Phage Biology

Except in a few cases where phages are being used therapeutically, little has been published about their host ranges on different strains of a given bacterial species. A substantial fraction of the phages isolated for potential therapeutic purposes belong morphologically to the broad T-even family. In addition, there have been more phylogenetic and physiological studies carried out for Escherichia coli than for any other bacteria. Despite this, no general host-range comparison has been done with any of these phages on E. coli. With coliform bacteria being a major cause of diarrheal disease, it makes sense to explore our current phage resources while continuing to build upon them.

Three years ago, our lab reported the testing of nearly 100 T-even phages from various collections on about 100 bacterial isolates, showing a wide range of infectivity patterns. This included strains from food, pig pathogens, E. coli and Shigella lab strains and most of the 72 strains in the classic E. coli collection of reference (ECOR). Enzyme typing has been used to develop an extensive phylogenetic tree for all of the ECOR strains. Upon examination of the host ranges of the different T-even-type phages on the ECOR collection, it became clear that there is no direct relationship between patterns of phage infectivity and bacterial phylogenetic groups. This supports the idea that the ability of phage to infect is determined largely by surface receptors, which do not necessarily correspond to the phylogenic grouping of bacteria.

While most of the ECOR strains were infected by a number of these phages, some were hit by very few. Thus, in addition to studying the growth of phages under conditions approaching those in the natural environment, we have specifically isolated phages against the bacteria that were virtually uninfected. The five host strains chosen for the selection -- ECOR 1, 26, 41, 43 and 72 -- represent four of the five ECOR phylogenetic groups. We wanted to determine whether these bacteria were somehow inherently resistant, as well as find phages that could complement the existing collections in developing cocktails for therapeutic trials.

We had no trouble isolating phages from local sewage against any of the five ECOR strains. These phages represent a variety of plaque morphologies, and each infect up to 3 of the 5 strains. We will present data on two of these isolates (TLP and TL2) that infect a variety of strains and have small plaque sizes, indicative that they are relatively large phages. Of these, TL2 is morphologically of the T-even family, does well anaerobically and makes phage that are stable in lysates. TLP is also a myoviridae but is significantly larger than T4.

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Last Updated: May 29, 2008

The Evergreen State College

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