Association of Escherichia coli O157:H7 with Preharvest Leaf Lettuce upon Exposure to Contaminated Irrigation Water

Abstract

Recent foodborne outbreaks have linked infection by enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 to the consumption of contaminated lettuce. Contamination via food handler error and on-the-farm contamination are thought to be responsible for several outbreaks. Though recent studies have examined the application of EHEC to store-bought lettuce, little is known about the attachment of EHEC to growing plants. We investigated the association of lettuce seedlings with EHEC O157:H7 strains implicated in lettuce or fruit outbreaks using hydroponic and soil model systems. EHEC strains that express the green fluorescent protein were observed by stereomicroscopy and confocal laser scanning microscopy to determine adherence patterns on growing lettuce seedlings. Bacteria adhered preferentially to plant roots in both model systems and to seed coats in the hydroponic system. Two of five nonpathogenic E. coli strains showed decreased adherence to seedling roots in the hydroponic system. EHEC was associated with plants in as few as 3 days in soil, and contamination levels were dose-dependent. EHEC levels associated with young plants inoculated with a low dose suggested that the bacteria had multiplied. These data suggest that preharvest crop contamination via contaminated irrigation water can occur through plant roots.

Wastewater reuse in irrigation: A microbiological perspective on implications in soil fertility and human and environmental health

“…The occurrence of pathogens in treated domestic wastewater is well documented (Okoh et al, 2007;Varela and Manaia, 2013) and their transmission to humans by direct contact or through the food chain is of concern (Hussain et al, 2002;Solomon et al, 2002;Steele and Odumeru, 2004;Wachtel et al, 2002). In addition, indirect transmission pathways include the air, due to the formation of aerosols, or water, due to runoff or leaching (Hussain et al, 2002).…”

“…Species comprising opportunistic pathogens such as Escherichia coli, Enterobacter cloacae and Klebsiella pneumoniae were detected in vegetables after irrigation with wastewater (Al-Lahham et al, 2003;Ibenyassine et al, 2007). A good example is the enterohemorrhagic strain E. coli O157:H7 that can be internalized into lettuce when exposed to contaminated irrigation water or soil (Solomon et al, 2002;Wachtel et al, 2002). Moreover, because plants are privileged hosts for these bacteria, if supplied in irrigation water, they can proliferate and survive for longer periods when plants are present than in their absence (Gagliardi and Karns, 2002;Ibekwe et al, 2004;Tyler and Triplett, 2008).…”

Concomitant uptake of antimicrobials and Salmonella in soil and into lettuce following wastewater irrigation

“…Salmonella enterica serovars Cubana and Dublin accumulate inside hydroponically grown alfalfa and lettuce at the level of 4 log CFU/g fresh weight through root uptake (Dong et al, 2003;Klerks et al, 2007b). Internalization of human pathogens can also occur through root uptake when the pathogens are introduced by contaminated soil or irrigation water ( Franz et al, 2007, Hintz et al, 2010, Hora et al, 2005, Klerks et al, 2007aand Wachtel et al, 2002. Few prior studies have investigated wastewater irrigation as a continuous exposure route for the co-uptake of antimicrobials and pathogens into food crops.…”

Determination of Microbial Growth and Survival in Salad Vegetables through in Vitro Challenge Test

“…The practice of consuming fresh vegetables remains popular around the world due to their nutritional value and the ease of availability [31,34,35]. However, fresh vegetables may come in contact with an array of microorganisms resulting in various diseases [5,7,17,22,27,30,33].…”