On-farm sources of microbial contamination of persimmon fruit in Japan

Evaluation of a novel water-soluble decanoic acid formulation as a fruit sanitizer

Fruits irrigated with contaminated water can transmit various pathogens. High sugar content in fruits such as black cherry (BC) fruit encourages microbial proliferation. A novel water-soluble decanoic acid (WSDA) was evaluated as a fruit sanitizer and compared with other traditional fruit sanitizers such as ethanol, bleach, or dishwasher surfactants. WSDA sanitizer killed yeasts, molds and bacteria including E. coli microbes effectively as other sanitizers with (4 log cycle reduction) of microbial load. Furthermore, the bacterial sanitization mechanism i.e. bactericidal or bacteriostatic was evaluated for alcohol, bleaching and WASDA solutions. E. coli was selected as the model pathogen used for such comparison. Results indicated that the mechanism of action for the three sanitizer solutions against E. coli was bactericidal. The problem with most used fruit sanitizers is their negative influence on fruit quality in terms of physical, mechanical and taste properties. In addition, some led to toxicological and ecological concerns. Thus, studies were conducted to explore the changes in the exocarp cell structure of BC fruit upon exposure to WSDA and other sanitizers using microscopic investigation. WSDA could have a very mild or gentle effect on the BC fruit cells compared to other sanitizers. Alcohol, bleaching and dishwasher surfactant changed the cellular structures and the intercellular spaces. Sanitizers may also affect fruit swelling. WSDA showed an increase in percent weight gain but it was significantly (p < 0.05) much lower than dishwasher surfactant and bleaching solution. BC Fruit flesh firmness and hardness were investigated upon exposure to different sanitizer solutions. BC fruit treated with WSDA showed the highest firmness values. Some liquid sanitizers could affect fruit quality in terms of fruit taste. Sensory evaluation in terms of the sanitizer's smell, texture and hedonic of BC fruit after soaking in different sanitizers was carried out. All sensory parameters of BC fruit soaked with WSDA were similar with insignificant differences (p > 0.05) compared to BC fruit soaked in tap water. However, the sensory parameters were significantly different (p < 0.05) when compared with alcohol, bleach and dishwasher surfactant. This ensures that WSDA was superior to other evaluated sanitizers in terms of physical, mechanical and fruit quality.

Enumeration and Identification of Coliform Bacteria Injured by Chlorine or Fungicide Mixed with Agricultural Water

Chemical sanitizers may induce no injury (bacteria survive), sublethal injury (bacteria are injured), or lethal injury (bacteria die). The proportion of coliform bacteria that were injured sublethally by chlorine and fungicide mixed with agricultural water (pond water), which was used to dilute the pesticide solution, was evaluated using the thin agar layer (TAL) method. In pure cultures of Enterobacter cloacae , Escherichia coli , and E. coli O157:H7 (representing a human pathogen), the percentage of chlorine-injured cells was 69 to 77% for dilute electrolyzed water containing an available chlorine level of 2 ppm. When agricultural water was mixed with electrolyzed water, the percentage of injured coliforms in agricultural water was 75%. The isolation and identification of bacteria on TAL and selective media suggested that the chlorine stress caused injury to Enterobacter kobei . Of the four fungicide products tested, diluted to their recommended concentrations, Topsin-M, Sumilex, and Oxirane caused injury to coliform bacteria in pure cultures and in agricultural water following their mixture with each pesticide, whereas Streptomycin did not induce any injury to the bacteria. The percentage of injury was 45 to 97% for Topsin-M, 80 to 87% for Sumilex, and 50 to 97% for Oxirane. A comparison of the coliforms isolated from the pesticide solutions and then grown on either TAL or selective media indicated the possibility of fungicide-injured Rahnella aquatilis , Yersinia mollaretii , and E. coli . These results suggest the importance of selecting a suitable sanitizer and the necessity of adjusting the sanitizer concentration to a level that will kill the coliforms rather than cause sanitizer-induced cell injury that can result in the recovery of the coliforms.

