), carcasses (8), dairy products (9, 10), fresh-cut vegetables (11), and meat products (12). However, organic acids alone are not powerful enough to inactivate pathogenic bacteria after only a short exposure time (5, 13). Even if this problem could be overcome, applying adequate amounts of organic acids is impractical, because they generate strong acidic odors at working concentrations (5, 13). Thus, it is of vital importance to identify new alternatives ...

Tough Polyelectrolyte Hydrogels with Antimicrobial Property via Incorporation of Natural Multivalent Phytic Acid

“…Under neutral pH of bacterial solution, active phosphate groups of PA form chelating complex with divalent cations metal ions (Ca 2+ , Mg 2+ ). The lack of these metal ions leads to the disruption of the membrane of bacteria [60]. Moreover, charged ions such as protons and other ions in solution can easily get into bacterial cells and cause further internal damage to bacterial organelles and DNA [61].…”

Effect of gamma irradiation on inactivation ofEscherichia coliO157:H7,SalmonellaTyphimurium andListeria monocytogeneson pistachios

“…Stress‐adapted micro‐organisms usually show increased resistance to antimicrobial interventions. There are several studies which reported that acid‐adapted food‐borne pathogens showed resistance to control interventions (Buchanan and Edelson, ; Kim and Rhee, ; Chung et al ., ). Hartke et al .…”

A phenotypic screening bioassay forEscherichia colistress and antibiotic responses based on Fourier‐transform infrared (FTIR) spectroscopy and multivariate analysis

“…The following stress agents were evaluated, since these challenge bacteria with a wide range of stresses, thereby providing a broad variety of responses: 10% (v/v) ethanol (Sigma-Aldrich, St. Louis, MO); 8% (w/v) NaCl (Merck); 80 ppm sodium hypochlorite (VWR, Lisboa, Portugal); 2 mol l À1 hydrochloric acid solution (Sigma-Aldrich) corresponding to a final pH of 2Á00; and a 0Á5 mol l À1 sodium hydroxide solution (Fluka, Diegem, Belgium) corresponding to a final pH of 10Á66. These concentrations are adequate to study E. coli stress responses since they are insufficient to induce cell death, as confirmed by cell viability assays in other studies (Foster and Richard 2004;Sharma and Beuchat 2004;Kwak et al 2014;Kim and Rhee 2016;Cao et al 2017). Moreover, each stress agent had a paired control sample, where the stress agent was replaced with distilled sterile water.…”

“…Bacterial responses to stressful events encompass a wide variety of adaptations, many of which have been described for E. coli , including those following exposure to: sodium hypochlorite, a strong oxidizer that up‐regulates over 380 genes and induces faster post‐exposure recovery cell growth (Wang et al ; Kwak et al ); ethanol, which disrupts the membrane and cell wall integrity, reducing O 2 levels and ATP production, as well as fostering DNA damage and a six orders of magnitude increase of protein expression (Soufi et al ; Cao et al ); sodium chloride, which increases water efflux, thereby affecting morphology and reducing maximum growth, ultimately resulting in extensive cell damage and loss of integrity (Hajmeer et al ; Kim and Rhee ; Lee and Kang ,, ; Omotoyinbo and Omotoyinbo ); and acidic environments that activate mechanisms to counteract the pH imbalance (Richard and Foster ; Foster ; Foster and Richard ; Kanjee and Houry ). Fewer studies have discussed alkaline stress responses in E. coli , nonetheless two heat shock proteins and the rpoS gene have been shown to take part in the alkaline stress response (Saito and Kobayashi ; Sharma and Beuchat ), and other propositions have been put forward for other lactic acid bacteria (Nyanga‐Koumou et al ).…”