Combined effects of organic acids and salt depending on type of acids and pathogens in laboratory media and acidified pickle

Salt can antagonize the lethal effect of weak organic acids against Escherichia coli O157:H7 inoculated in laboratory culture media and acidic/acidified foods

From the last several decades, previous studies have found that salt can increase the resistance of Gram-negative human-pathogenic bacteria to acidic environments in the presence of weak organic acids (OAAs), significantly increasing or extending the survival of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, Shigella sp., and Cronobacter sp., particularly in acidified foods. These pathogenic bacteria may be inclined to be less reduced after washing or dipping in weak OAAs combined with salt, thereby posing a potential food safety hazard. Particularly, it can be plausible that E. coli has varied and different mechanisms to cope with the detrimental effects imposed by weak OAAs with one carboxyl functional group by the addition of ionic or nonionic solutes, including salt, KCl, sucrose, glutamate, and fructose. Nevertheless, little is known about the intracellular physiological response of Gram-negative bacteria subjected to a simultaneous challenge with weak OAAs and salt, as well as the underlying principles of an antagonistic phenomenon (protection) affordable to E. coli by the combined treatments. Therefore, the objectives of this review are to introduce the current propensity of individual or combined treatments with weak OAAs and salt for inactivating food-borne pathogens, to compile a selected area of studies focusing on the antagonistic interaction between short-chained weak OAAs and salt for inhibiting or eliminating Gram-negative bacteria, and then to uncover the putative mechanisms mediating the improved resistance of E. coli O157:H7 to weak acids by the salt amendment.

Traditional uses, phytochemistry, pharmacology, toxicity and clinical application of traditional Chinese medicine Cynoglossum amabile: a review

Cynoglossum amabile, a member of the Boraginaceae family, is a well-known traditional Chinese medicine and ethnomedicine known as Daotihu. Despite several studies confirming the presence of bioactive pyrrolizidine alkaloids such as amabiline, ambelline, echinatine, europine, and others in C. amabile, there has been no comprehensive review of its traditional uses, phytochemistry, and pharmacology thus far. This review was conducted by thoroughly examining the literature and analyzing network databases. It covers various aspects of C. amabile, including botanical characteristics, geographical distribution, traditional applications, phytochemistry, pharmacological activities, toxicology, and clinical applications. The results have shown that C. amabile has been traditionally used for medicinal, edible, and ornamental purposes in China for many centuries. The whole plant, root, and leaf of C. amabile are used by different ethnic groups, such as Lisu, Bai, Naxi, Yi, Jinuo, and Han, to treat malaria, hepatitis, dysentery, leucorrhea, tuberculosis cough, fracture, joint dislocation, trauma bleeding, and skin carbuncle abscess. A total of 47 chemical components, including alkaloids (pyrrolizidine alkaloids, PAs), sterols, organic acids, and saccharides, were isolated from C. amabile. Pharmacological studies show that the chemical extracts of C. amabile possess various biological activities, such as anti-inflammatory, anti-tumor, anti-microbial, cardiovascular effects, ganglionic action, and acetylcholinesterase inhibition. However, it is important to note that C. amabile exhibits hepatotoxicity, with its toxicity being linked to its primary PAs components. Although preliminary studies suggest potential applications in the treatment of prostate diseases and alopecia, further research is needed to validate these clinical uses. Our review highlights the traditional uses, phytochemistry, biological activity, toxicity, and clinical applications of C. amabile. It emphasizes the essential guiding role of the indigenous medicinal knowledge system in developing new drugs. Previous studies have shown that the phytochemical and pharmacological characteristics of C. amabile are significantly related to its traditional medicinal practices. Cynoglossum amabile has excellent market potential and can be further analyzed in terms of phytochemistry, pharmacology, and toxicology, which are critical for its clinical drug safety, quality evaluation, and resource development.

Escherichia coli O157:H7 had a high degree of acid resistance in the presence of osmolytes (glycerol, glycine or fructose) by altering its lipid membrane composition

This study aims to investigate the resistance of E. coli O157:H7 to acetic acid (AA) or malic acid (MA) by adding osmolytes, such as glycerol, glycine, glucose, and fructose, in Luria-Bertani broth without NaCl (LBW/S) or phosphate buffer (PB) stored at 25 °C. In LBW/S, a significantly (p < 0.05) higher D-value of E. coli O157:H7 was observed when treated with AA and 20% glycine (D-value: 1.18-3.44) or 40% glucose (D-value: 1.05-2.52) compared to that of AA alone (D-value: 0.40-0.47). In contrast, the addition of osmolytes (i.e. 3-40% glucose, 3-40% fructose or 20% glycine) to LBW/S acidified by MA significantly decreased D-values of E. coli O157:H7, which was enumerated by using a selective medium. Furthermore, when E. coli O157:H7 was incubated in LBW/S containing AA and osmolytes at 25 °C for 3 d, this bacterium had an increased proportion of C16:0 and C17:0 cyclo (cyclopropane acid) compared to its AA-treated counterparts. Along with the altered shift in membrane phospholipids, the addition of osmolytes into a laboratory medium in the presence of nutritive substrates may increase the resistance of E. coli O157:H7 to AA.

