Listeria monocytogenes and Salmonella adapted to vegetable surfaces may enhance their stress resistance

Listeria monocytogenes, Salmonella, adapted pathogens, stress resistance Foodborne pathogens colonize vegetable surfaces, where cells are exposed to desiccation, cold temperatures and nutrient limitations. This adaptation may alter their stress resistance. Fresh cut lettuce or whole cherry tomatoes were inoculated (6 log CFU/cm2) with three strains of L.monocytogenes serotypes 1/2a, 4b or Salmonella serovars Typhimurium, Enteritidis and incubated for 1 or 5 days at 5?C. Adapted cells were harvested and exposed in TrypticSoy Broth to (i) pH 3.5 (lactate, acetate or HCl) and pH 1.5 (HCl) for 6 h; (ii) 20% NaCl for 14 days and (iii) 60 ?C for 150 sec. L. monocytogenes grown overnight (TSBYE) at 30 ?C or Salmonella at 37?C (TSB) and at 5 ?C for 1 or 5 days were used as in vitro controls. Adaptation to lettuce for 1 day sensitized L. monocytogenes to pH 3.5 compared to control (30 ?C); however after 5 days, resistance of cells to acetic acid and pH 1.5 increased (p <0.05). Cells adapted on tomato surface survived at pH 1.5 for 5 h, while control cells only for 1 h. During osmotic stress, cells habituated on tomato surface for 5 days reduced to <0.7 log CFU/ml after 14 days, while those habituated for 1 day after 8 days; lettuce-adapted and control cells survived only for 4 days. Under thermal stress, tomato-adapted cells decreased below the limit of 0.7 log CFU/ml, while control cells and those adapted to lettuce remained at 2.5 log CFU/ml after 150 sec. Salmonella adapted to lettuce or tomato surface, didn?t survive after one day in 20% NaCl, whereas control cells (37?C) survived for 10 days. The ability of pathogens to adapt to vegetables may enhance their stress tolerance, therefore special attention should be paid on the management of postharvest safety of produce. Original title, complete list of authors, and sources:ADAPTATION TO VEGETABLE SURFACES ALTERS THE RESISTANCE OF LISTERIA MONOCYTOGENES AND SALMONELLA TO ACIDIC, OSMOTIC AND THERMAL STRESSPoimenidou, S.; Chatzithoma, D.N.; Paramythiotis, S.; Hatjilouka, A. and Skandamis, P. pskan@aua.grLaboratory of Food Quality Control & Hygiene, Department of Food Science & Technology, Agricultural University of Athens, GreeceCAMA 2013, XI International Controlled & Modified Atmosphere Research Conference, Trani (Italy), 3-7 June. Picture: L. monocytogenes 3D model. Source: www.http://www.turbosquid.com/3d-models/microbes-micro-organisms-3d-model/644726