GROWTH AND SURVIVAL OF SALMONELLA-MONTEVIDEO ON TOMATOES AND DISINFECTION WITH CHLORINATED WATER

The survival on tomato fruits (Lycopersicum esculentum) of a rifampici n-resistant strain of Salmonella montevideo (Centers for Disease Contr ol and Prevention [CDC] isolate G4639), the alleged source of the 1993 multistate outbreak of salmonellosis, was affected by inoculum dose a nd inoculation site (unbroken surface or wounds and stem scars), as we ll as by the medium (distilled water, Butterfield's buffer, or tryptic ase soy broth [TSB]) used to deliver the bacterium. This bacterium ino culated at 4 log(10) CFU (colony-forming units) per site in distilled water survived for 20 h on tomato skin. However, comparable survival o ccurred at the stem scars and growth cracks with smaller inoculum dose s (3 log(10) CFU). The bacterial populations increased rapidly on punc ture wounds and tomato slices but decreased on the unbroken surface an d stem scar. With unbroken skin and approximately 4 log(10) CFU per si te, the population survived for at least 48 h but could not be consist ently detected after 5 days. By contrast, the stem scar population sur vived for at least 7 days and decreased only 1 to 2 log(10) units. The inherently low pH of the tomatoes did not inhibit bacterial growth. T reatment with 100 ppm of aqueous chlorine for up to 2 min failed to ki ll all bacteria at these inoculation sites. This was especially true w hen the bacterial suspensions were prepared in TSB. TSB supported bett er bacterial survival and/or growth and also protected against the bac tericidal effect of aqueous chlorine.