Since the TolA protein is structurally involved and essential for entry of filamentous bacteriophages (fd, f1 and M13) in E. coli[22], [39], the susceptibility of the ΔtolA mutant and the different TolA TR variants to infection with fd phage was compared by determining the phage plating efficiency (Table 1). The gene discussed is ELP1; the disease is infection.