Absence of direct association between coliforms and Escherichia coli in irrigation water and on produce

New strategies for the enumeration of enteric pathogens in water

Water quality standards for drinking water and recreational waters have long been based on the enumeration of faecal coliforms in the various water supplies, with 0 CFU Escherichia coli/100 ml for drinking water and <126 CFU generic E. coli/100 ml for recreational waters. Irrigation water will soon undergo the same scrutiny in the United States. For over 50 years the most probable number method has been used by laboratories to estimate the level of viable bacteria in a sample, but this method is labour intensive and slow, especially if large numbers of samples need to be tested. In this review, we describe some recent innovations in methods to enumerate enteric pathogens in water. These methods are based on different reasoning schemes that can be categorized as biosensors and nucleic acid-based methods. All the methods described here used natural water sources. Several were also used to survey the bacterial levels in naturally contaminated samples. The different methods vary in their limits of detection, ease of use, and potential portability. Some combine very good limits of detection with the ability to overcome technical challenges; however, there is considerable room for improvement, as none of the methods are without shortcomings.

Regulatory Issues Associated with Preharvest Food Safety: United States Perspective

The preharvest and preslaughter steps of food production constitute a first stage at which food can become contaminated with foodborne and toxigenic pathogens. Contamination at this early stage of food production can lead to amplification as food travels through the production and supply chain, accentuating the crucial need to address hazards and establish science-based metrics that are feasible to implement. This article discusses the preharvest food safety regulatory landscape in the United States, with a specific emphasis on fresh produce crops. Best practices, certification, audit schemes and challenges due to market channels, economies of scales, and grower behavior are considered in relation to the Food Safety Modernization Act. An outlook on the needs to facilitate implementation of the new law, develop educational programs for growers and stakeholders, and continue to better align food safety with environmental goals are presented.

Contamination of Fresh Produce by Microbial Indicators on Farms and in Packing Facilities: Elucidation of Environmental Routes

To improve food safety on farms, it is critical to quantify the impact of environmental microbial contamination sources on fresh produce. However, studies are hampered by difficulties achieving study designs with powered sample sizes to elucidate relationships between environmental and produce contamination. Our goal was to quantify, in the agricultural production environment, the relationship between microbial contamination on hands, soil, and water and contamination on fresh produce. In 11 farms and packing facilities in northern Mexico, we applied a matched study design: composite samples (n = 636, equivalent to 11,046 units) of produce rinses were matched to water, soil, and worker hand rinses during two growing seasons. Microbial indicators (coliforms, Escherichia coli, Enterococcus spp., and somatic coliphage) were quantified from composite samples. Statistical measures of association and correlations were calculated through Spearman's correlation, linear regression, and logistic regression models. The concentrations of all microbial indicators were positively correlated between produce and hands (ρ range, 0.41 to 0.75; P < 0.01). When E. coli was present on hands, the handled produce was nine times more likely to contain E. coli (P < 0.05). Similarly, when coliphage was present on hands, the handled produce was eight times more likely to contain coliphage (P < 0.05). There were relatively low concentrations of indicators in soil and water samples, and a few sporadic significant associations were observed between contamination of soil and water and contamination of produce. This methodology provides a foundation for future field studies, and results highlight the need for interventions surrounding farmworker hygiene and sanitation to reduce microbial contamination of farmworkers' hands.IMPORTANCE This study of the relationships between microbes on produce and in the farm environment can be used to support the design of targeted interventions to prevent or reduce microbial contamination of fresh produce with associated reductions in foodborne illness.

Microbial Quality, Safety, and Pathogen Detection by Using Quantitative PCR of Raw Salad Vegetables Sold in Dhanbad City, India

Consumption of ready-to-eat fresh vegetables has increased worldwide, with a consequent increase in outbreaks caused by foodborne pathogens. In the Indian subcontinent, raw fresh vegetables are usually consumed without washing or other decontamination procedures, thereby leading to new food safety threats. In this study, the microbiological quality and pathogenic profile of raw salad vegetables was evaluated through standard protocols. In total, 480 samples (60 each of eight different salad vegetables) of cucumber, tomato, carrot, coriander, cabbage, beetroot, radish, and spinach were collected from different locations in Dhanbad, a city famous for its coal fields and often called the "Coal Capital of India." The samples were analyzed for total plate count, total coliforms, Escherichia coli , E. coli O157:H7, Listeria monocytogenes , and Salmonella spp. Incidences of pathogens were detected through quantitative PCR subsequent to isolation. Results showed that 46.7% (for total plate counts) and 30% (for total coliforms) of samples were unacceptable for consumption per the Food Safety and Standards Authority of India. Pathogenic microorganisms were detected in 3.7% of total samples. E. coli O157:H7 was detected in three samples of spinach (2) and beetroot ( 1 ); L. monocytogenes was detected in 14 samples of spinach ( 8 ), tomato ( 3 ), cucumber ( 2 ), and radish ( 1 ); and Salmonella spp. were detected in 16 samples of spinach ( 7 ), tomato ( 3 ), beetroot ( 2 ), cucumber ( 2 ), carrot ( 1 ), and radish ( 1 ). Pathogens were not detected in any of the cabbage and coriander samples.

