# Differential survival and tolerance mechanisms of Bacillus subtilis and Salmonella Enteritidis under slightly acidic electrolyzed water stress

## TL;DR

Slightly acidic electrolyzed water kills harmful Salmonella but spares beneficial Bacillus bacteria, offering a safe food disinfection method.

## Contribution

The study reveals how SAEW selectively inactivates pathogens while preserving probiotics through differential stress responses.

## Key findings

- Bacillus subtilis survives SAEW stress while Salmonella Enteritidis is inactivated.
- B. subtilis recovers rapidly after SAEW exposure, unlike S. Enteritidis.
- SAEW triggers divergent stress responses, with B. subtilis upregulating antioxidant enzymes.

## Abstract

Salmonella Enteritidis (S. Enteritidis) is a major foodborne pathogen, and its effective control is critical for food safety. Although slightly acidic electrolyzed water (SAEW) is widely adopted as an eco-friendly bactericidal agent in food systems, its impact on beneficial microbiota remains poorly characterized, despite their importance for food quality. To address this gap, we systematically compared SAEW tolerance between Bacillus subtilis (B. subtilis, a model probiotic) and S. Enteritidis in monoculture and co-culture systems. Notably, B. subtilis retained viability at 70 mg/L ACC (from 7.82 to 3.99 log CFU/mL, P < 0.05), whereas S. Enteritidis was completely inactivated at 40 mg/L. In co-culture, B. subtilis maintained consistently higher viable counts (P < 0.05), demonstrating a significant survival advantage under SAEW stress. Furthermore, B. subtilis demonstrated rapid recovery in co-culture, attaining 8.0 log CFU/mL within 32 h post-exposure, while S. Enteritidis was eradicated. Mechanistically, SAEW disrupted membrane integrity in both strains but triggered divergent stress responses: S. Enteritidis exhibited significant ROS accumulation (P < 0.05), ATP depletion (P < 0.05), and suppressed the activities of key antioxidant enzymes (P < 0.05). Conversely, B. subtilis showed significant upregulation of these enzymes (SOD, CAT, GSH-Px, P < 0.05) with stable ROS levels. Consequently, SAEW enables selective pathogen inactivation while preserving probiotic strains, supporting its targeted application in food systems.

The increasing adoption of slightly acidic electrolyzed water (SAEW) as an eco-friendly disinfectant in food safety highlights the need for a deeper understanding of its selective bactericidal mechanisms. This study addresses a critical gap in the literature by demonstrating that SAEW effectively targets harmful pathogens, such as Salmonella Enteritidis, while preserving beneficial probiotics, such as Bacillus subtilis. By elucidating the differential stress responses of these microorganisms, our findings provide valuable insights into the ecological dynamics of food systems. The ability of SAEW to selectively inactivate pathogens without disrupting beneficial microbiota supports its targeted application in enhancing food safety and quality. This research not only advances the scientific understanding of SAEW’s mechanisms but also has practical implications for developing safer food preservation methods, ultimately contributing to public health and food security.