Human-specific phages infecting Enterococcus host strain MW47: Are they reliable microbial source tracking markers?

Aim: The aim of this study was to determine the morphological diversity and environmentalsurvival of human-specific phages infecting Enterococcus faecium host strain MW47, tosupport their use as microbial source tracking (MST) markers. Methods and Results: Twenty phages capable of infecting strain MW47 were propagatedand their morphologies determined using transmission electron microscopy (TEM), whichrevealed that a heterogeneous group of phages was able to infect strain MW47. Three distinctmorphologies from two different families (Myoviridae and Siphoviridae) were observed. Insitu inactivation experiments were subsequently conducted to determine their environmentalpersistence. Conclusion: The findings revealed a statistically significant link between morphology andthe rate of inactivation, with phages belonging to the Myoviridae family demonstrating morerapid inactivation in comparison to those belonging to the Siphoviridae family. Significance and Impact of Study: The results suggest that whilst Enterococcus MW47phages appear to be a potentially valuable MST tools, significant variations in the persistenceof the different phages mean that the approach should be used with caution, as this mayadversely affect the reliability of the approach, especially when comparing MW47 phagelevels or presence across different matrices (e.g. levels in sediments or shellfish). Thishighlights the importance of elucidating the ecological characteristics of newly proposedMST markers before they are used in full-scale MST investigations.