Bacteriophages specifically recognizing the lipopolysaccharide antigens O4, O5, O6, and O7 of Escherichia coli

Four bacteriophages recognizing the Escherichia coli lipopolysaccharide (LPS) antigens O4, O5, O6, and O7, respectively, were isolated from pooled sewage samples. Electron microscopic investigations revealed icosahedral phage structures. Phages phi O4, phi O5, and phi O7 belonged to Bradley's morphology group C, while phi O6 had a tail and resembles phages of group A of Bradley. The nucleic acid of the phages was identified as double-stranded DNA of different genomic sizes. Host range studies showed that only E. coli strains with homologous O antigens were attacked. No lysis of encapsulated and rough E. coli strains was observed. The phages specifically depolymerized the homologous LPS of their host strains; they may be useful for detecting respective non-capsulated E. coli strains in epidemiological studies as simple alternative to the laborious serological typing. Diagnostic application is restricted, however, as strains carrying K antigens have not been detected. The high specificity of the phage-associated enzymes provides a mild method for the preparation of oligosaccharides from the LPS for structural studies.