Molecular sequence typing reveals genotypic diversity among Escherichia coli isolates recovered from a cantaloupe packinghouse in Northwestern Mexico

Authors: Quinones, Beatriz; CAMPOS-SAUCEDA, JUAN - Instituto Tecnológico De Culiacan; Lee, Bertram; Yambao, Jaszemyn; CHAIDEZ, CRISTOBAL - Center For Research In Food And Development (CIAD)

Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2017
Publication Date: 4/28/2017
Citation: Quinones, B., Campos-Sauceda, J.P., Lee, B.G., Yambao, J.C., Chaidez, C. 2017. Molecular sequence typing reveals genotypic diversity among Escherichia coli isolates recovered from a cantaloupe packinghouse in Northwestern Mexico. Letters in Applied Microbiology. doi: 10.1111/lam.12733.

Interpretive Summary: Over the past decades, the increased consumption of fresh fruit and vegetables in the United States has contributed to a demand for year round availability. This supply for fresh produce has been enabled by technologies to extend the produce shelf-life as well as by import trade agreements to provide products that are out of season in the United States. In particular, fresh fruit and vegetables grown in Mexico have been the main source of this increased trend for produce imports, and Mexico has thus become the largest supplier to the United States. The trend of increased consumption of fruit and vegetables has been followed by an increase in the number of reported outbreaks attributed to bacterial pathogens. These findings have highlighted the need for identifying source attributions to help design better strategies for prevention and intervention control measures. Among the predominant varieties of melons, cantaloupes have been frequently implicated in produce associated outbreaks. Cantaloupes grown in the United States and those imported from multiple geographical locations in Mexico and Central America have been implicated in twelve multistate outbreaks from 1989 to 2012; an average of one outbreak every two years in the United States. When compared to other melon varieties, cantaloupes have a rough and netted surface with pits and crevices, which may enable the adherent bacteria to resist removal by washing treatments. These surface properties of the cantaloupes are thought to be one of many potential reasons for these outbreaks associated with cantaloupe consumption. Packinghouses are considered as a potential source of microbial contamination. As a result of post-harvest processing, fresh produce in a packinghouse come into contact with multiple surfaces and sources. Moreover, inefficient sanitation of handlers and processing equipment as well as improper disinfection of wash water can contribute to harbor microorganisms and contaminate the fresh produce. Previous reports identified risk factors associated with sources of contamination in cantaloupe packinghouses, located in southern states in the United States and eastern and western states in Mexico However, studies on potential sources of contamination in cantaloupe packinghouses from other agricultural states in Northwestern Mexico are lacking. One of these agricultural states is Sonora, which is a major agricultural state, known for having an active cantaloupe industry for exportation. In particular, no research evidence is available on the genotypic classification of recovered Escherichia coli isolates from different sources and operational stages in a cantaloupe packinghouse in Sonora. To identify potential risk factors associated with post-harvest handling and processing practices, the present study employed a sequence-based method, multilocus sequence typing (MLST), for the genotypic characterization of E. coli isolates, recovered from various sources and operational stages at a cantaloupe packinghouse. The results obtained from this genomic indexing study revealed that the surfaces of cantaloupes, workers’ hands and processing equipment from distinct operational stages in the packinghouse are all potential routes of a genotypic and phylogenetically diverse set of E. coli isolates. These findings have set a precedent for the evaluation of potential sources of contamination and could aid in the development of preventive measures to reduce bacterial contamination of cantaloupes in packinghouses in Northwestern Mexico.

Technical Abstract: The increase in the consumption of fresh produce in the United States has correlated with a rise in the number of reported foodborne illnesses. To identify potential risk factors associated with post-harvest practices, the present study employed multilocus sequence typing (MLST) for the genotypic classification of Escherichia coli isolates, recovered from various sources and operational stages at a cantaloupe packinghouse in Northwestern Mexico. The MLST analysis results indicated that the E. coli isolates were classified into 18 different sequence types (ST), and 11 of these STs were found to be novel. ST-171 was the predominant type and was found in 19% (7/36) of the recovered isolates. Interestingly, the novel ST-827 was found to be significantly associated with isolates recovered from workers’ hands, sampled during final post-wash stages. Further phylogenetic analyses to examine the relatedness of the STs revealed genetic heterogeneity. Fourteen of the identified STs were assigned to known clonal groups while the remaining four novel STs were distinct and did not cluster with any clonal group. The present study has provided the first evidence indicating that several sources from distinct operational stages in a cantaloupe packinghouse may contribute to a genotypic and phylogenetic diverse set of E. coli isolates.