Category Archives: Salmonella

USA – FDA Sampling of Romaine Lettuce in Yuma Finds No Widespread STEC or Salmonella Contamination

Food Safety Tech

Following last year’s widespread E.coli O157 outbreak involving romaine lettuce linked to the Yuma, Arizona growing region (Spring 2018), FDA launched a sampling assignment to test romaine lettuce for pathogenic Shiga toxin-producing Escherichia coli (STEC) and Salmonella spp. The microbiological surveillance samplingbegan on December 18, 2018 in the Yuma region and focused on 26 commercial coolers and cold storage facilities to allow FDA to sample multiple farms from several locations at once. The agency collected and tested a total of 188 samples for both pathogens. It did not detect Salmonella in any sample; STEC was detected in one sample, but additional analysis found that the bacteria was not pathogenic.

“The findings of this assignment suggest that there was no widespread Salmonella or STEC contamination of romaine lettuce from the Yuma growing region during the period when sampling occurred. As a next step, the FDA is working with leafy green stakeholders in the Yuma region to consider a longer-term environmental study to identify and control risks that will prevent future outbreaks, with the ultimate goal of protecting consumers. – FDA

The point of the sampling assignment was to determine whether target pathogens were present, and if so, to respond quickly before contaminated products reached consumers.

USA – More pig ear dog treats recalled in multistate outbreak

Food Safety News

Dog Goods USA LLC of Tobyhanna, PA joins the list of companies involved in a federal and state investigation regarding contaminated pig ear dog treats that are likely responsible for a multistate, multidrug-resistant Salmonella outbreak. 

Dog Goods USA LLC has recalled its Chef Toby Pig Ears Treats because they have the potential to be contaminated with Salmonella, according to a notice posted by the Food and Drug Administration. The Centers for Disease Control and Prevention is working with the FDA and several state agencies on the outbreak investigation.

According to the recall notice, the affected product includes non-irradiated bulk and packaged pig ears branded Chef Toby Pig Ears, due to potential Salmonella contamination.

Research – High-Intensity Light Pulses To Inactivate Salmonella Typhimurium on Mexican Chia (Salvia hispanica L.) Seeds

Journal of Food Protection


Chia seeds provide a suitable environment for microorganisms. However, it is difficult to disinfect these seeds with water and/or chemical disinfectant solutions because the mucilage in the seeds can absorb water and consequently form gels. High-intensity light pulses (HILP) is one of the most promising emerging technologies for inactivating microorganisms on surfaces, in clear liquids and beverages, and on solid foods. The aim of this work was to evaluate the effect of HILP on SalmonellaTyphimurium in culture medium (in vitro tests) and inoculated onto chia seeds (in vivo tests). HILP was effective against Salmonella Typhimurium under both conditions: 8 s of treatment (10.32 J/cm2) resulted in a 9-log reduction during in vitro tests, and 15 s of treatment (19.35 J/cm2) resulted in a 4-log reduction on the inoculated chia seeds. Salmonella Typhimurium inactivation kinetics were accurately described using the Weibull model (R2 > 0.939). These results indicate that the use of HILP for microbial inactivation on seeds could generate products suitable for human consumption.

  • Decontamination of chia seeds is complex because of rapid formation of gel on the seeds.

  • HILP was effective against Salmonella Typhimurium in vitro and on chia seeds.

  • The Weibull model appropriately described Salmonella Typhimurium inactivation curves.

  • HILP is a promising emerging technology for eliminating pathogens from chia seeds.

Research – Ultrasound treatment combined with fumaric acid for inactivating food-borne pathogens in apple juice and its mechanisms

Science Direct


The combination of Ultrasound (US) and fumaric acid (FA) showed a synergistic bactericidal effect in apple juice.

US-FA combined treatment of apple juice did not affect quality.

Cell membrane damage was the main mechanism of US-FA synergistic lethal effect.


The purpose of this study was to evaluate the synergistic bactericidal efficacy of combining ultrasound (US) and fumaric acid (FA) treatment against Escherichia coliO157:H7, Salmonella Typhimurium, and Listeria monocytogenes in apple juice and to identify the synergistic bactericidal mechanisms. Additionally, the effect of combination treatment on juice quality was determined by measuring the changes in color, pH, non-enzymatic browning index, and total phenolic content. A mixed cocktail of the three pathogens was inoculated into apple juice, followed by treatment with US (40 kHz) alone, FA (0.05, 0.1, and 0.15%) alone, and a combination of US and FA for 1, 2, 3, 4, and 5 min. Combined US and 0.15% FA treatment for 5 min achieved 5.67, 6.35, and 3.47 log reductions in E. coli O157:H7, S.Typhimurium, and L. monocytogenes, respectively, with the 1.55, 2.37, and 0.57 log CFU reductions attributed to the synergistic effect. Although the pH value slightly decreased as FA increased, there were no significant (P > 0.05) differences in color values, browning indices, and phenolic content between untreated and treated samples. To identify the mechanism of this synergistic bactericidal action, membrane integrity, malfunctions in the membrane efflux pump, and intracellular enzyme activity were measured. The analyses confirmed that damage to the cell envelope (membrane integrity and efflux pump) was strongly related to the synergistic microbial inactivation. These results suggest that simultaneous application of US treatment and FA is a novel method for ensuring the microbial safety of apple juice.

