Effects of bactericides on Salmonella survival on the surface of and in inoculated tomato leaves

Authors: Gu, Ganyu; MURPHY, CLAIRE - Virginia Tech; HAMILTON, ALEXIS - Virginia Tech; ZHENG, JIE - Food And Drug Administration(FDA); Nou, Xiangwu; RIDEOUT, STEVEN - Virginia Tech; STRAWN, LAURA - Virginia Tech

Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2023
Publication Date: 1/30/2023
Citation: Gu, G., Murphy, C., Hamilton, A., Zheng, J., Nou, X., Rideout, S., Strawn, L. 2023. Effects of bactericides on Salmonella survival on the surface of and in inoculated tomato leaves. Journal of Food Safety. https://doi.org/10.1111/jfs.13043.
DOI: https://doi.org/10.1111/jfs.13043

Interpretive Summary: Consumption of raw tomatoes has been attributed to 15 multistate outbreaks of salmonellosis between 1973 through 2010. In a collaborated study with VT and FDA, we tried to address a central question that agricultural industry personnel have queried regarding the feasibility of bactericide applications for reducing Salmonella contamination risks. Results indicated that PAA and streptomycin significantly reduced Salmonella population on the surface of inoculated tomato leaves one day after treatment. However, the effect did not influence Salmonella population inside inoculated leaves. Salmonella reduction in tomato leaves was detected one day after copper hydroxide application. Salmonella did not grow on the surface of, or in tomato leaves after bactericide application during the 8 d study duration. Data from this study can be used by producers to improve the management strategies on the mitigation of Salmonella contamination risks during tomato production in fields.

Technical Abstract: Several outbreaks of Salmonellosis have been traced back to contaminated tomato. The produce production environment poses a risk for Salmonella contamination; however, little is known about the effects of pest management practices on Salmonella concentrations. The study objective was to evaluate bactericide application on the recovery of Salmonella on the surface of, and in tomato leaves. Thirty tomato plants were grown in a greenhouse and inoculated with S. enterica serovars Newport or Typhimurium. Inoculation was performed by dipping tomato leaves in an 8 log CFU/mL Salmonella suspension with 0.025% (v/v) Silwet L-77 for 30 s. Plants were treated with one of four bactericides, each with a different mode of action [acibenzolar-S-methyl, copper hydroxide, peroxyacetic acid (PAA) and streptomycin]. Bactericides were applied at manufacturers’ labeled rate. Salmonella was enumerated at 0.125 (3 h), 2, 6, and 9 d post-inoculation (dpi), and counts were log transformed. Growth of Salmonella was not observed during the experiment. At 2 dpi, PAA and streptomycin significantly reduced Salmonella concentrations on the surface of inoculated tomato leaves (ca. 0.7 and 0.6 log CFU/g, respectively; P=0.05), while copper hydroxide significantly reduced Salmonella concentrations in tomato leaves (ca. 0.8 log CFU/g; P=0.05), compared to the control. No significant differences in Salmonella concentrations were observed on or in tomato leaves from 2 to 9 dpi, regardless of bactericide application. These findings suggest that while bactericide applications resulted in reductions of Salmonella concentrations on or in tomato leaves, single in-field bactericide applications may not be an effective mitigation strategy in limiting potential Salmonella contamination. Future research, including multiple in-field bactericide applications, or bactericide use in combination with other mitigation strategies may offer intriguing management practices to limit possible preharvest contamination.