Evidence of association of salmonellae with tomato plants grown hydroponically in inoculated nutrient solution

Abstract

The possibility of uptake of salmonellae by roots of hydroponically grown tomato plants was investigated. Within 1 day of exposure of plant roots to Hoagland nutrient solution containing 4.46 to 4.65 log(10) CFU of salmonellae/ml, the sizes of the pathogen populations were 3.01 CFU/g of hypocotyls and cotyledons and 3.40 log(10) CFU/g of stems for plants with intact root systems (control) and 2.55 log(10) CFU/g of hypocotyls and cotyledons for plants from which portions of the roots had been removed. A population of > or =3.38 log(10) CFU/g of hypocotyls-cotyledons, stems, and leaves of plants grown for 9 days was detected regardless of the root condition. Additional studies need to be done to unequivocally demonstrate that salmonellae can exist as endophytes in tomato plants grown under conditions that simulate commonly used agronomic practices.

FIG. 1.

DNA-based typing of presumptive Salmonella colonies isolated from tomato plants grown in Hoagland solution inoculated with a five-serotype mixture of pathogens. Lane 1, 100-bp DNA marker; lanes 2 through 6, DNA profiles of Salmonella serotype Enteriditis, Salmonella serotype Hartford, Salmonella serotype Michigan, Salmonella serotype Poona, and Salmonella serotype Montevideo, respectively; lanes 7 through 10, profiles of isolates from inoculated Hoagland solution; lanes 11 through 14, profiles of isolates from the hypocotyls and cotyledons of tomato plants on day 9; lanes 15 through 18, profiles of isolates from stems of tomato plants on day 9; lanes 19 through 22, profiles of isolates from leaves of tomato plants on day 9.