Research – A Bacteriophage Cocktail Eliminates Salmonella Typhimurium from the Human Colonic Microbiome while Preserving Cytokine Signaling and Preventing Attachment to and Invasion of Human Cells by Salmonella In Vitro

Journal of Food Protection


Nontyphoidal Salmonella strains continue to be a major cause of foodborne illness globally. One intriguing approach to reducing the risk of salmonellosis is the direct ingestion of phages targeting Salmonella to enhance natural gut resilience and provide protection during foodborne disease outbreaks. We evaluated the ability of a prophylactically administered bacteriophage cocktail, the foodborne outbreak pill (FOP) targeting Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella, to resolve a Salmonella infection in the Simulator of the Human Intestinal Microbial Ecosystem (SHIME), a simulated gut platform populated by the human intestinal microbiome of healthy donors. The FOP preparation eliminated Salmonella enterica serovar Typhimurium from the colon compartment of the SHIME platform but health-associated metabolites, such as short-chain fatty acids and lactate, remained stable or increased in a donor-dependent manner. In studies of human intestinal cells, pretreatment of Salmonella Typhimurium with the FOP cocktail preserved lipopolysaccharide-stimulated signaling in a Caco-2–THP-1 Transwell system and prevented destruction of the Caco-2 monolayer by Salmonella. Adhesion and invasion of intestinal epithelial cells by Salmonella—a critical factor in Salmonella pathogenesis—was blunted when the bacteria were incubated with the FOP preparation before addition to the monolayer. The FOP phage cocktail was effective for (i) eliminating Salmonella from a simulated human gut without disturbing the indigenous microbiota and (ii) reducing the risk of invasion by Salmonella into the intestinal epithelia. These results suggest that the FOP preparation may be of value for reducing the risk of salmonellosis in humans, e.g., during foodborne disease outbreaks.

Research – Effect of Food Structure, Water Activity, and Long-Term Storage on X-Ray Irradiation for Inactivating Salmonella Enteritidis PT30 in Low-Moisture Foods

Journal of Food Protection


Recent outbreaks and recalls of low-moisture foods contaminated with Salmonella have been recognized as a major public health risk that demands the development of new Salmonella mitigation strategies and technologies. This study aimed to assess the efficacy of X-ray irradiation for inactivating Salmonella on or in almonds (kernels, meal, butter), dates (whole fruit, paste), and wheat (kernels, flour) at various water activities (aw) and storage periods. The raw materials were inoculated with Salmonella Enteritidis PT30, conditioned to 0.25, 0.45, and 0.65 aw in a humidity-controlled chamber, processed to various fabricated products, and reconditioned to the desired aw before treatment. In a storage study, inoculated almond kernels were stored in sealed tin cans for 7, 15, 27, and 103 weeks, irradiated with X ray (0.5 to 11 kGy, targeting up to a ∼2.5-log reduction) at the end of each storage period, and plated for Salmonella survivors to determine the efficacy of irradiation in terms of D10-value (dose required to reduce 90% of the population). Salmonella was least resistant (D10-value = 0.378 kGy) on the surface of almond kernels at 0.25 aw and most resistant (D10-value = 2.34 kGy) on the surface of dates at 0.45 aw. The Salmonella D10-value was 61% lower in date paste than on whole date fruit. Storage of almonds generally had no effect on the irradiation resistance of Salmonella over 103 weeks. Overall, these results indicate that product structure (whole, meals, powder, or paste), water activity (0.25 to 0.65 aw), and storage period (0 to 103 weeks) should be considered when determining the efficacy of X-ray irradiation for inactivating Salmonella in various low-water-activity foods.

  • Salmonella resistance to X ray was significantly different on almonds, wheat, and dates.

  • The structural changes of almonds significantly impacted Salmonella resistance to X ray.

  • Water activity affected the efficacy of X ray for inactivating Salmonella in low-moisture foods.

  • Storing almonds up to 103 weeks had no effect on the X-ray resistance of Salmonella.

Research -Slow growth determines nonheritable antibiotic resistance in Salmonella enterica

Science Mag

kswfoodworld Salmonella

Image CDC

Slow growth for bacterial persistence

Even bacteria that do not carry mutations or genes that confer resistance to specific antibiotics can survive antibiotic treatment, a phenomenon known as persistence (see the Focus by Kaldalu and Tenson). Several models have been proposed to account for bacterial persistence, including the activation of toxins in toxin-antitoxin modules, the production of the alarmone guanosine (penta) tetraphosphate [(p)ppGpp], and a reduction in intracellular adenosine triphosphate (ATP) abundance. Pontes and Groisman demonstrated that Salmonella exhibited persistence even in the absence of toxin-antitoxin modules or (p)ppGpp production and under conditions that increased intracellular ATP. These and additional findings show that slow growth alone is sufficient for persistence and may contribute to the difficulty in treating some bacterial infections.


Bacteria can withstand killing by bactericidal antibiotics through phenotypic changes mediated by their preexisting genetic repertoire. These changes can be exhibited transiently by a large fraction of the bacterial population, giving rise to tolerance, or displayed by a small subpopulation, giving rise to persistence. Apart from undermining the use of antibiotics, tolerant and persistent bacteria foster the emergence of antibiotic-resistant mutants. Persister formation has been attributed to alterations in the abundance of particular proteins, metabolites, and signaling molecules, including toxin-antitoxin modules, adenosine triphosphate, and guanosine (penta) tetraphosphate, respectively. Here, we report that persistent bacteria form as a result of slow growth alone, despite opposite changes in the abundance of such proteins, metabolites, and signaling molecules. Our findings argue that transitory disturbances to core activities, which are often linked to cell growth, promote a persister state regardless of the underlying physiological process responsible for the change in growth.