ARS | Publication request: Characterization of Salmonella spp. from nopal leaves and associated soil and water samples in Morelos, Mexico

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 14, 2009
Publication Date: July 20, 2009
Citation: Hernandez, A.M., Landa, P., Mora-A, G., Eslava, A., Call, J.E., Porto Fett, A.C., Luchansky, J.B. 2009. Characterization of Salmonella spp. from nopal leaves and associated soil and water samples in Morelos, Mexico. [abstract]. International Association for Food Protection. p.1.

Technical Abstract: Introduction: Nopal is a native cactus specie [Opuntia ficus-indica (L.) MILL (Cactaceae)] of great economic importance in Mexico. It is grown in open fields and subsequently ingested fresh as a salad or processed as a juice or yogurt, but it may also be used as a dietary supplement and/or for cosmetic products. Recent Salmonella outbreaks have resulted in renewed concerns about the incidence and control of this bacterium particularly in fresh fruits and vegetables such as cantaloupe, tomatoes, bell peppers, and jalapeños. Purpose: The objective of this study was to determine the bacteriological safety of fresh cactus leaves (nopal) and the associated soil and water in Morelos, a cactus-producing region of south central Mexico. Methods: A total of 34 samples (18 cactus leaves, 8 soil, and 8 water) were taken randomly from the high, middle, and low levels of a nopal production field between May and June of 2006. Traditional microbiological methods (NOM-114-SSA1-1994) and the PCR were used to determine the prevalence of the pathogen and serotyping, ribotyping, and PFGE were used to further confirm and characterize the isolates. Results: Based on both microbiological and PCR analyses, 23 of 34 total samples (67.4% prevalence; 12 positive samples from nopal leaves, 7 from surrounding soil, and 4 from pond/irrigation water) were positive for Salmonella spp. Serotyping revealed that the isolates were either S. Typhimirium or S. javiana. The results from PFGE of selected isolates (10 from cactus leaves, 3 from soil, and 2 from water) revealed that the isolates displayed 3 pulsotypes. Most isolates (8 of 16 isolates; 2 from water and 6 from nopal leaves) belonged to pulsotype III, whereas pulsotype I contained 6 isolates (4 from nopal leaves and 2 from soil) and pulsotype II contained 2 isolates (both from soil). It was possible to associate strains from nopal leaves with those recovered from water or soil based on pulsotype, but it was not possible to associate isolates from soil with those from water based on PFGE. Significance: These data suggest that nopal may become contaminated with Salmonella from both water and soil and suggests that it may serve as a vehicle for transmission of this pathogen to the public, particularly those at higher risk, who may consume fresh or processed nopal.