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Response of Vegetable Cactus Pads to Salmonella Strains

De la Riva-Álvarez, S. L. (Colegio de Postgraduados–Montecillo, México) Hernández-Anguiano A. M.* (Colegio de Postgraduados–Montecillo, México) Corrales -García J.E. (Universidad Autónoma Chapingo-México) Soto-Hernández M. (Colegio de Postgraduados–Montecillo, México) Patel J. (USDA-Beltsville, Maryland, USA) Reyes Trejo B.(Universidad Autónoma Chapingo-México) Zavaleta-Mancera H. A. (Colegio de Postgraduados-Montecillo, México)

Tender cactus pads or nopalitos (Opuntia ficus-indica L) are an important vegetable in México. They are often pre-trimmed, cut and packaged, and while usually consumed cooked, they may also be eaten raw in salads. Salmonella is an enteropathogenic bacterium that can adapt to adverse environmental conditions. Although it has been reported that Salmonella infected plants are asymptomatic, wilting, yellowing, biomass loss and a hypersensitive response (HR) have recently been demonstrated in plant tissues. The aim of this study was to investigate tissue response to different strains of S. enterica in two varieties of cactus as well as the persistence of Salmonella strains in the tissue. The top of pads or cladodes (20-25 cm) of greenhouse-grown (at 17.3 degree C and 39.8% RH, average) “Milpa Alta” and Atlixco varieties were inoculated with water or 1 mL 8.0 log CFU of strains S. Typhimurium (N4), S. javiana (N7) which were both isolated from Opuntia ficus-indica, and S. Typhimurium ATCC23564 (Sal 4). There were 20 cladodes per cactus variety with evaluations every 24 h for 5 days starting 4 h after inoculation for visual symptoms and persistence in the tissue determined according to SSA1-1994-NOM-109 and Madigan et al. (2001). Data was subjected to analysis of variance with mean separation by Tukey’s (? = 0.05) test. Color and appearance changed in longitudinal sections of pads of both varieties only in the area where the bacteria were infiltrated and this could be considered a hypersensitive response. All three Salmonella strains persisted 48 h or longer.

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