Specific detection of Escherichia coli using a phage-assisted ß-galactosidase assay

Abstract

Fast and reliable detection of microbial contaminants in food, water and environmental samples is critical for an efficient public health management. Most available methods provide good results although many of them have a number of drawbacks ranging from low sensitivity to the need of sophisticated equipment, the use of expensive reagents or the participation of highly skilled personnel. This work describes an easy to implement method for the detection of E. coli in liquid samples using a robust non-specific ß-galactosidase assay made highly selective through the use of a specific T4 lytic phage as a permeabilization reagent. The assay is performed in 96 well plates using MUG (4-methylumberlliferyl-ß-D-galactopyranoside) as the enzyme substrate and has a total length of 90 minutes. The method is able to detect 75 cells of E. coli. Under the conditions of the assay this corresponds to a concentration of 1.49·103 cells·mL− 1 of sample. For the analysis of field samples, we produced an extended version of the assay that incorporates preconcentration and preincubation steps with a total running length of 7.5 hours. When tested with field samples and compared with Colilert-18 the method performed well, with a limit of detection of 96 cells·100 mL− 1.