Influence of phage population on the phage-mediated bioluminescent adenylate kinase (AK) assay for detection of bacteria

Aims: The effect of phage concentration on the activity of adenylate kinase (AK) released from the cells lysed during infection was investigated in order to optimize a bioluminescent phage-mediated method for bacterial enumeration. Methods and Results: The number of bacteria lysed by phages specific to Salmonella enteritidis and E. coli was determined using a bioluminescent method for the detection of AK released. In order to optimize the assay, the effect of phage concentration and time of infection on the amount of AK released was investigated. The release of AK was greatest at a multiplicity of infection (moi) of 10-100. Conclusions: The amount of AK released from Salmonella enteritidis and E. coli G2-2 cells by specific phages, SJ2 and AT20, respectively, depended on the type of bacteria, the stage of growth, the nature of phage, moi and time. Significance and Impact of the Study: An assay is described which allows detection of E. coli and Salmonella Enteritidis within 2 h at levels of 10(3) cfu ml(-1).