The effect of manganese and iron on mediating resuscitation of lactic acid-injured Escherichia coli

Lactic acid can induce sublethal injury of E. coli through oxidative stress. In this study, we investigated changes in SOD activity, CAT activity, GSH production and ROS production during sublethal injury and resuscitation of E. coli. Then, the effect of manganese and iron during resuscitation were studied. Both cations (≥1 mmol l^-1 ) significantly promoted the resuscitation of sublethally injured E. coli induced by lactic acid and shortened the repair time (P < 0·05). Conversely, addition of N,N,N',N'-tetrakis (2-pyridylmethyl) which is a metal chelator extended the repair time. Compared with minA, manganese and iron significantly improved SOD activity at 40, 80 and 120 min and decreased ROS production at 40 and 80 min, thereby recovering injured E. coli quickly (P < 0·05). The deletion of sodA encoding Mn-SOD, sodB encoding Fe-SOD or gshA/gshB encoding GSH significantly strengthened sublethal injury and extended the repair time (P < 0·05). It meant these genes-related oxidative stress played important roles in the acid resistance of E. coli and recovery of sublethal injury. Therefore, manganese and iron can promote the recovery of lactic-injured E. coli by the way of increasing SOD activity, scavenging ROS, and relieving oxidative stress.

Inactivation of Listeria monocytogenes and Salmonella spp. in Milano-Type Salami Made with Alternative Formulations to the Use of Synthetic Nitrates/Nitrites

During the manufacture of Italian salami, a traditional meat product, a sequence of hurdles like meat fermentation, air-drying, and long ripening processes are generally sufficient to inhibit the growth of most pathogens. Furthermore, Italian salami are traditionally produced by adding synthetic nitrates/nitrites to raw meat with safety and technological aims, even if controversial opinions about their use still remain, particularly in relation to the consumer demand for natural food products. In this context, the aim of the study was to investigate the inactivation of Listeria monocytogenes and Salmonella spp. during the manufacturing process of Milano-type salami made with different formulations to evaluate the contribution of the hurdles and the vegetable or synthetic additives on the inactivation of pathogens. Thus, a challenge study was performed dividing ca. 400 kg of Milano-type salami batter into three batches: Batch (A) without nitrates/nitrites; Batch (B) with vegetable nitrates, and Batch (C) with synthetic nitrates/nitrites. The batches were separately inoculated with L. monocytogenes and Salmonella spp. and the pathogens’ survival was evaluated during the fermentation, draining, and 70-day ripening of the Milano-type salami. The pathogen counts decreased in all tested conditions, even though the highest inactivation of L. monocytogenes and Salmonella spp. (p < 0.05) was observed when nitrates or nitrites were added to the batter. This study shows how the safety of these products cannot exclude the aspect of the hurdle technology during the process, which plays a major role in the reduction of pathogens, but additives like nitrates and nitrites allow for a greater margin of safety. Thus, further studies are needed to validate the use of natural compounds as alternatives to conventional preservatives in meat products. These results may provide new information to support food business operators in producing traditional foods with alternative preservatives and competent authorities in verifying the safety of the products made with natural compounds, and to control the process parameters responsible for the synergistic effect against pathogens such as L. monocytogenes and Salmonella spp.

Cross-Talk between Probiotic Nissle 1917 and Human Colonic Epithelium Affects the Metabolite Composition and Demonstrates Host Antibacterial Effect

Colonic epithelium-commensal interactions play a very important role in human health and disease development. Colonic mucus serves as an ecologic niche for a myriad of commensals and provides a physical barrier between the epithelium and luminal content, suggesting that communication between the host and microbes occurs mainly by soluble factors. However, the composition of epithelia-derived metabolites and how the commensal flora influences them is less characterized. Here, we used mucus-producing human adult stem cell-derived colonoid monolayers exposed apically to probiotic E. coli strain Nissle 1917 to characterize the host-microbial communication via small molecules. We measured the metabolites in the media from host and bacterial monocultures and from bacteria-colonoid co-cultures. We found that colonoids secrete amino acids, organic acids, nucleosides, and polyamines, apically and basolaterally. The metabolites from host-bacteria co-cultures markedly differ from those of host cells grown alone or bacteria grown alone. Nissle 1917 affects the composition of apical and basolateral metabolites. Importantly, spermine, secreted apically by colonoids, shows antibacterial properties, and inhibits the growth of several bacterial strains. Our data demonstrate the existence of a cross-talk between luminal bacteria and human intestinal epithelium via metabolites, which might affect the numbers of physiologic processes including the composition of commensal flora via bactericidal effects.

