A generally more efficient way of isolating lytic phages from marine environments is by the use of enrichment cultures. In this approach, the prefiltered water sample that is to be screened for phages against a given target bacterium, is enriched with a bacterial growth medium and amended with that target bacteria (Eisenstark 1967; Carlson 2005). This allows any lytic phages present in the sample to infect the target bacteria and propagate in the cultures, and subsequently, be isolated and purified. The two main advantages of the enrichment approach are 1) that it allows for screening for phages in a much larger volume of sample (typically 25–50 mL, rather than 5–10 µL), thus increasing the probability of isolating rare phages, and 2) that it allows the combination of different target hosts (e.g., different strains of a specific bacteria of interest) in the same incubation, again increasing the possibility of phage isolation.