Assessment of Primary Production of Horticultural Safety Management Systems of Mushroom Farms in South Africa

Growing global consumer concern over food safety in the fresh produce industry requires producers to implement necessary quality assurance systems. Varying effectiveness has been noted in how countries and food companies interpret and implement food safety standards. A diagnostic instrument (DI) for global fresh produce industries was developed to measure the compliancy of companies with implemented food safety standards. The DI is made up of indicators and descriptive grids for context factors and control and assurance activities to measure food safety output. The instrument can be used in primary production to assess food safety performance. This study applied the DI to measure food safety standard compliancy of mushroom farming in South Africa. Ten farms representing almost half of the industry farms and more than 80% of production were independently assessed for their horticultural safety management system (HSMS) compliance via in-depth interviews with each farm's quality assurance personnel. The data were processed using Microsoft Office Excel 2010 and are represented in frequency tables. The diagnosis revealed that the mushroom farming industry had an average food safety output. The farms were implementing an average-toadvanced HSMS and operating in a medium-risk context. Insufficient performance areas in HSMSs included inadequate hazard analysis and analysis of control points, low specificity of pesticide assessment, and inadequate control of suppliers and incoming materials. Recommendations to the industry and current shortcomings are suggested for realization of an improved industry-wide food safety assurance system.

Microbial Survey of Pennsylvania Surface Water Used for Irrigating Produce Crops

Recent produce-associated foodborne illness outbreaks have been attributed to contaminated irrigation water. This study examined microbial levels in Pennsylvania surface waters used for irrigation, relationships between microbial indicator organisms and water physicochemical characteristics, and the potential use of indicators for predicting the presence of human pathogens. A total of 153 samples taken from surface water sources used for irrigation in southeastern Pennsylvania were collected from 39 farms over a 2-year period. Samples were analyzed for six microbial indicator organisms (aerobic plate count, Enterobacteriaceae, coliform, fecal coliforms, Escherichia coli, and enterococci), two human pathogens (Salmonella and E. coli O157), and seven physical and environmental characteristics (pH, conductivity, turbidity, air and water temperature, and sampling day and 3-day-accumulated precipitation levels). Indicator populations were highly variable and not predicted by water and environmental characteristics. Only five samples were confirmed positive for Salmonella, and no E. coli O157 was detected in any samples. Predictive relationships between microbial indicators and the occurrence of pathogens could therefore not be determined.

Irrigation Water Quality for Leafy Crops: A Perspective of Risks and Potential Solutions

There is increasing evidence of the contribution of irrigation water in the contamination of produce leading to subsequent outbreaks of foodborne illness. This is a particular risk in the production of leafy vegetables that will be eaten raw without cooking. Retailers selling leafy vegetables are increasingly targeting zero-risk production systems and the associated requirements for irrigation water quality have become more stringent in regulations and quality assurance schemes (QAS) followed by growers. Growers can identify water sources that are contaminated with potential pathogens through a monitoring regime and only use water free of pathogens, but the low prevalence of pathogens makes the use of faecal indicators, particularly E. coli, a more practical approach. Where growers have to utilise water sources of moderate quality, they can reduce the risk of contamination of the edible portion of the crop (i.e., the leaves) by treating irrigation water before use through physical or chemical disinfection systems, or avoid contact between the leaves and irrigation water through the use of drip or furrow irrigation, or the use of hydroponic growing systems. This study gives an overview of the main problems in the production of leafy vegetables associated with irrigation water, including microbial risk and difficulties in water monitoring, compliance with evolving regulations and quality standards, and summarises the current alternatives available for growers to reduce microbial risks.

Comparing the microbiological status of pre- and postharvest produce from small organic production

Consumption of locally, organically grown produce is increasing in popularity. Organic farms typically produce on a small scale, have limited resources, and adopt low technology harvest and postharvest handling practices. Data on the food safety risk associated with hand harvesting, field packing, and packing-house handling with minimal treatment, at this production scale, are lacking. We followed produce from small organic farms from the field through postharvest handling and packing. Pre- and postharvest produce (177 samples) and water (29 samples) were collected and analyzed quantitatively for Escherichia coli, total coliforms (TC), aerobic bacteria (APC), yeasts, molds (M), and enteric pathogens. No pathogens were recovered. E. coli was detected in 3 (3.6%) of 83 preharvest produce samples, 2 (6.3%) of 32 unwashed and 0 of 42 washed postharvest produce samples, and 10 (34.5%) of 29 water samples. No correlation was found between bacterial levels in irrigation water and those on produce. Postharvest handling without washing was a factor for APC and M counts on tomatoes, with lower frequencies postharvest. Postharvest handling with washing was a factor for leafy greens for TC counts, with higher frequencies postharvest. APC (P = 0.03) and yeast (P = 0.05) counts were higher in preharvest than in unwashed postharvest tomatoes. Washed postharvest leafy greens had higher M counts (P = 0.03) and other washed produce had higher TC counts (P = 0.01) than did their preharvest counterparts. Barriers were found to the use of sanitizer in wash water for leafy greens among small farms using organic practices. Hand harvesting and dry handling did not appear to be associated with a significant food safety risk, but washed leafy greens carried higher levels of some microbial indicators, possibly because of the lack of sanitizer in the wash water. The development of resources and materials customized for this sector of growers could enhance dissemination of information on best practices for handling of leafy greens.

