The coexistence of Escherichia coli serotype O157:H7 and its specific bacteriophage in continuous culture

For the development of phage therapy, systematic understanding mechanisms of bacteriophage resistance will be required. We describe a new strain of Escherichia coli O157:H7, named MUL, which stably co-exists with the O157:H7-specific lytic bacteriophage PP01 Chemostat cultures of E coli O157:H7 infected with PP01 showed unchanging cell concentration, but phage concentrations which increased by similar to10(8) PFU mL(-1). However, the latent period, burst size, and growth rate of MUL were the same as in a PP01-susceptible strain. The binding rate of PP01 to the cell surface was diminished 8.5-fold in Mu(L). By observation of the binding of fluorescently labeled O157:H7-specific phage to individual Mu(L) cells, we found that clonal Mu(L) cultures were heterogeneous in their ability to bind bacteriophage. 15% of the Mu(L) population was completely resistant to PP01 infection. Mu(L) also co-existed with bacteriophages unrelated to PP01 Broad-range phage resistance by clonal heterogeneity represents a new class of bacteria-phage interactions. (C) 2004 Federation of European Microbiological Societies. Published by Elsevier B.V.. All rights reserved.