Resistance to disinfection emerges in Salmonella Typhimurium following cyclic exposure to 3-(diethylamino)propylamine

Cleaning and disinfection (C&D) of food-contact surfaces is an essential measure to prevent microbial contamination during food processing. These procedures commonly involve the use of biocides to reduce or eliminate foodborne pathogens such as Salmonella spp. Among the available biocides, amines such as 3-(diethylamino)propylamine (DEAPA) have gained attention for their broad-spectrum activity and high efficacy in the presence of organic matter. However, it remains unclear whether these biocides can exert selective pressure and promote resistance development, potentially affecting the effectiveness of current C&D procedures. In this study, three adaptive laboratory evolution (ALE) protocols representing different exposure patterns were applied to evaluate the emergence of DEAPA-resistant variants (RVs). This approach resulted in seven independently evolved RVs, which were subsequently characterised phenotypically and genetically. The most tolerant RVs showed a 10,000-fold increase in survival after exposure to 13,000 mg/L DEAPA for 15 min, a 1000-fold increase in survival after heat treatment at 54 °C for 30 min, and reduced susceptibility to gentamicin, with an MIC exceeding 2 mg/L. Genetic analysis identified mutations in genes involved in metabolism ( adhE, cyaA , and atpF ), signal transduction ( crp ), transport ( corA ), and cell motility ( cheZ and fliF ), suggesting that resistance emerged through genetic adaptation affecting multiple cellular functions. These findings show that repeated DEAPA exposure, particularly through cyclic lethal treatments, can select Salmonella Thyphimurium variants with increased DEAPA tolerance under laboratory conditions. Further studies under representative industrial conditions are required to assess the potential risk associated with the emergence of these variants.