Comparative assessment of field survival of Salmonella enterica and E. coli O157:H7 on cilantro (Coriandrum sativum) in relation to sequential cutting and re-growth.

The proposed research seeks to significantly narrow the knowledge gaps in food safety management of a very popular and widely used culinary herb, cilantro. The problem facing growers, foodservice and retail marketers, and public health officials is primarily the high detection prevalence of Salmonella on cilantro in produce surveys. Multistate outbreaks and multiple costly recalls have elevated these concerns over the past five years, in particular. Field-based research with non-pathogenic forms of Salmonella and E. coli O157:H7 will be conducted in California to determine the survival, growth potential, and postharvest removal efficiencies following simulated foliar contact contamination events during production. While the interactions between Salmonella and cilantro in laboratory studies have clearly shown that pathogen growth is likely at non-refrigerated temperatures, especially following dicing for foods such as salsas, our understanding of risk potential in more ‘real-world’ production conditions is largely absent. We anticipate that the outcomes of our research will foster the development and adoption of Best Practices in food safety management among cilantro growers and processors. This knowledge will be largely transferrable to other leafy culinary herbs including parsley and basil.

Since 2004, cilantro has garnered an increasing negative reputation for its association with contamination by Salmonella and shiga-toxin producing E.coli . Risk characterization studies to determine the fitness of attenuated isolates of Escherichia coli O157:H7 and Salmonella enterica to survive and establish on cilantro leaves will be performed in open field environments. In this project, designed in response to industry request, we aim to determine quantitatively and qualitatively the acute survival, persistence, and potential for dispersal after foliar applied contamination of these bacteria to cilantro. Inoculum levels will be from log 4 to log 6 CFU/mL. Quantitative analysis will be conducted using standard selective and differential enumeration media with and without membrane filtration as well as semi-quantitative qrtPCR methods for direct estimation of target pathogen presence on cilantro. If direct detection is negative, qualitative detection will be comparatively conducted by various commercial kit formats and research style probe-based qrtPCR. This risk characterization will encompass the standard sequential harvest and re-growth intervals typical of preharvest operations with cilantro. Field research timing will include moderate to warm seasonal climate as well as hot-dry environments to compare the fate of both pathogen surrogates under different environmental conditions. Following establishment on plants under environmental stresses, we will mimic harvest and postharvest operations including, cooling, washing, packing and distribution to point of purchase or point of consumption using optimal as well as sub-optimal conditions to determine the growth potential of E. coli O157:H7 and S. enterica. Postharvest wash and cooling studies will determine the minimal water treatment process parameters to prevent cross-contamination and quantify the log-reduction from cilantro surfaces that may be anticipated in field adapted contamination. We anticipate that the outcomes of this research will be of immediate interest and use by cilantro suppliers, as well as producers of other culinary herbs, by elucidating a science based approach to supply-chain management of food safety challenges.

1. To determine the quantitative and qualitative survival of Salmonella enterica and Escherichia coli O157:H7 on cilantro leaves after foliar applied contamination during pre-harvest production. 

2. To determine the degree of persistence and dispersal of Salmonella enterica and Escherichia coli O157:H7 in sequential harvest and re-growth intervals. 

3. Determine the impact of delays to cooling, specific temperature thresholds, and postharvest washing on growth potential and cross contamination of applied pathogen-surrogates, including simulated industrial pilot-plant processing and simulated retail distribution.

Culinary herbs could be at risk of persistent contamination with human bacterial pathogens that may follow from preharvest events to postharvest handling and distribution. Though not a novel observation, it is clear that once contamination occurs, establishment and firm attachment of the pathogens to the surface of cilantro is likely to occur and be persistent for at least 12 days, depending on many physical and biological factors (Poza-Carrion et al., 2013). Furthermore, persistent under field conditions is likely to be dependent on a combination of dose and physiological adaptation to acute stress, associated with the nature of the associated matrix (water vs. fecal matter) following deposition. The persistence of enteric bacteria can extend beyond the phases of non-lethal postharvest processing including commercial washing with disinfectants and typical supply-chain conditions of commercial storage, particularly if temperature abuse occurs. The efficiency of different commercial washing and disinfection strategies is also dependent on the level of contamination and detachment of the pathogen, however there is always a risk of cross-contamination through the water or through the plant material contact-points