Salt, glucose, glycine, and sucrose protect Escherichia coli O157:H7 against acid treatment in laboratory media

This study investigated the effects of combinations of acetic or malic acid and various solutes (salt, glucose, glycine, or sucrose) on the survival of Escherichia coli O157:H7 in laboratory broth. Additionally, the effectiveness of combining organic acids and various concentrations of salt (0-18%) or sucrose (0-100%) with different water activity values against E. coli O157:H7 were evaluated. For treatment of 1% malic acid, the addition of 3% salt showed synergistic effect. Whereas, when 3% salt, glucose, glycine, or sucrose was added to 1% acetic acid, the solutes antagonized the action of the acid against E. coli O157:H7. Acetic, lactic, or propionic acid combined with salt at either 7 or 9% or sucrose at 60, 80, or 100% resulted in the highest resistance of E. coli O157:H7. From a result of evaluating the membrane fatty acid (MFA) composition of cells, salt or sucrose significantly increased levels of saturated fatty acids (SFAs) or SFAs and cyclopropane fatty acids, respectively. From the results of this study, the addition of solutes and organic compounds may increase the tolerance of E. coli O157:H7 to acetic, lactic, and propionic acid treatments and that the salt or sucrose significantly affects cell MFA composition.

High concentration of sodium chloride could induce the viable and culturable states of Escherichia coli O157:H7 and Salmonella enterica serovar Enteritidis

In the present study, Escherichia coli O157:H7 and Salmonella enterica serovar Enteritidis were transferred into Luria-Bertani medium without NaCl (LBWS) and adjusted to various pHs (4, 5, 6 and 7) with lactic acid containing 0·75, 5, 10 and 30% NaCl, and stored at 25°C until the bacterial populations reached below detectable levels on tryptic soy agar (TSA). Although E. coli O157:H7 and S. Enteritidis did not grow on TSA when incubated in LBWS with 30% NaCl for 35 and 7 days, more than 60 and 70% of the bacterial cells were shown to be viable via fluorescent staining with SYTO9 and propidium iodide (PI), respectively, suggesting that a number of cells could be induced into the viable but nonculturable (VBNC) state. These bacteria that were induced into a VBNC state were transferred to a newly prepared tryptic soy broth (TSB) and then incubated at 37°C for several days. After more than 7 days, E. coli O157:H7 and S. Enteritidis regained their culturability. We, therefore, suggest that E. coli O157:H7 and S. Enteritidis entered the VBNC state under the adverse condition of higher salt concentrations and were revived when these conditions were reversed.

Effects of Sodium Chloride or Calcium Chloride Concentration on the Growth and Survival of Escherichia coli O157:H7 in Model Vegetable Fermentations

HIGHLIGHTS

NaCl and CaCl₂ concentrations affected LAB and STEC strains differently. Growth rates at 6% NaCl were reduced for STEC more than LAB in vegetable broth. Extent of growth was reduced for STEC versus LAB for most vegetable fermentations. Death rates were minimally affected by salt type or concentration with lactic acid. Correlations between salt and STEC die-off were inconsistent for fermentation.

Enhanced Antimicrobial Activity Based on a Synergistic Combination of Sublethal Levels of Stresses Induced by UV-A Light and Organic Acids

The reduction of microbial load in food and water systems is critical for their safety and shelf life. Conventionally, physical processes such as heat or light are used for the rapid inactivation of microbes, while natural compounds such as lactic acid may be used as preservatives after the initial physical process. This study demonstrates the enhanced and rapid inactivation of bacteria based on a synergistic combination of sublethal levels of stresses induced by UV-A light and two food-grade organic acids. A reduction of 4.7 ± 0.5 log CFU/ml in Escherichia coli O157:H7 was observed using a synergistic combination of UV-A light, gallic acid (GA), and lactic acid (LA), while the individual treatments and the combination of individual organic acids with UV-A light resulted in a reduction of less than 1 log CFU/ml. Enhanced inactivation of bacteria on the surfaces of lettuce and spinach leaves was also observed based on the synergistic combination. Mechanistic investigations suggested that the treatment with a synergistic combination of GA plus LA plus UV-A (GA+LA+UV-A) resulted in significant increases in membrane permeability and intracellular thiol oxidation and affected the metabolic machinery of E. coli In addition, the antimicrobial activity of the synergistic combination of GA+LA+UV-A was effective only against metabolically active E. coli O157:H7. In summary, this study illustrates the potential of simultaneously using a combination of sublethal concentrations of natural antimicrobials and a low level of physical stress in the form of UV-A light to inactivate bacteria in water and food systems.IMPORTANCE There is a critical unmet need to improve the microbial safety of the food supply, while retaining optimal nutritional and sensory properties of food. Furthermore, there is a need to develop novel technologies that can reduce the impact of food processing operations on energy and water resources. Conventionally, physical processes such as heat and light are used for inactivating microbes in food products, but these processes often significantly reduce the sensory and nutritional properties of food and are highly energy intensive. This study demonstrates that the combination of two natural food-grade antimicrobial agents with a sublethal level of physical stress in the form of UV-A light can greatly increase microbial load inactivation. In addition, this report elucidates the potential mechanisms for this synergistic interaction among physical and chemical stresses. Overall, these results provide a novel approach to develop antimicrobial solutions for food and water systems.