Bacteriophage Lysis of Enterococcus Host Strains: A Tool for Microbial Source Tracking?

This paper describes the isolation of Enterococcus host strains, for potential use as simple bacteriophage (phage)-based microbial source tracking (MST) tools. Presumptive Enterococcus host strains were isolated from cattle feces, raw municipal wastewater, agricultural runoff, and waters impacted by farms or wastewater treatment works (WWTW) in southern England, United Kingdom (UK). All enterococcal host strains (n = 390) were first screened for their ability to detect phage in samples of raw municipal wastewater and fecal material from cattle, pigs, and sheep. Host strains that detected phage (n = 147) were ranked according to both their specificity to a particular fecal source and also the number of phages (expressed as plaque-forming units, PFU) that they detected per milliliter of sample. Host strains that demonstrated host specificity and which detected phages at levels greater than 100 PFU/mL (n = 29) were further tested using additional fecal samples of human and nonhuman origin. The specificity and sensitivity of the enterococcal host strains were found to vary, ranging from 44 to 100% and from 17 to 83%, respectively. Most notably, seven strains exhibited 100% specificity to either cattle, human, or pig samples. Isolates exhibiting specificity to cattle were identified as belonging to the species Enterococcus casseliflavus, Enterococcus mundtii, or Enterococcus gallinarum, while human and pig isolates were members of either Enterococcus faecium or Enterococcus faecalis. The high specificity of phages infecting Enterococcus hosts and the simplicity and relatively low cost of the approach collectively indicate a strong potential for using this method as a tool in MST.