Monthly Archives: August 2019

Research – Effect of Sodium Hypochlorite on Biofilm-Forming Ability of Histamine-Producing Bacteria Isolated from Fish

Posted on August 14, 2019 by | Leave a comment

Journal of Food Protection

ABSTRACT

Histamine poisoning occurs when temperature-abused marine fish containing elevated levels of histamine are consumed. Histamine-producing bacteria found in fish can colonize processing surfaces and form biofilms. In this study, the biofilm-forming abilities of histamine-producing bacteria from Indian mackerel (Rastrelliger kanagurta) and the effect of hypochlorite treatment on biofilm formation were studied. The isolates of this study produced histamine in the range of 471 to 2,126 ppm. The histidine decarboxylase gene hdc was detected in all isolates producing histamine except in one strain each of Psychrobacter pulmonis and Proteus vulgaris. All isolates tested in this study produced moderate biofilms under control conditions, whereas exposure to 1 and 3 ppm of sodium hypochlorite significantly enhanced biofilm formation. However, exposure to 5 ppm of sodium hypochlorite showed an inhibitory effect on biofilm formation by all the isolates except Klebsiella variicola. The results of this study suggest that histamine-producing bacteria can form stable biofilms and that this activity may be enhanced by the application of low levels of sodium hypochlorite, a phenomenon that might influence the persistence of histamine-producing bacteria in fish processing areas.

HIGHLIGHTS

  • Bacteria isolated from Indian mackerel produced histamine in the range of 471 to 2,126 ppm.

  • Histamine-producing bacteria isolated from the same fish can vary in the levels of histamine produced.

  • The hdc gene was not detected in one strain each of Psychrobacter pulmonis and Proteus vulgaris.

  • All histamine-producing bacteria formed moderate biofilms under control conditions.

  • Exposure to 1 and 3 ppm of sodium hypochlorite increased biofilm formation by histamine-producing bacteria.

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Posted in Biofilm, Enterobacteriaceae, Food Micro Blog, Food Microbiology, Food Microbiology Blog, Food Spoilage, Histamine, Klebsiella, microbial contamination, Microbiology, Proteus, Uncategorized

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

Posted on August 14, 2019 by | Leave a comment

Journal of Food Protection

ABSTRACT

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.

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Posted in food bourne outbreak, food contamination, Food Inspections, Food Micro Blog, Food Microbiology, Food Microbiology Blog, Food Pathogen, Food Safety, Food Technology, Food Testing, foodborne disease, Foodborne Illness, Salmonella, Uncategorized

Research -Fate of Listeria monocytogenes in Ready-to-Eat Refrigerated Dips Treated with High Pressure Processing

Posted on August 13, 2019 by | Leave a comment

Journal of Food Protection

ABSTRACT

Various outbreaks and recalls have been associated with Listeria monocytogenes contamination of ready-to-eat (RTE) food products, including dips. High pressure processing (HPP) is useful for reducing levels of bacteria in many RTE food products, but its efficacy for reduction of pathogens in RTE dips is not well understood. In this study, laboratory-prepared hummus, tahini, baba ghanoush, guacamole, and pesto were initially treated with HPP at 350 MPa for up to 240 s to assess L. monocytogenes inactivation and determine D-values. D350 MPa-values in hummus, guacamole, and baba ghanoush were 105.3, 71.3, and 34.0 s, respectively. No significant reduction in L. monocytogenes levels was observed in tahini or pesto at 350 MPa for 240 s or after additional treatment for up to 600 s at 600 MPa (P > 0.05). Overall, the results of this study highlight the efficacy of HPP for reducing L. monocytogenes levels in certain RTE dips and but not in others.

HIGHLIGHTS

  • HPP technology was used to reduce L. monocytogenes levels in RTE dips.

  • Treatment at 350 MPa reduced the pathogen in hummus, baba ghanoush, and guacamole.

  • No reduction of L. monocytogenes was observed in tahini or pesto treated with HPP.

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Posted in Food Micro Blog, Food Microbiology Blog, Food Technology, Listeria, Listeria monocytogenes, microbial contamination, Microbiology, Uncategorized

Research – Combined Effect of Storage Condition, Surface Integrity, and Length of Shelf Life on the Growth of Listeria monocytogenes and Spoilage Microbiota on Refrigerated Ready-to-Eat Products

