Evaluating the Use of Divalent Cations to Improve F+ Coliphage Detection (2014)
Undergraduates: Emeraghi David, Yvonne Yuen and Rachel Nethery
Faculty Advisor: Mark Sobsey
Department: Health Environmental Sciences & Engineering
Background: Recreational waters can be contaminated by pathogens found in the fecal matter of humans and animals. These pathogens can cause gastrointestinal illness at a very low doses and it is difficult and costly to detect these pathogens in recreational waters. Therefore, indicator organisms that are abundant in the intestinal tracts of humans and animals are used as surrogates to indicate potential fecal contamination. Male-specific (F+) coliphages are viruses that infect E.coli and are used as viral indicators because they are morphologically and functionally similar to enteric virus, prevalent in wastewater and the intestinal tracts of humans and animals. EPA Method 1601 is a standard method used for detecting coliphages in water. However, the current method does not include divalent cations in spot plates, which are hypothesized to facilitate coliphage attachment and/or nucleic acid transfer to E.coli hosts. To test this hypothesis, MgCl2 or CaCl2 were added to spot plates as divalent cations and results were compared to spot plates with no divalent cations. Method: A total of 165 seawater samples were analyzed with EPA Method 1601. Samples were analyzed with spot plates containing no divalent cations, 0.01M MgCl2, 0.02M, 0.01M, and 0.002M CaCl2. Results: Among all spot plate divalent cations conditions tested, 0.01M MgCl2 had the highest level of coliphage detection, followed by 0.01M, 0.002M and 0.02M CaCl2 and lastly no divalent cation. Conclusions: Adding MgCl2 or CaCl2 as divalent cations to spot plates significantly increased F+ coliphage detection. Spot plates with MgCl2 had the highest level of detection. EPA Method 1601 should be revised to include divalent cations in spot plates for improved F+ coliphage detection.