Associations between weather and microbial load on fresh produce prior to harvest

Contaminated produce causes approximately 1 million cases of foodborne illness and 1 billion dollars in damages to the U.S. economy annually. The environmental conditions, especially weather, that influence the inoculation, proliferation, and dispersal of microbial load on produce are not well understood. Using a mixed models approach, we examined the relationship of temperature and precipitation to microbial indicators of contamination on fresh produce on the farm over a week-long period prior to harvest. Between 2000 and 2002, we assayed for four microbial indicators of contamination (aerobic plate count, Enterococcus, total coliforms, and Escherichia coli) on 10 produce types in 15 fields in the southern United States. The sample collection times varied, with most occurring between January and May. We collected hourly weather data for the corresponding time period and location. Our results indicated that there was a significant association between the average daily temperature (20°C) and both log aerobic plate count (e.g., an increase of 0.074 log CFU/g [standard error {SE}, 0.023] per °C increase in weekly average temperature) and log Enterococcus (e.g., an increase of 0.15 log CFU/g [SE, 0.031] per °C increase in weekly average temperature) for approximately 5 days prior to sample collection. Daily total precipitation was significantly associated with log coliforms on 2 days (∼0.11 log CFU/g [SE, 0.06] per mm of precipitation) during the week-long lag period prior to harvest. Our results suggest that microbial indicator concentrations may increase as the temperature increases. Precipitation may have a positive but complex relationship with microbial indicators, as precipitation may create moist conditions conducive to bacterial growth, spread contamination onto the field, or wash contamination off of the plant.

Contamination of tomatoes with coliforms and Escherichia coli on farms and in markets of northwest Nigeria

Although recent reports indicated that produce contamination with foodborne pathogens is widespread in Nigeria, the sources and magnitude of microbial contamination of fruits and vegetables on farms and in markets have not been thoroughly identified. To ascertain possible pathways of contamination, the frequency and magnitude of coliform and Escherichia coli contamination of tomatoes produced in northwest Nigeria was assessed on farms and in markets. Eight hundred twenty-six tomato fruit samples and 36 irrigation water samples were collected and assessed for fecal indicator organisms. In addition, the awareness and use of food safety practices by tomato farmers and marketers were determined. Median concentration of coliforms on all field- and market-sourced tomato fruit samples, as well as in irrigation water sources, in Kaduna, Kano, and Katsina states exceeded 1,000 most probable number (MPN) per g. Median E. coli counts from 73 (17%) of 420 field samples and 231 (57%) of 406 market tomato fruit samples exceeded 100 MPN/g. Median E. coli concentrations on tomato fruits were higher (P < 0.01) in the rainy season (2.45 Log MPN/g), when irrigation was not practiced than in the dry (1.10 Log MPN/g) and early dry (0.92 Log MPN/g) seasons. Eighteen (50%) of 36 irrigation water samples had E. coli counts higher than 126 MPN/100 ml. Median E. coli contamination on market tomato fruit samples (2.66 Log MPN/g) were higher (P < 0.001) than those from tomatoes collected on farms (0.92 Log MPN/g). Farmers and marketers were generally unaware of the relationship between food safety practices and microbial contamination on fresh produce. Good agricultural practices pertaining to food safety on farms and in local markets were seldom used. Adoption of food safety practices on-farm, during transport, and during marketing could improve the microbial quality of tomatoes available to the public in this region of the world.

Can E. coli or thermotolerant coliform concentrations predict pathogen presence or prevalence in irrigation waters?

An increase in food-borne illnesses in the United States has been associated with fresh produce consumption. Irrigation water presents recognized risks for microbial contamination of produce. Water quality criteria rely on indicator bacteria. The objective of this review was to collate and summarize experimental data on the relationships between pathogens and thermotolerant coliform (THT) and/or generic E. coli, specifically focusing on surface fresh waters used in or potentially suitable for irrigation agriculture. We analyzed peer-reviewed publications in which concentrations of E. coli or THT coliforms in surface fresh waters were measured along with concentrations of one or more of waterborne and food-borne pathogenic organisms. The proposed relationships were significant in 35% of all instances and not significant in 65% of instances. Coliform indicators alone cannot provide conclusive, non-site-specific and non-pathogen-specific information about the presence and/or concentrations of most important pathogens in surface waters suitable for irrigation. Standards of microbial water quality for irrigation can rely not only on concentrations of indicators and/or pathogens, but must include references to crop management. Critical information on microbial composition of actual irrigation waters to support criteria of microbiological quality of irrigation waters appears to be lacking and needs to be collected.