The persistence of pathogenic Escherichia coli under acidic conditions poses a serious risk to food safety, especially in acidic foods such as kimchi. To identify the bacterial factors required for acid resistance, transcriptomic analysis was conducted on an acid-resistant enterotoxigenic E. coli strain and the genes with significant changes in their expression under acidic pH were selected as putative resistance factors against acid stress. These genes included those associated with a glutamatedependent acid resistance (GDAR) system and copper resistance. E. coli strains lacking GadA, GadB, or YbaST, the components of the GDAR system, exhibited significantly attenuated growth and survival under acidic stress conditions. Accordantly, the inhibition of the GDAR system by 3-mercaptopropionic acid and aminooxyacetic acid abolished bacterial adaptation and survival under acidic conditions, indicating the indispensable role of a GDAR system in acid resistance. Intriguingly, the lack of cueR encoding a transcriptional regulator for copper resistance genes markedly impaired bacterial resistance to acid stress as well as copper. Conversely, the absence of YbaST severely compromised bacterial resistance against copper, suggesting an interplay between acid and copper resistance. These results suggest that a GDAR system can be a promising target for developing control measures to prevent E. coli resistance to acid and copper treatments.

Contaminated produce has frequently been reported as a source of foodborne disease outbreaks worldwide for the past two decades [1]. Because vegetables and fruits are regarded as primary components of healthy nutrition, and are commonly consumed without thermal treatments, the safety of agricultural produce is critical for preventing and controlling associated foodborne diseases. However, food hygiene is challenged by the multifaceted survival strategies of enteric pathogens. Although enteric pathogens have evolved to survive and adapt to the hostile conditions within the gastrointestinal tract of their host species, they are also able to colonize plant surfaces by forming biofilms and thereby persist for long periods, which can subsequently lead to human infections via contaminated farm produce [2, 3]. Salmonella can also penetrate into the interior of plant tissues, exploiting plant stomata and trichomes as entry portals, and persist in the intercellular space [4-6]. Enteric pathogens contaminate soil and irrigation water via infected animal feces and in turn contaminate farm produce, exploiting plants as a vector for transmission between animal hosts [3, 7]. However, the bacterial determinants that enable enteric pathogens to adapt to unfavorable plant environments remain unclear. Therefore, in an effort to unveil the underlying mechanism of bacterial adaptation to plants, we investigated the comprehensive transcriptome of Salmonella enterica in contact with raw radish greens as a model system. Salmonella is a motile, gram-negative, rod-shaped genus belonging to the Enterobacteriaceae family, and one of the top 4 causes of diarrheal diseases that account for 70% of global foodborne diseases, including Escherichia coli, norovirus, Campylobacter, and Salmonella [8]. Salmonellosis commonly causes self-limiting gastroenteritis; however, life-threatening bacteremia, endovascular, and localized infections may occur depending on host health conditions and Salmonella serotypes [9]. The genus Salmonella consists of two species, S. enterica and S. bongori, and contains more than 2,500 different serotypes [9]. While all serotypes can cause diseases in humans, S. enterica serovars, including Typhimurium and Enteritidis, are the most notorious serotypes associated with Salmonella Salmonellosis is a form of gastroenteritis caused by Salmonella infection. The main transmission route of salmonellosis has been identified as poorly cooked meat and poultry products contaminated with Salmonella. However, in recent years, the number of outbreaks attributed to contaminated raw produce has increased dramatically. To understand how Salmonella adapts to produce, transcriptomic analysis was conducted on Salmonella enterica serovar Virchow exposed to fresh-cut radish greens. Considering the different Salmonella lifestyles in contact with fresh produce, such as motile and sessile lifestyles, total RNA was extracted from planktonic and epiphytic cells separately. Transcriptomic analysis of S. Virchow cells revealed different transcription...