Nuts and Grains: Microbiology and Preharvest Contamination Risks

U.S. Consumers' Tree Nut Food Safety Knowledge, Perceptions, and Handling Practices across Demographic Groups

Tree nuts are often perceived as presenting a low risk for foodborne illness, despite their association with several foodborne outbreaks and recalls in recent years. An online survey was designed to assess how consumers' food safety knowledge, perception of risks and benefits, and preferred sources for food safety information influence their tree nut handling behavior. Participants (n = 981) who soaked tree nuts or prepared nut-based dairy analogs (NBDAs) at home completed the survey. Their responses indicated insufficient knowledge about potential contaminations of tree nuts. Only 25% of participants had heard of a tree nut-related outbreak or recall. Few (30%) participants perceived a risk of contracting a foodborne illness from tree nuts. The participants were more concerned with the health benefits than potential microbial risks of raw tree nuts and preferred government agencies for tree nut food safety information. Based on a cluster analysis, demographics with lower food safety knowledge and risk perceptions (ages 18-24 or 45 and above, female, suburban and rural communities, have less than a bachelor's degree, and earned less than USD 100,000 annually) tended to engage in risky tree nut handling practices (p < 0.05). The findings of this study support the development of audience-targeted food safety extension materials for tree nuts.

Microbiological Assessment of Groundnut (Arachis hypogaea L.) Sold for Consumption in Ghana

The postharvest processes of groundnuts often become sources of microbial contamination leading to infections and intoxication. Hence, this study examined the microbial pathogens contaminating groundnuts after harvesting. About 50 samples were randomly collected from four major groundnut-producing towns: Bolgatanga, Chiana, Navrongo, and Bongo, all in the Upper East Region of Northern Ghana, and microbiologically examined using Analytical Profile Index (API® 20E). The results revealed that samples from Bolgatanga were the most contaminated, while Chiana has the least contaminated samples. Several species of bacterial genera such as Staphylococcus, Proteus, Escherichia, Bacillus, and Micrococcus, and fungal genera including Aspergillus, Fusarium, Rhizopus, Mucor, Saccharomyces, and Eurotium were isolated as the main microbial pathogens contaminating the produce. Navrongo and Bolgatanga recorded the highest rate of bacterial species for unshelled (29.5%) and shelled (30.4%) groundnuts, respectively, while Bongo and Bolgatanga registered the highest rate of fungal species under unshelled (32.8%) and shelled (32.6%) groundnuts, respectively. Due to the high levels of microbial contamination of most of the samples and the kind of microbial species involved, proper hygiene standards must be adopted during the postharvest handling of the shelled and unshelled groundnuts.

Prevalence of Shiga Toxin-Producing Escherichia coli and Salmonella in Native Pecan Orchards as Influenced by Waiting Periods between Grazing and Harvest

ABSTRACT

Animals (grazing, working, or intrusion) in produce production areas may present a potential contamination source of foodborne pathogens on produce. Cattle grazing on native pecan production orchards, a common practice in the southern United States, provides an opportunity to study the impact of grazing practice and waiting periods on contamination rates of foodborne pathogens of tree nuts. Therefore, the objective of this study was to determine the prevalence of Salmonella and Shiga toxin-producing Escherichia coli (STEC) in native pecan production orchards as influenced by waiting periods between grazing cattle and pecan harvest. Soil (10 g), cattle feces (10 g), and in-shell pecans (25 g) were sampled from five cattle-grazed orchards in areas with cattle removed 2 or 4 months before harvest and not removed. Five nongrazing orchards were sampled at harvest for comparison. Detection and isolation of the pathogens were performed by enrichment, selective isolation, and multiplex PCR. Statistical analyses were performed using contingency tables with Pearson's chi-square test. The prevalence of STEC (36%) and Salmonella (29%) in cattle-grazed orchards was significantly higher than in nongrazed orchards (13 and 7%, respectively). STEC prevalence in cattle-grazed orchards was higher (38%) in areas with cattle at harvest than in fenced areas where cattle were removed 2 (29%) and 4 (27%) months before harvest. Salmonella prevalence was similar in areas without fencing (31%) and areas with cattle removed at 2 (22%) and 4 (30%) months before harvest. However, there were no significant differences (P > 0.05) in contamination rates between waiting periods for either pathogen, suggesting a limited impact of waiting periods on reducing the risk of contamination.

