Transfer of Salmonella montevideo onto the Interior Surfaces of Tomatoes by Cutting†

Abstract

Salmonella contamination of precut watermelon, tomatoes, and cantaloupes was responsible for several outbreaks of salmonellosis. To better understand the relationship between bacterial doses and their transfer onto cut surfaces by using a knife, rifampicin-resistant Salmonella montevideo at 7, 70, 700, or 7,000 CFU in Butterfield's buffer (BPB) or tryptic soy broth (TSB) was added to the stem scars of tomatoes. Tomatoes were cut from the stem scar to blossom end using a sterilized knife. After stem scars were aseptically removed, cut surfaces were placed on tryptic soy agar-rifampicin (TSA-RIF) plates or processed by a broth enrichment method to determine if S. montevideo had been transferred to the cut surface. S. montevideo was recovered in a dose-related fashion using both methods. A higher recovery rate was obtained with bacterial inocula in TSB than in BPB, and also with broth enrichment rather than the direct plating method. The distribution of the transferred S. montevideo on the cut surface of contaminated and noncontaminated tomatoes with a knife was related to the inoculum dose added to the stem scars. S. montevideo colonies were found to cluster at the stem scar region with the lower inoculum dose. However, when a higher inoculum dose was used, the colonies spread from the stem scar region to the center and bottom of cut tomatoes, or they were transferred to another uninoculated tomato by the contaminated knife. Therefore, the safety operation criteria recommended by FDA to wash fruits before cutting, to use clean and sanitized utensils and surfaces when preparing cut fruits, and to store the cut fruits below 7°C should be followed in preparing tomato slices to minimize salmonellosis outbreaks caused by this product.