Imidazole and methoxybenzylamine growth inhibitors reduce salmonella persistence in tomato plant tissues

Abstract

The control of Salmonella from farm to fork is challenging because of the lack of symptoms on contaminated fresh produce and the limited effectiveness of control methods before and after harvest. Therefore, the identification of new antimicrobials effective against Salmonella is needed to improve food safety. In this study, we investigated the activity of four anti-Salmonella small molecules (SMs; SM1, SM3, SM4, and SM5) on tomato tissues contaminated with Salmonella enterica subsp. enterica serotype Typhimurium (JSG626). No toxicity was detected on tomato seeds, seedlings, and fruits when tissues were treated with 200 µM SM. Moreover, SM1 and SM4 reduced (79 and 64%, respectively) the Salmonella Typhimurium population in tomato seedlings when sprayed on the leaves with two times the minimal bactericidal concentration (SM1=100 µM, SM3 and SM5= 50 µM, and SM=20 µM) at-1 and 3 days postinfection. The four SMs (200 µM) that have antagonistic effects on Salmonella had limited effect on the growth of beneficial plant bacteria (Bacillus amyloliquefaciens strain BA1 and Bacillus subtilis strain BS1, and Enterobacter sp. strain SM1796). SM1 and SM4, when combined with BA1 or SM1796, reduced the Salmonella Typhimurium population by at least 98.2% in tomato plants. The four SMs (at two times the minimal bactericidal concentration) also reduced the Salmonella Typhimurium population on the surface and inside contaminated green mature and ripe tomato fruits up to 95% after spraying or soaking the fruits in cold water for 30 min. The real-time in vivo imaging data showed that the stem abscission zone in fruits represents a major source of internalization and persistence of Salmonella Typhimurium against antimicrobials. The four SMs also displayed bactericidal effect on phytopathogens at 200 µM. This study demonstrates that these novel SMs could represent safe bactericides for control of Salmonella and phytopathogens in fresh produce and are compatible for use in combination with biocontrol agents. HIGHLIGHTS • Small molecules (SMs) 1, 3, 4, and 5 are novel growth inhibitors of Salmonella enterica. • These SMs are not toxic to tomato plant tissues including fruits. • Combining biocontrol agents and SMs enhanced the control of Salmonella in infected plants. • These SMs may be safe bactericides against Salmonella and phytopathogens in produce.