Real-time monitoring of E. coli O157 and Salmonella enterica serovar Typhimurium in water using ultrasound and latex-based immunoassay

Abstract

This study aimed at evaluating real-time, low-cost detection and quantification of bacteria, exemplified by E. coli O157 and Salmonella enterica serovar Typhimurium in aqueous systems. The approach takes advantage of the well-established latex-based immunoassay (LBI) and combines it with bacteria trapping and measuring using ultrasound. The results obtained demonstrate the utility of combining ultrasound standing waves of mean energy density 10 W cm⁻², acoustic amplitude 100 kPa, and a laminar flow rate of the medium of 60 μl min⁻¹ to trap selectively E. coli O157 or Salmonella enterica serovar Typhimurium (S. typhimurium) bacteria attached to 300–400 nm-antibody-coated latex particles. The ultrasound velocity measurements enabled a sensitivity down to 1.6 × 10⁴ colony-forming units (CFU) ml⁻¹ for E. coli O157 and 4.0 × 10⁴ CFU ml⁻¹ for S. typhimurium, compared to a sensitivity of 8.36 × 10⁵ CFU ml⁻¹ for E. coli O157 and 6.4 × 10⁶ CFU ml⁻¹ for S. typhimurium obtained by the standard LBI. The assay sensitivity can be further improved by use of various fluorescence methodologies.