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Antibiotic Resistant Enterobacteriaceae in Milk Alternatives

The consumption of non-dairy milk is on the rise due to health benefits. Although there is increasing inclination towards milk alternatives (MA), there is limited data on antibiotic resistant bacteria in these substitutes. The aim of this study was to investigate antimicrobial resistance of bacteria isolated from MA. A total of 138 extracts from almonds (n = 63), cashew nuts (n = 36), and soybeans (n = 39) were analyzed for Enterobacteriaceae. The identification of the bacteria was based on biochemical and PCR methods. Antibiotic sensitivity was determined by using the Kirby-Bauer disk diffusion technique. Overall, 31% (43 of 138) of extracts were positive for Enterobacteriaceae. Ten bacterial species were identified, of which Enterobacter cloacae (42.7%) and Enterobacter cancerogenus (35.4%) were the most predominant species (p < 0.05). Antibiotic resistance was exhibited to vancomycin (88.3%), novobiocin (83.8%), erythromycin (81.1%), which was significantly higher (p < 0.05) than in tetracycline (59.5%), cefpodoxime (30.6%), and nalidixic acid (6.3%). There was no resistance displayed to kanamycin and imipenem. ERY-NOV-VAN-TET and ERY-NOV-CEP-VAN-TET were the most common resistant patterns displayed by Enterobacter cloacae. The findings of this study suggest that MAs, though considered healthy, may be a reservoir of multidrug resistant opportunist pathogens.

Genomic evidence of environmental and resident Salmonella Senftenberg and Montevideo contamination in the pistachio supply-chain

Pistachios have been implicated in two salmonellosis outbreaks and multiple recalls in the U.S. This study performed an in-depth retrospective data analysis of Salmonella associated with pistachios as well as a storage study to evaluate the survivability of Salmonella on inoculated inshell pistachios to further understand the genetics and microbiological dynamics of this commodity-pathogen pair. The retrospective data analysis on isolates associated with pistachios was performed utilizing short-read and long-read sequencing technologies. The sequence data were analyzed using two methods: the FDA's Center for Food Safety and Applied Nutrition Single Nucleotide Polymorphism (SNP) analysis and Whole Genome Multilocus Sequence Typing (wgMLST). The year-long storage study evaluated the survival of five strains of Salmonella on pistachios stored at 25 °C at 35% and 54% relative humidity (RH). Our results demonstrate: i) evidence of persistent Salmonella Senftenberg and Salmonella Montevideo strains in pistachio environments, some of which may be due to clonal resident strains and some of which may be due to preharvest contamination; ii) presence of the Copper Homeostasis and Silver Resistance Island (CHASRI) in Salmonella Senftenberg and Montevideo strains in the pistachio supply chain; and iii) the use of metagenomic analysis is a novel tool for determining the composition of serovar survival in a cocktail inoculated storage study.

Survival of Escherichia coli O157:H7 during Moderate Temperature Dehydration of Plant-Based Foods

The effect of moderate-temperature (≤60 °C) dehydration of plant-based foods on pathogen inactivation is unknown. Here, we model the reduction of E. coli O157:H7 as a function of product-matrix, a_w, and temperature under isothermal conditions. Apple, kale, and tofu were each adjusted to a_w 0.90, 0.95, or 0.99 and inoculated with an E. coli O157:H7 cocktail, followed by isothermal treatment at 49, 54.5, or 60.0 °C. The decimal reduction time, or D-value, is the time required at a given temperature to achieve a 1 log reduction in the target microorganism. Modified Bigelow-type models were developed to determine D-values which varied by product type and a_w level, ranging from 3.0–6.7, 19.3–55.3, and 45.9–257.4 min. The relative impact of a_w was product dependent and appeared to have a non-linear impact on D-values. The root mean squared errors of the isothermal-based models ranged from 0.75 to 1.54 log CFU/g. Second, we performed dynamic drying experiments. While the isothermal results suggested significant microbial inactivation might be achieved, the dehydrator studies showed that the combination of low product temperature and decreasing a_w in the pilot-scale system provided minimal inactivation. Pilot-scale drying at 60 °C only achieved reductions of 3.1 ± 0.8 log in kale and 0.67 ± 0.66 log in apple after 8 h, and 0.69 ± 0.67 log in tofu after 24 h. This illustrates the potential limitations of dehydration at ≤60 °C as a microbial kill step.