Spatial and Temporal Factors Associated with an Increased Prevalence of Listeria monocytogenes in Spinach Fields in New York State

While rain and irrigation events have been associated with an increased prevalence of foodborne pathogens in produce production environments, quantitative data are needed to determine the effects of various spatial and temporal factors on the risk of produce contamination following these events. This study was performed to quantify these effects and to determine the impact of rain and irrigation events on the detection frequency and diversity of Listeria species (including L. monocytogenes) and L. monocytogenes in produce fields. Two spinach fields, with high and low predicted risks of L. monocytogenes isolation, were sampled 24, 48, 72, and 144 to 192 h following irrigation and rain events. Predicted risk was a function of the field's proximity to water and roads. Factors were evaluated for their association with Listeria species and L. monocytogenes isolation by using generalized linear mixed models (GLMMs). In total, 1,492 (1,092 soil, 334 leaf, 14 fecal, and 52 water) samples were collected. According to the GLMM, the likelihood of Listeria species and L. monocytogenes isolation from soil samples was highest during the 24 h immediately following an event (odds ratios [ORs] of 7.7 and 25, respectively). Additionally, Listeria species and L. monocytogenes isolates associated with irrigation events showed significantly lower sigB allele type diversity than did isolates associated with precipitation events (P = <0.001), suggesting that irrigation water may be a point source of L. monocytogenes contamination. Small changes in management practices (e.g., not irrigating fields before harvest) may therefore reduce the risk of L. monocytogenes contamination of fresh produce.

Multifactorial effects of ambient temperature, precipitation, farm management, and environmental factors determine the level of generic Escherichia coli contamination on preharvested spinach

A repeated cross-sectional study was conducted to identify farm management, environment, weather, and landscape factors that predict the count of generic Escherichia coli on spinach at the preharvest level. E. coli was enumerated for 955 spinach samples collected on 12 farms in Texas and Colorado between 2010 and 2012. Farm management and environmental characteristics were surveyed using a questionnaire. Weather and landscape data were obtained from National Resources Information databases. A two-part mixed-effect negative binomial hurdle model, consisting of a logistic and zero-truncated negative binomial part with farm and date as random effects, was used to identify factors affecting E. coli counts on spinach. Results indicated that the odds of a contamination event (non-zero versus zero counts) vary by state (odds ratio [OR] = 108.1). Odds of contamination decreased with implementation of hygiene practices (OR = 0.06) and increased with an increasing average precipitation amount (mm) in the past 29 days (OR = 3.5) and the application of manure (OR = 52.2). On contaminated spinach, E. coli counts increased with the average precipitation amount over the past 29 days. The relationship between E. coli count and the average maximum daily temperature over the 9 days prior to sampling followed a quadratic function with the highest bacterial count at around 24°C. These findings indicate that the odds of a contamination event in spinach are determined by farm management, environment, and weather factors. However, once the contamination event has occurred, the count of E. coli on spinach is determined by weather only.

Growth and survival of Enterobacteriaceae and inoculated Salmonella on walnut hulls and maturing walnut fruit

