Category Archives: Microbiology

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

Posted on August 17, 2019 by | Leave a comment

Journal of Food Protection

ABSTRACT

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.

HIGHLIGHTS

  • 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.

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

Research – Occurrence of Escherichia coli O157:H7 in Pest Flies Captured in Leafy Greens Plots Grown Near a Beef Cattle Feedlot

Posted on August 16, 2019 by | Leave a comment

Journal of Food Protection

ABSTRACT

Leafy greens are leading vehicles for Escherichia coli O157:H7 foodborne illness. Pest flies can harbor this pathogen and may disseminate it to produce. We determined the occurrence of E. coli O157:H7–positive flies in leafy greens planted up to 180 m from a cattle feedlot and assessed their relative risk to transmit this pathogen to leafy greens. The primary fly groups captured on sticky traps at the feedlot and leafy greens plots included house flies (Musca domestica L.), face flies (Musca autumnalisL.), stable flies (Stomoxys calcitrans L.), flesh flies (family Sarcophagidae), and blow flies (family Calliphoridae). E. coliO157:H7 carriage rates of house, face, flesh, and blow flies were similar (P > 0.05), ranging from 22.3 to 29.0 flies per 1,000 flies. In contrast, the carriage rate of stable flies was lower at 1.1 flies per 1,000 flies (P < 0.05). Differences in carriage rates are likely due to the uses of fresh bovine feces and manure by these different pest fly groups. E. coli O157:H7 carriage rates of total flies did not differ (P > 0.05) by distance (ranging from 0 to 180 m) from the feedlot. Most fly isolates were the same predominant pulsed-field gel electrophoresis types found in feedlot surface manure and leafy greens, suggesting a possible role for flies in transmitting E. coli O157:H7 to the leafy greens. However, further research is needed to clarify this role and to determine set-back distances between cattle production facilities and produce crops that will reduce the risk for pathogen contamination by challenging mechanisms like flies.

HIGHLIGHTS

  • E. coli O157:H7 was common in flies captured in leafy greens plots near a feedlot.

  • E. coli O157:H7 carriage rates of house, face, flesh, and blow flies were similar.

  • Stable flies had lower E. coli O157:H7 carriage than the other four fly groups.

  • E. coli O157:H7 carriage of total flies was not affected by distance up to 180 m.

  • Research is needed to determine risk for leafy green contamination by pest flies.

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Posted in E.coli, E.coli O157, E.coli O157:H7, Food Illness, Food Micro Blog, Food Microbiology Blog, Foodborne Illness, Illness, microbial contamination, Microbiology, Uncategorized

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

Posted on August 16, 2019 by | Leave a comment

Science Direct

Highlights

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

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

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

Abstract

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.

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Posted in E.coli, E.coli O157, E.coli O157:H7, Food Micro Blog, Food Microbiology, Food Microbiology Blog, Food Technology, Listeria, Listeria monocytogenes, microbial contamination, Microbiology, Salmonella, Technology, Uncategorized

Research – Domestic Kitchen Microbiological Contamination and Self-Reported Food Hygiene Practices of Older Adult Consumers

Posted on August 15, 2019 by | Leave a comment

Journal of Food Protection

ABSTRACT

Because of increased susceptibility, older adults have an increased risk of foodborne infection, and data suggest elevated incidence; therefore, food hygiene is essential to reduce the risk. Research suggests older adults’ inadequate knowledge and negative attitudes toward food hygiene may increase implementation of unsafe food practices. Data on microbiological contamination of domestic kitchens of older adults are lacking. Therefore, this study aimed to determine microbiological contamination of domestic kitchens of older adults. Food contact surfaces and equipment (n = 1,292) in domestic kitchens (n = 100) of older adults (≥60 years) were analyzed to isolate aerobic bacteria, Enterobacteriaceae, Staphylococcus aureus, and Listeria spp.; self-reported hygiene practices were also recorded. Highest contamination levels were determined on in-use cleaning equipment (dish brushes, dishcloths, sponges) with aerobic bacteria <9.3 log CFU per item, Enterobacteriaceae <8.8 log CFU per item, and S. aureus <7.0 log CFU per item. Reported usage length of dish brushes was significantly correlated (P< 0.05) with Enterobacteriaceae contamination. Significant correlations (P < 0.05) were determined between contamination and reported cleaning frequency of refrigerators. Contamination of hand towels in single-occupant households was significantly greater (P < 0.05) than in multioccupant households. The study facilitates novel comparison between reported hygiene practices with microbial contamination, suggesting older adults fail to implement adequate and regular hygiene practices that may increase the possibility of cross-contamination in the domestic kitchen and the associated risk of foodborne illness. Data from this study have determined a need for older adults to improve food hygiene practices in the domestic kitchen.

HIGHLIGHTS

  • In-use dish brushes and dishcloths were most commonly contaminated with high counts of bacteria.

  • Correlations existed between dishcloth contamination and multiple kitchen sites.

  • Reported dish brush usage length was significantly correlated with contamination level.

  • Reported time since cleaning of refrigerators was positively correlated with contamination levels.

  • Inadequate and irregular hygiene practices may increase foodborne illness risk to older adults.

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Posted in Enterobacteriaceae, Food Illness, Food Micro Blog, Food Microbiology Blog, Foodborne Illness, Illness, Listeria, Listeria monocytogenes, listeriosis, microbial contamination, Microbiology, Staphylococcus aureus, Uncategorized

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 -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