Survival of Salmonella spp. and Pectobacterium carotovorum on Brush Roller Treated Tomatoes

Introduction: The brush roller method of washing tomatoes has been shown to be superior at removing Salmonella spp. from tomato surfaces, and uses less water and sanitizer compared to the flume method. However, little is known about the negative impacts that brushing may have on tomato surfaces, including potential abrasion, which may increase pathogen-harboring capacity. 

Purpose: To determine whether brush washing tomatoes increases the survivability of human (Salmonella spp.) or plant pathogens (Pectobacterium carotovorum) on tomatoes.

Methods: Mature green tomatoes were brush treated with water or 100 ppm NaOCl (pH 6.5) for 0, 15, or 60 s, then inoculated with rifampin-resistant Salmonella spp. or Pectobacterium at 8 log CFU/tomato and stored at 25°C 75-85 %RH for 7 days. To model survival on wounded fruit, other tomatoes were superficially punctured at 10 points then inoculated directly into the punctures with each culture independently (at either a 2 or 8 log CFU/tomato level) then stored under the same conditions. For all studies, tomatoes were sampled at days 0, 1, 3, and 7 using the rub-shake-rub method in 100 ml BPW, followed by plating on TSA+rifampin.

Results: Brush treatment did not have a significant impact on the survival of either pathogen; Salmonella and Pectobacterium populations decreased to below the detection limit of 2 log CFU/tomato within the first 3 days for all treatments. When wounded fruit were inoculated at low levels (2 log CFU/tomato), both cultures grew to and maintained near a 5.8 log CFU/tomato level. At high inoculation levels (8 log CFU/tomato), Salmonella cultures maintained near 8 log CFU/tomato for 7 days, whereas Pectobacterium grew to above 11 log CFU/tomato.

Significance: These results suggest that brush washing does not compromise tomato surfaces in such a way to allow enhanced survival of Salmonella spp. or Pectobacterium carotovorum.