Biofilm production and resistance to disinfectants in Salmonella strains isolated from prickly pear, water, and soil.

Authors: SANTOS VILLAMIL, ALFRECIA - Campus Montecillo; HERNANDEZ ANGUIANA, ANA MARA - Campus Montecillo; ALBERTO ESLAVO CAMPO, CARLOS - Campus Montecillo; LANDA SALGADO, PATRICIA - Campus Montecillo; MORA AGUILERA, GUSTAVO - Campus Montecillo; Luchansky, John

Submitted to: Revista Mexicana de Ciencias Agricolas
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2012
Publication Date: 12/1/2012
Citation: Santos Villamil, A., Hernandez Anguiana, A., Alberto Eslavo Campo, C., Landa Salgado, P., Mora Aguilera, G., Luchansky, J.B. 2012. Biofilm production and resistance to disinfectants in Salmonella strains isolated from prickly pear, water, and soil. Revista Mexicana de Ciencias Agricolas. 3:1063-1074.

Interpretive Summary: Prickly pear, also known as nopal, is a native cactus specie of appreciable economic importance in Mexico. This plant or its by-products are typically ingested fresh as a salad or processed into juice or yogurt, but it can also be used as a dietary supplement or be formulated into cosmetics. Because of its widespread production and consumption/uses, it was of interest to determine the association, if any, of target pathogens, such as Salmonella spp., with fresh cactus stems and associated soil and water samples. Salmonella can form biofilms, which in turn can become sources of contamination in the production of food. Within biofilms Salmonella resist treatment with antibiotics and are difficult to remove in normal cleaning procedures. We recovered Salmonella associated with nopal at relatively high frequency. Although all strains displayed the ability to form biofilms in vitro, there were significant differences in their abilities to do so. Treatment of biofilms containing Salmonella with the common disinfectants citric acid, lactic acid, and sodium hypochlorite inhibited the pathogen. These data represent the first to establish the capacity for Salmonella isolated from nopal to form biofilms, a characteristic of concern from a public health perspective for people who may consume fresh nopal, and highlight the importance of using disinfectants as an intervention for control of Salmonella on nopal.

Technical Abstract: The objectives of this study were to: i) determine the capacity of Salmonella isolated from prickly pear (10 strains), water samples (2 strains), and soil (3 strains) to form biofilms, and ii) evaluate the bactericidal effect of citric acid, lactic acid, and sodium hypochlorite on biofilm-forming strains. We used a published method and polystyrene plates with a minimal essential medium containing glucose (MEM) and determined the optical density (OD) to estimate the production of biofilms. The disinfectants were applied to plates with biofilm formation in simple MEM for 48 h at 37 deg C. All strains showed biofilm production after 24 h, although there were significant differences (Tukey alpha = 0.05), depending on the incubation time with respect to the OD. The soil strains expressed biofilm capacity faster than the strains recovered from water and prickly pear. Sodium hypochlorite (200 ppm) and lactic acid (1.5 x 10 to the -4 power) inhibited cell growth when applied for 20 min on biofilms. These results demonstrated the importance of implementing good agricultural practices in the production of prickly pear as a strategy to prevent contamination by Salmonella and the subsequent formation of biofilm in vivo, where the effect of treatment with sanitizers may vary.