Control of Salmonella in low-moisture foods: Enterococcus faecium NRRL B-2354 as a surrogate for thermal and non-thermal validation

Salmonella has been implicated in multiple foodborne outbreaks and recalls associated with low water activity foods (La_wF). To verify the effectiveness of a process against Salmonella in La_wF, validation using a nonpathogenic surrogate strain is essential. Enterococcus faecium NRRL B-2354 strain has been used as a potential surrogate of Salmonella in different processing of La_wF. However, the survival of Salmonella and E. faecium in La_wF during food processing is a dynamic function of a_w, food composition and structure, processing techniques, and other factors. This review assessed pertinent literature on the thermal and non-thermal inactivation of Salmonella and its presumable surrogate E. faecium in various La_wF and provided an overview of its suitibility in different La_wF. Overall, based on the D-values, survival/reduction, temperature/time to obtain 4 or 5-log reductions, most studies concluded that E. faecium is a suitable surrogate of Salmonella during La_wF processing as its magnitude of resistance was slightly greater or equal (i.e., statistical similar) as compared to Salmonella. Studies also showed its unsuitability which either does not provide a proper margin of safety or being overly resistant and may compromise the quality and organoleptic properties of food. This review provides useful information and guidance for future validation studies of La_wF.

Food products as potential carriers of SARS-CoV-2

At present, humanity is confronting with a novel life-threatening challenge from the COVID-19 pandemic infectious disease caused by the novel coronavirus SARS-CoV-2. To date, the various transmission modes of SARS-CoV-2 have not been completely determined. Food products might be carriers for SARS-CoV-2. The COVID-19 pandemic not only can spread through the respiratory tract like SARS and MERS but also the presence of the SARS-CoV-2 RNA in feces of several patients, shows the possibility of their fecal-oral route spread. Besides, people with gastric problems, including gastric intestinal metaplasia and atrophic gastritis, may be susceptible to this kind of COVID-19 infection. Accordingly, food may act as a potential vehicle of SARS-CoV-2 due to whether carry-through or carry-over contaminations. Considering carry-over, SARS-CoV-2 spread from personnel to food products or food surfaces is feasible. Beyond that, some shreds of evidence showed that pigs and rabbits can be infected by SARS-CoV-2. Thus, viral transmission through meat products may be conceivable, indicating carry-through contamination. As the spread rate of SARS-CoV-2 is high and its stability in different environments, especially food processing surfaces, is also remarkable, it may enter foods in whether industrialized processing or the traditional one. Therefore, established precautious acts is suggested to be applied in food processing units. The present review elucidates the risk of various staple food products, including meat and meat products, dairy products, bread, fruits, vegetables, and ready-to-eat foods as potential carriers for transmission of SARS-CoV-2.

The Role of the Salmonella spvB IncF Plasmid and Its Resident Entry Exclusion Gene traS on Plasmid Exclusion

Salmonella enterica cause significant illnesses worldwide. There has been a marked increase in resistance to fluoroquinolones and β-lactams/cephalosporins, antibiotics commonly used to treat salmonellosis. However, S. enterica serovars vary in their resistance to these and other antibiotics. The systemic virulence of some Salmonella serovars is due to a low copy number, IncF plasmid (65–100 kb) that contains the ADP-ribosylating toxin, SpvB. This virulence plasmid is present in only nine Salmonella serovars. It is possible that the spvB-virulence plasmid excludes other plasmids and may explain why antibiotic resistance is slow to develop in certain Salmonella serovars such as S. Enteritidis. The distribution of plasmid entry exclusion genes traS/traT and traY/excA are variable in Salmonella IncF and IncI plasmids, respectively and may account for differences in emergent antimicrobial resistance for some Salmonella serovars. The goal of this study is to determine the contribution of the Salmonella spvB-virulence plasmid in F-plasmid exclusion. From conjugation experiments, S. Typhimurium exhibited lower conjugation frequency with incFI and incFII plasmids when the spvB-virulence plasmid is present. Furthermore, introduction of cloned incFI traS into a “plasmidless” S. Typhimurium LT2 strain and Escherichia coli DH5α excluded incFI plasmid. However, deletion of the virulence plasmid traS did not affect plasmid exclusion significantly compared to a spvB control deletion. In addition, differences in F plasmid conjugation in natural Salmonella isolates did not correlate with IncF or SpvB-virulence plasmid genotype. There appear to be other plasmid or chromosomal genes at play in plasmid exclusion that may be responsible for the slow development of antibiotic resistance in certain serovars.

