Reduction of Enteric Pathogens in Bottled Water Using Residual Ozone

Ozone is an effective and safe disinfectant used globally in the bottled water industry. Ozone infusion at a high level helps maintain a residual level (0.1–0.4 mg/L) at the time of bottling, thus can ensure 4 log microbial reductions. This study validated the efficacy of residual ozone against Escherichia coli O157:H7, non-O157 Shiga toxin-producing E. coli (STEC; O26, O45, O103, O111, O121, O145), and Salmonella Typhimurium. A pilot-scale ozone system infused 0.5 L polyethylene terephthalate (PET) bottles with ozonated water (0.1–0.4 mg/L). Pathogens were inoculated into samples (∼6 or 4 log CFU/mL) immediately after ozonation treatment, followed by incubation at 25 °C for 5–180 min. Additional trials evaluated the isolated effect of pH (5.0, 7.0, and 9.0) and total dissolved solids (TDS; 5, 50, and 500 mg/L) at a fixed ozone concentration (0.1 mg/L ozone) and contact time (30 min). Posttreatment samples were neutralized (0.1% sodium thiosulfate), filtered, and plated on Petri films for enumeration (35 °C, 48 h). Neutralization (0.1% sodium thiosulfate) was validated to have no antimicrobial effect in controls. All pathogens exhibited ≥4 log reductions across ozone concentrations (0.1–0.4 mg/L), contact times (≥5 min), and inoculum levels (6 or 4 log CFU/mL). Extended contact (30–180 min) did not enhance reduction. However, at 500 mg/L TDS, reductions fell below 4 logs: Salmonella (2.60 log ± 1.24), E. coli O157:H7 (1.72 log ± 1.10), and non-O157 STEC (2.74 log ± 1.45). Similarly, pH 5.0 and 9.0 resulted in <4 log reductions. While residual ozone effectively achieves microbial safety benchmarks, elevated TDS and nonneutral pH significantly impair efficacy. These findings underscore the necessity of monitoring water quality parameters to optimize ozone disinfection in bottled water facilities, ensuring consistent compliance with food safety standards.