Clearing zones on lawns of host bacteria potentially contain all lytic phages against the given host that were present in the original water sample. Little is still known about the occurrence and diversity of phages infecting specific hosts, but generally isolation procedures as those described above may reveal multiple phages against specific target bacteria (e.g., Comeau et al. 2006; Holmfeldt et al. 2007; Stenholm et al. 2008). It is therefore necessary to further isolate the phages to obtain specific stocks of single phages.