Postharvest contamination of in-shell walnuts may occur when the fruit is dropped to or harvested from the orchard floor or as the outer hull is removed with mechanical abrasion and water. To evaluate the effect of maturity on the potential for microbial contamination, 'Howard' walnut fruits were collected weekly from the tree canopy, from 6 to 7 weeks before to 1 week after typical commercial harvest. The numbers of microorganisms able to form colonies on plate count agar, MacConkey agar (presumptive Enterobacteriaceae), or violet red bile lactose agar (presumptive coliforms) were compared on whole walnut fruits collected by hand directly from the tree or after exposure to the orchard floor for 10 min or 24 h. Salmonella Enteritidis PT 30 was inoculated at <1 to 8 log CFU/g onto 5-g hull pieces (from walnut fruit of different maturities) and stored at ambient temperature (23 to 26°C) in unsealed bags (38 to 90% relative humidity [RH] within bag) or in low humidity (20 to 45% RH) or high humidity (68 to 89% RH) for up to 14 days. Salmonella at 2 or 5 log CFU/ml was inoculated onto hulls before or up to 14 days after blending with water. As the walnut fruit matured, the indigenous bacterial levels on the surface increased, irrespective of whether fruit was collected from the tree or the ground. The RH influenced the growth of inoculated bacteria on hull pieces: Salmonella declined to <0.3 log CFU/g within 24 h at low RH but multiplied from 2 to 6 log CFU/g over 14 days of storage at >40% RH. Salmonella populations declined to <1 CFU/ml within 24 h in freshly blended green hulls but survived or multiplied in blended brown hulls or in blended green hulls that had been stored for 24 h or more before being inoculated.

Risk factors for microbial contamination in fruits and vegetables at the preharvest level: a systematic review

The objective of this study was to perform a systematic review of risk factors for contamination of fruits and vegetables with Listeria monocytogenes, Salmonella, and Escherichia coli O157:H7 at the preharvest level. Relevant studies were identified by searching six electronic databases: MEDLINE, EMBASE, CAB Abstracts, AGRIS, AGRICOLA, and FSTA, using the following thesaurus terms: L. monocytogenes, Salmonella, E. coli O157 AND fruit, vegetable. All search terms were exploded to find all related subheadings. To be eligible, studies had to be prospective controlled trials or observational studies at the preharvest level and had to show clear and sufficient information on the process in which the produce was contaminated. Of the 3,463 citations identified, 68 studies fulfilled the eligibility criteria. Most of these studies were on leafy greens and tomatoes. Six studies assessed produce contamination with respect to animal host-related risk factors, and 20 studies assessed contamination with respect to pathogen characteristics. Sixty-two studies assessed the association between produce contamination and factors related to produce, water, and soil, as well as local ecological conditions of the production location. While evaluations of many risk factors for preharvest-level produce contamination have been reported, the quality assessment of the reviewed studies confirmed the existence of solid evidence for only some of them, including growing produce on clay-type soil, the application of contaminated or non-pH-stabilized manure, and the use of spray irrigation with contaminated water, with a particular risk of contamination on the lower leaf surface. In conclusion, synthesis of the reviewed studies suggests that reducing microbial contamination of irrigation water and soil are the most effective targets for the prevention and control of produce contamination. Furthermore, this review provides an inventory of the evaluated risk factors, including those requiring more research.

Changes in bacterial flora of Japanese cabbage during growth and potential source of flora

Bacterial flora of cabbage were identified and enumerated during various stages of growth, and the potential sources of contamination in the field were determined. Bacterial counts increased from below the level of detection (2.4 log CFU/g) on seeds to 2.5 to 5.7 log CFU/g on seedlings. After transplanting, the counts of mesophilic aerobic bacteria on leaves decreased and then increased to 5.7 log CFU/g on outer leaves, 5.0 log CFU/g on middle leaves, and 3.0 log CFU/g on inner leaves at the harvesting stage. Counts of coliforms were below the level of detection during the growing period of the leaves. Bacteria isolated from cabbage seeds, seedlings, and leaves were soilborne organisms such as Bacillus, Curtobacterium, and Delftia and phytopathogenic organisms such as Pseudomonas, Pantoea, and Stenotrophomonas. These bacteria were found frequently in seeding machines, potting soil mix, soil, agricultural water, pesticide solutions mixed with the agricultural water, liquid fertilizers, and chemical fertilizers. Contamination from these environmental sites occurred throughout the cabbage growing period rather than only at the harvesting stage. These results indicate that use of clean water for irrigation and for mixing with pesticides and amendments from seeding to the harvesting stage is an important part of a good agricultural practices program for cabbage in Japan.