Posted on August 13, 2019 by | Leave a comment

Journal of Food Protection

ABSTRACT

Psychrotolerant growth of Listeria monocytogenes in ready-to-eat (RTE) foods increases the risk to food safety, particularly when spoilage does not occur prior to L. monocytogenes growth of >1 log CFU/g. The purpose of this study was to evaluate the relative rates of quality deterioration and L. monocytogenes growth in six product systems (tomatoes, apples, fresh-cut cantaloupe, fresh-cut lettuce, baby spinach, and commercially processed turkey slices) under various conditions of refrigeration temperatures, atmospheres, and quality. Cantaloupe and spinach leaves supported >1 log CFU/g growth of L. monocytogenes before product spoilage at both 4 and 9°C. In some cases, conditions that improved microbial quality by extending shelf life also allowed L. monocytogenes growth of >1 log CFU/g before deterioration due to microbial spoilage. For example, storage with modified atmosphere packaging enhanced L. monocytogenes growth relative to spoilage microbiota in lettuce leaves (1.0-log increase 7 days before spoilage). In contrast, the use of secondary quality produce (i.e., apples, tomatoes, and lettuce with physical damage) reduced shelf life and, consequently, limited the time for L. monocytogenesproliferation. Therefore, spoilage cannot be considered a fail-safe indicator or proxy for limitation of shelf life across refrigerated RTE products.

HIGHLIGHTS

  • Listeria growth that occurs before product spoilage enhances consumer risk in RTE foods.

  • Modified atmosphere packaging and surface damage enhanced Listeria growth versus spoilage.

  • Trade-offs between shelf-life extension and safety should be evaluated before eliminating date labels.

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Posted in Food Micro Blog, Food Microbiology Blog, Listeria, Listeria monocytogenes, microbial contamination, Microbiology, Uncategorized

Research – Desiccation and Thermal Resistance of Escherichia coli O121 in Wheat Flour

Posted on August 12, 2019 by | Leave a comment

Journal of Food Protection

ABSTRACT

Non-O157 Shiga toxin–producing Escherichia coli infections have recently been associated with wheat flour on two separate accounts in the United States and Canada. However, there is little information regarding the thermal resistance and longevity of non-O157 Shiga toxin–producing Escherichia coli during storage in low-moisture environments. The objectives of this study were to determine the thermal inactivation kinetics of E. coli O121 in wheat flour and to compare the thermal inactivation rates with those of other pathogens. Wheat flour, inoculated with E. coli O121, was equilibrated at 25°C to a water activity of 0.45 in a humidity-controlled conditioning chamber. Inoculated samples were treated isothermally at 70, 75, and 80°C, and posttreatment population survivor ratios were determined by plate counting. D– and z-values calculated with a log-linear model, were compared with those obtained in other studies. At 70, 75, and 80°C, the D-values for E. coli O121 were 18.16 ± 0.96, 6.47 ± 0.50, and 4.58 ± 0.40 min, respectively, and the z-value was 14.57 ± 2.21°C. Overall, E. coli O121 was observed to be slightly less thermally resistant than what has been previously reported for Salmonella Enteritidis PT30 in wheat flour as measured under the same conditions with the same methods.

HIGHLIGHTS

  • Thermal resistance of E. coli O121 in wheat flour was studied.

  • E. coli O121 exhibited greater survival upon desiccation than E. coli O157:H7.

  • E. coli O121 was slightly less thermally resistant than was previously reported for Salmonella in wheat flour.

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Posted in E.coli, E.coli O121, Food Micro Blog, Food Microbiology Blog, microbial contamination, Microbiology, STEC, Uncategorized

Research – Global Emergence of Colistin-Resistant Escherichia coli in Food Chains and Associated Food Safety Implications: A Review

Posted on August 12, 2019 by | Leave a comment

Journal of Food Protection

ABSTRACT

Antimicrobial resistance in bacteria represents one of the most important challenges for public health worldwide. Human infections from antimicrobial-resistant bacteria can be transmitted from person to person, via the environment (especially in the hospital environment), or via handling or eating contaminated foods. Colistin is well known as a last-resort antibiotic for the treatment of human infections; a recent study performed in the People’s Republic of China has revealed that colistin resistance is also conferred by the plasmid-mediated mcr-1 gene in Escherichia coli. After that discovery, further plasmid-mediated, colistin resistance genes have been detected. However, to date, only reports on E. coli carrying the mcr-1 gene (E. coli mcr-1+) in foodstuff are available. E. coli mcr-1+ has been isolated from food of animal origin and vegetables; this discovery has opened a debate among food safety experts. This review aims to provide a critical overview of the currently available scientific literature on the presence of the plasmid-mediated, colistin resistance gene E. coli mcr-1 in foodstuffs, focusing on the main implications and future perspectives for food safety.

HIGHLIGHTS

  • Antimicrobial resistance in the food chain: a One Health perspective.

  • Escherichia coli carries the mcr-1 gene in food-producing animals.

  • Escherichia coli carrying the mcr-1 gene in food from animals and vegetables is significant.

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Posted in Antibiotic Resistance, antimicrobial resistance, Antimicrobials, Colistin Resistant, E.coli, Food Micro Blog, Food Microbiology Blog, mcr-1 gene, microbial contamination, Microbiology, Uncategorized

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

Posted on August 11, 2019 by | Leave a comment

Journal of Food Protection

ABSTRACT

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.