Effectiveness of Nitrogen Dioxide Fumigation for Microbial Control on Stored Almonds

ABSTRACT

Quality of stored almonds is compromised by insect infestations and microbial contamination. Nitric oxide (NO) is a potent fumigant for postharvest pest control on fresh and stored products. NO fumigation must be conducted under ultralow oxygen conditions, and it always produces nitrogen dioxide (NO2), depending on the O2 level in the fumigation chamber. NO and NO2 have proven antimicrobial effects but have not been tested for efficacy against microbes in almonds. We evaluated, in this study, fumigation of unpasteurized almonds with NO2 at different levels for inhibition of bacteria and fungi. Almonds were fumigated with 0.1, 0.3, or 1.0% NO under ambient O2 to generate 0.1, 0.3, or 1.0% NO2 conditions; the fumigation treatments lasted 1 or 3 days at 25°C. GreenLight rapid enumeration tests on diluted wash-off almond samples from NO2 fumigation treatments showed either greatly reduced microbial loads or complete control of microorganisms, depending on NO2 concentration and treatment duration. NO2 fumigation was more effective against fungi than against bacteria. These results suggest that postharvest NO fumigation with proper levels of NO and NO2 can be used for insect and microorganism control on stored almonds.

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Evaluation of Bead-Based Assays for the Isolation of Foodborne Viruses from Low-Moisture Foods

ABSTRACT

Foodborne viruses such as norovirus and hepatitis A virus (HAV) are highly transmissible, persistent in the environment, and resistant to many conventional inactivation methods. Foods can become contaminated with these viruses either at the source of harvest or during food handling and processing. Multiple lines of evidence suggest that foodborne viruses can survive desiccation and dry conditions. Several foodborne virus outbreaks have been linked to low-moisture foods (LMFs), indicating that these foods can be vehicles of virus transmission. However, the efficiencies of common virus extraction methodologies have not been examined with LMFs. We adapted the International Organization for Standardization (ISO) 15216-1:2017 method for virus recovery for use with chocolate, pistachios, and cornflakes. We also developed a magnetic bead assay for the recovery of HAV from LMFs and used the porcine gastric mucin-coated magnetic beads (PGM-MBs) to extract norovirus surrogates, feline calicivirus (FCV), and murine norovirus (MNV) from the same LMFs. The efficiency of virus recovery using the bead-based assay was then compared with that of the ISO 15216-1:2017 method. In chocolate and pistachios, the recovery rates with the PGM-MB method were 5.6- and 21.3-fold higher, respectively, for FCV and 1.65- and 18-fold higher, respectively, for MNV than those with the ISO 15216-1:2017 method. However, the PGM-MB method failed to recover MNV and FCV from cornflakes. The recovery rates for HAV in chocolate, pistachios, and corn flakes with the magnetic bead method were 11.5-, 3-, and 5.6-fold higher, respectively, than those with the ISO 15216-1:2017 method. Thus, depending upon the food matrix and the target virus, the bead-based assays can be used to efficiently and rapidly extract viruses from LMFs.

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Source Attribution of Salmonella in Macadamia Nuts to Animal and Environmental Reservoirs in Queensland, Australia

Salmonella enterica is a common contaminant of macadamia nut kernels in the subtropical state of Queensland (QLD), Australia. We hypothesized that nonhuman sources in the plantation environment contaminate macadamia nuts. We applied a modified Hald source attribution model to attribute Salmonella serovars and phage types detected on macadamia nuts from 1998 to 2017 to specific animal and environmental sources. Potential sources were represented by Salmonella types isolated from avian, companion animal, biosolids-soil-compost, equine, porcine, poultry, reptile, ruminant, and wildlife samples by the QLD Health reference laboratory. Two attribution models were applied: model 1 merged data across 1998-2017, whereas model 2 pooled data into 5-year time intervals. Model 1 attributed 47% (credible interval, CrI: 33.6-60.8) of all Salmonella detections on macadamia nuts to biosolids-soil-compost. Wildlife and companion animals were found to be the second and third most important contamination sources, respectively. Results from model 2 showed that the importance of the different sources varied between the different time periods; for example, Salmonella contamination from biosolids-soil-compost varied from 4.4% (CrI: 0.2-11.7) in 1998-2002 to 19.3% (CrI: 4.6-39.4) in 2003-2007, and the proportion attributed to poultry varied from 4.8% (CrI: 1-11) in 2008-2012 to 24% (CrI: 11.3-40.7) in 2013-2017. Findings suggest that macadamia nuts were contaminated by direct transmission from animals with access to the plantations (e.g., wildlife and companion animals) or from indirect transmission from animal reservoirs through biosolids-soil-compost. The findings from this study can be used to guide environmental and wildlife sampling and analysis to further investigate routes of Salmonella contamination of macadamia nuts and propose control options to reduce potential risk of human salmonellosis.