**3.4 Use of irrigation waters**

When grown in open fields, leafy greens can become contaminated inside roots and leaves with *E. coli* O157:H7 when irrigation is performed with contaminated water and by the irrigation method [49, 113] and could become the source of many outbreaks [114, 115]. The transmission of the pathogens from contaminated

irrigation waters has been elucidated [50, 116], and secondary vehicles by which *E. coli* O157:H7 may contaminate the leafy greens were identified: flood irrigation with water contaminated either with animal feces or by contact with surface runoff [117, 118]. Experimental and on-field studies indicated the ability of the pathogen to survive for extended periods in water [119, 120].

Many different sources of water and methods are used for irrigation of fresh produce [121]. As water sources are identified two main groups: (a) surface water or treated wastewater (more prone to contamination and presents variables in water quality parameters); and (b) ground water reserves or collected rainfall water (which is less prone to contamination and more controlled from microbial quality standpoint if stored properly). Using drip or subsurface irrigation limits direct contact between edible plant tissue and irrigation water (splashes) and thus is less likely to introduce pathogens than furrow or sprinkler/overhead irrigation. Drip irrigation (subsurface irrigation) has less impact on leafy greens' contact with the pathogen and pathogen survival compared to other irrigation methods such as spraying, surface irrigation, and furrow which favor the subsequent survival of the pathogen up to 56 days [49, 122–124].

On the farm, to ensure the leafy greens protection from pathogen contamination, checking the water source history, application of preventive control measures to prevent contamination or to eliminate the pathogen (i.e., frequent sanitary surveys of water reservoirs and distribution systems, identification, and surveillance of drainages at the confluence points of water sources) are aspects of importance [14, 93, 125]. The preventive control measures are usually combined with different water treatments: filtration, disinfection, or solar irradiation (UV natural treatment) [89, 126, 127]. Similarly, FDA issued a set of GAPs for produce growers which includes: (a) identification of the source and distribution of water used and check its relative potential for being a source of pathogens; (b) maintain water wells in good working condition; (c) revision of existing practices and conditions to identify potential sources of contamination (direct or indirect contamination, contamination from human or animal waste); (d) check the current and historical use of land since agricultural water is frequently a shared resource with other operations or affected by human activity); and (e) test the irrigation water microbial quality [128]. Regarding the GAPs implementation, the Canadian Ministry of Agriculture, Food and Rural Affairs, proposed to farmers additional management practices to avoid or reduce the risk of contamination: (a) choose a different irrigation method (i.e., use drip or trickle irrigation systems rather than overhead sprinklers); (b) choose a different water source, or (c) for some irrigation systems and applications, water treatment is required to improve its quality (**Table 7**) [129].

## **3.5 Other factors which can contribute to pathogen contamination of leafy greens**

#### *3.5.1 Domestic and wild animals*

An extensive number of post-foodborne outbreaks epidemiological surveys recognize the interconnection between animal activity on or in the proximity of growing fields and, leafy greens contamination with pathogenic *E. coli* [49, 130]. Regardless the leafy greens production phase, animals, domesticated (i.e., nearby livestock and on-farm working animals) and wildlife, can shed and transfer *E. coli* O:157:H7 to the produce, even the animals do not display any signs of illness. Among animals themselves, a zoonotic vicious cycle can take place. In many instances, cross contamination via fecal matter between domestic and wild animals have been identified, and approximately 77% of the pathogens

*Pathogenic* Escherichia coli*: An Overview on Pre-Harvest Factors That Impact the Microbial… DOI: http://dx.doi.org/10.5772/intechopen.101552*


#### **Table 7.**

*Best management practices for different irrigation water sources\*.*

that infect livestock can also infect wildlife (deer, geese, rodents, foxes etc.) which, in turn, can re-infect the livestock populations [131, 132]. For the past 10 years, FDA investigation findings on previous foodborne illness outbreak indicate the proximity of cattle operations as a main contributing factor for pathogenic *E. coli* contamination of leafy greens, cattle being repeatedly demonstrated to be a persistent source of E. coli O157:H7 [133]. In addition, leafy greens can become contaminated with antibiotic-resistant *E. coli* which can represent a real danger for public health. This fact was discovered when the *E. coli* isolates from lettuce production sites were compared with the animal-derived *E. coli* strains, and it was determined that these antimicrobial-resistant strains was prevalent in cattle [134]. Due to this high risk, a relatively recent report was issued by the European Food Safety Authority (EFSA) which attempted to ascertain to what extent fresh produce represents a vehicle for the acquisition by humans of antimicrobial-resistant bacteria and to identify possible control options [135–137]. Since food safety is a shared responsibility among all sectors ample animal management guidelines and mitigation strategies were proposed for protecting leafy greens but also fresh produces from being contaminated with pathogens at any stage of production [96, 138]. The on-field protection of the produce against pathogen cross-contamination from the existing multiple sources, regardless if the contamination sources are placed on the farm's premises or outside the farm, several practical protection strategies can used without disturbing the production chain (**Table 8**).


#### **Table 8.**

*Examples of using on-farm management strategies to avoiding leafy greens pathogen contamination\*.*
