Category Archives: Uncategorized

Research – Preliminary Assessment of Visible, Near-Infrared, and Short-Wavelength–Infrared Spectroscopy with a Portable Instrument for the Detection of Staphylococcus aureus Biofilms on Surfaces

Journal of Food Protection

ABSTRACT

Bacterial biofilms constitute a major source of sanitary problems and economic losses in the food industry. Indeed, biofilm removal may require intense mechanical cleaning procedures or very high concentrations of disinfectants or both, which can be damaging to the environment and human health. This study assessed the efficacy of a technique based on spectroscopy in the visible, near-infrared, and short-wavelength infrared range for the quick detection of biofilms formed on polystyrene by the pathogenic bacterium Staphylococcus aureus. To do that, biofilms corresponding to three S. aureus strains, which differed in biofilm-forming ability and composition of the extracellular matrix, were allowed to develop for 5 or 24 h, representing an active formation stage and mature biofilms, respectively. Spectral analysis of the samples, corresponding to three biological replicates of each condition, was then performed by using a portable device. The results of these experiments showed that partial least-squares discriminant analysis of the spectral profile could discriminate between surfaces containing attached bacterial biomass and noninoculated ones. In this model, the two first principal components accounted for 39 and 19% of the variance and the estimated error rate stabilized after four components. Cross-validation accuracy of this assessment was 100%. This work lays the foundation for subsequent development of a spectroscopy-based protocol that allows biofilm detection on food industrial surfaces.

HIGHLIGHTS
  • A biofilm detection spectroscopy–based technique with a portable device was tested.

  • Staphylococcus aureus biofilms of different strengths were scanned with the device.

  • Spectral data showed correlation with crystal violet staining quantification results.

  • Data from spectral analysis was suitable for prediction of biofilm contamination.

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

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.

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

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.

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

Science Direct

Highlights

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.

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.

Research – Whole Genome Sequencing Characterization of Shiga Toxin–Producing Escherichia coli Isolated from Flour from Swiss Retail Markets

Journal of Food Protection

ABSTRACT

Shiga toxin–producing Escherichia coli (STEC) strains are often found in food and cause human infections. Although STEC O157:H7 is most often responsible for human disease, various non-O157 subtypes have caused individual human infections or outbreaks. The importance of STEC serogroup typing is decreasing while detection of virulence gene patterns has become more relevant. Whole genome sequencing (WGS) reveals the entire spectrum of pathogen information, such as toxin variant, serotype, sequence type, and virulence factors. Flour has not been considered as a vector for STEC; however, this product has been associated with several STEC outbreaks in the last decade. Flour is a natural product, and milling does not include a germ-reducing step. Flour is rarely eaten raw, but the risks associated with the consumption of unbaked dough are probably underestimated. The aim of this study was to determine the prevalence of STEC in flour samples (n = 93) collected from Swiss markets and to fully characterize the isolates by PCR assay and WGS. The prevalence of STEC in these flour samples was 10.8% as indicated by PCR, and a total of 10 STEC strains were isolated (two flour samples were positive for two STEC subtypes). We found one stx2-positve STEC isolate belonging to the classic serogroups frequently associated with outbreaks that could potentially cause severe disease. However, we also found several other common or less common STEC subtypes with diverse virulence patterns. Our results reveal the benefits of WGS as a characterization tool and that flour is a potentially and probably underestimated source for STEC infections in humans.

HIGHLIGHTS
  • Several STEC serotypes, including O26, were isolated from 8 (8.6%) of 93 flour samples.

  • STEC isolates from flour had a variety of virulence patterns.

  • Flour is a probably underestimated source of STEC infections in humans.

  • WGS for STEC characterization is more comprehensive than common serotyping.

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

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.

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

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.

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

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.

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

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.

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

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.