HIGHLIGHTS

  • 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.

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Posted in Food Hygiene, Food Micro Blog, Food Microbiology Blog, Food Safety, Food Technology, Food Testing, microbial contamination, Microbiology, Salmonella, Uncategorized

Research – Antimicrobial Activity and Action Approach of the Olive Oil Polyphenol Extract Against Listeria monocytogenes

Posted on August 11, 2019 by | Leave a comment

Frontiers in Microbiology

Olive oil polyphenol extract (OOPE) has been reported to have antibacterial activity; however, its effect on Listeria monocytogenes is less studied so far. This study, thus, aimed to reveal its antimicrobial activity and action approach against L. monocytogenes via evaluating the minimum inhibitory concentration (MIC) as well as the changes of intracellular adenosine 5′-triphosphate (ATP) concentration, cell membrane potential, bacterial protein, DNA, and cell morphology. The results showed that OOPE could inhibit the growth of L. monocytogeneswith a measured MIC of 1.25 mg/ml. L. monocytogenes cells treated by OOPE showed significant reduction in intracellular ATP concentrations, bacterial protein, or DNA (p < 0.05), in comparison with those without any treatment. In addition, OOPE was observed to depolarize strain cells and alter cell morphology, resulting in damaged cell membrane and, thereby, leakage of cell fluid. These findings demonstrated that OOPE had inhibition on L. monocytogenes via its action on cells, suggesting its potential as a natural preservative.

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Posted in Food Micro Blog, Food Microbiology Blog, Food Pathogen, Food Technology, Listeria, Listeria monocytogenes, microbial contamination, Microbiology, pathogenic, Technology, Uncategorized

Research – Bacteria-killing gel heals itself while healing you

Posted on August 10, 2019 by | Leave a comment

Science Daily

McMaster researchers have developed a novel new gel made entirely from bacteria-killing viruses.

The anti-bacterial gel, which can be targeted to attack specific forms of bacteria, holds promise for numerous beneficial applications in medicine and environmental protection.

Among many possibilities, it could be used as an antibacterial coating for implants and artificial joints, as a sterile growth scaffold for human tissue, or in environmental cleanup operations, says chemical engineer Zeinab Hosseini-Doust.

Her lab, which specializes in developing engineering solutions for infectious disease, grew, extracted and packed together so many of the viruses — called bacteriophages, or simply phages — that they assembled themselves spontaneously into liquid crystals and, with the help of a chemical binder, formed into a gelatin-like substance that can heal itself when cut.

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Posted in bacterial contamination, Bacterial Infections, Bacteriophage, Food Micro Blog, Food Microbiology Blog, Microbiology, Research, Uncategorized, Virus

Research – Conditions at the time of inoculation influence survival of attenuated Escherichia coli O157:H7 on field-inoculated lettuce

Posted on August 9, 2019 by | Leave a comment

Science Direct

Highlights

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Higher percentages of E. coli–positive plants recovered when inoculation was closer to harvest.

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Higher relative humidity and leaf surface wetness were measured during night inoculation.

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Short-term smaller initial population declines were observed after night inoculation.

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E. coli population sizes were similar 2 or more days after night or day inoculation.

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Probability of detecting E. coli was higher for longer times when inoculated at higher levels.

Abstract

The impact of plant development, environmental conditions at the time of inoculation, and inoculum concentration on survival of attenuated BSL1 Escherichia coli O157:H7 strain ATCC 700728 on field-grown romaine lettuce was evaluated over 3 years. E. coli 700728 was inoculated onto 4- and 6-week-old romaine lettuce plants in the Salinas Valley, CA, at night or the next morning with either low (5 log) or high (7 log) cell numbers per plant to simulate a single aqueous contamination event. At night, when leaf wetness and humidity levels were high, E. coli cell numbers declined by 0.5 log CFU/plant over the first 8–10 h. When applied in the morning, E. coli populations declined up to 2 log CFU/plant within 2 h. However, similar numbers of E. coli were retrieved from lettuce plants at 2 and 7 days. E. coli cell numbers per plant were significantly lower (P < 0.05) 7 days after application onto 4-week-old compared to 6-week-old plants. E. coli 700728 could be recovered by plating or enrichment from a greater proportion of plants for longer times when inoculated at high compared with low initial concentrations and after inoculation of 6-week-old plants compared with 4-week-old plants, even at the low initial inoculum. A contamination event near harvest or when leaf wetness and humidity levels are high may enhance survivability, even when low numbers of E. coli are introduced.

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Posted in E.coli, E.coli O157, E.coli O157:H7, food contamination, Food Hygiene, Food Inspections, Food Micro Blog, Food Microbiology, Food Microbiology Blog, Food Pathogen, Food Poisoning, Food Safety, Food Technology, Food Testing, Uncategorized