Detection of Escherichia coli in Drinking Water Using T7 Bacteriophage-Conjugated Magnetic Probe

In this study, we demonstrate a bacteriophage (phage)-based magnetic separation scheme for the rapid detection of Escherichia colt (E. coli) in drinking water. T7 phage is a lytic phage with a broad host range specificity for E. coli. Our scheme was as follows: (1) T7 bacteriophage-conjugated magnetic beads were used to capture and separate E. coli BL21 from drinking water; (2) subsequent phage-mediated lysis was used to release endemic beta-galactosidase (beta-gal) from the bound bacterial cells; (3) the release of beta-gal was detected using chlorophenol red-beta-D-galactopyranoside (CRPG), a colorimetric substrate which changes from yellow to red in the presence of beta-gal. Using this strategy, we were able to detect E. coli at a concentration of 1 x 10(4) CFU.mL(-1) within 2.5 h. The specificity of the proposed magnetic probes toward E. coli was demonstrated against a background of competing bacteria. By incorporating a pre-enrichment step in Luria-Bertani (LB) broth supplemented with isopropyl beta-D-thiogalactopyranoside (IPTG), we were able to detect 10 CFU.mL(-1) in drinking water after 6 h of pre-enrichment. The colorimetric change can be determined either by visual observation or with a reader, allowing for a simple, rapid quantification of E. coli in resource-limited settings.