Transfer of Salmonella enterica serovar Typhimurium from contaminated irrigation water to parsley is dependent on curli and cellulose, the biofilm matrix components

Enteric pathogens can contaminate fresh produce, and this contaminated produce can be a significant potential source of human illness. The objective of this study was to determine a possible mode of transfer of Salmonella Typhimurium from contaminated irrigation water to mature parsley plants and to investigate the role of bacterial cellulose and curli. Parsley plants were drip irrigated with water containing green fluorescent protein-labeled Salmonella Typhimurium. Stems and leaves were harvested 1 day after the third irrigation and examined for the presence of Salmonella Typhimurium. Three weeks after harvesting, the presence of Salmonella was again confirmed in the regrown plants. During this period, bacterial numbers on leaves declined from 4.1 (+/- 0.3) to 2.3 (+/- 0.1) log CFU g(-1) (P < 0.05). Numbers in the soil were constant (5 log CFU g(-1)). Results demonstrated the ability of Salmonella Typhimurium to transfer from irrigation water to the edible parts of the plants. Confocal laser scanning microscopic images revealed that Salmonella Typhimurium formed aggregates at a depth of 8 to 32 microm beneath the leaf surface. Penetration might be achieved through the roots or the phyllosphere. The importance of the bacterial cellulose and curli was determined by comparing the wild-type strain with its mutants, which lack the ability to synthesize cellulose and curli. Counts of the double mutant were 2-log higher in the soil but 1-log lower in the leaves (P < 0.05). Deletion of the agfBA gene (for curli) was more effective than deletion of bcsA (for cellulose). Thus, curli and cellulose play a role in the transfer or survival of Salmonella Typhimurium in the plant, as they do for plant pathogens.

Precut prepackaged lettuce: a risk for listeriosis?

The most recent outbreaks of listeriosis have been traced back to contaminated ready-to-eat (RTE) poultry and meat products. However, Listeria monocytogenes can be isolated from every food group, including fresh vegetables. This review is focused on one of the most popular RTE vegetable products, precut prepackaged lettuce. The available literature concerning Listeria contamination of vegetables is reviewed, and possible reasons why no recent outbreaks or sporadic cases of listeriosis due to contaminated precut prepackaged lettuce are explored.

Sanitation and Microbiological Quality in Production Field and Fruit-Packing Shed of Persimmon and Satsuma Mandarin in Japan

The effects of sanitation treatments including chlorination (ca 10 ppm available chlorine) of agricultural water and ethyl alcohol (70%) spraying on packing shed equipment on microbial contamination on fruits and the environment were determined and compared with those in conventionally managed field and packing shed in persimmon and satsuma mandarin orchards. Chlorinated water reduced the microbial counts to levels below the lower limit of detection (1.4 log CFU/ml for bacteria and 2.0 log CFU/ml for fungi) in most agricultural water samples. Microbial counts of pesticide solution, which contained the agricultural water or chlorinated water for the mixture, were lower in sanitary field than in control field in both fruit orchards. The number of bacterial and mold species detected in agricultural water, chlorinated water, and pesticide solution were almost proportional to microbial counts in each sample throughout the year. The chlorination treatment of agricultural water tended to reduce the counts of mesophiles and fungi on the peel of persimmon fruit during production season. The ethyl alcohol spray treatment on packing shed equipment resulted in a substantial microbial reduction on plastic harvest basket and container in persimmon orchard and plastic harvest basket and container, gloves, scissors, and size sorter in satsuma mandarin orchard. The spray application on packing shed equipment reduced the counts of mesophiles and fungi on the peel of persimmon fruit by >1 log CFU/g. The number of satsuma mandarin packing shed equipment containing the species found on fruit peel was higher in control than in sanitary packing shed. No human pathogens such as verotoxin-producing Escherichia coli and Salmonella were detected in any of the fruit and environmental samples. These results indicate that uses of sanitizers such as chlorine for agricultural water and ethyl alcohol for packing shed equipment would be useful in a good agricultural practices program of persimmons and satsuma mandarin.