bluephage, a fast method for the detection of the viral fecal indicators, somatic coliphages, in water

Somatic coliphages have been proposed as indicators of fecal and viral pollution in water and food as one of the most suitable methods in terms of reliability, reproducibility, and cost effectiveness. several countries propose to include or have already included them in their water management policies. standardized methods (iso, epa) for their enumeration are available, but their implementation in routine laboratories will be definitely easier if user-friendly commercial kits become available. this study presents a newly developed method for the evaluation of somatic coliphages. the method based in the use of a tailored escherichia coli host strain that allows detection of less than 10 somatic coliphages in less than 3:30 h, well below the ordinary working hours in a day. the genetically engineered host strain wg5 presents a replacement of uidb and uidc genes encoding the transport of the glucuronic acid inside the cell, and overexpression of uida, encoding the enzyme β-glucoronidase. because of the inability of the strain to incorporate the substrate inside the cell, the substrate only reaches the enzyme after the lysis of the bacterial cells caused by phages. after phage-mediated lysis, the intracellular accumulated enzyme is released to the medium producing a change of color from yellow to green-blue. the modified host strain recovers the same number of phages than the wild type strain. the sensitivity and rapidness of the method allows results to be obtained within 1:30 h for concentrations of 500 - 50 phages and 2:15 h for samples with 5 phages. incubation temperatures ranging from 30ºc to 44ºc provided results at the same times. in contrast, at 20ºc and 25ºc the results needed more time to come out.the method is applicable to different types of liquid and solid samples and to different volumes the qualitative positive/negative results can be used for quantitative analysis applying the most probable number (mpn). bluephage is the fastest microbiological method detecting culturable microorganisms for the determination of fecal pollution reported so far.