Abstract:

Objective To isolate enterohemorrhagic E. coli O157 phages from raw sewage and to investigate the biological characteristics of isolated phages and to provide experimental basis for the development of a biologic agent against enterohemorrhagic E.coli O157. Methods  Bacteriophages were isolated from raw sewage and were identified by plaque methods using enterohemorrhagic E.coli O157 as host cells. After purification ofphages with ultrafitration,the size and morphology of phages were examined by electron microscope,and the multiplicity of infection and growth curve of phages were carried out by mean of host bacteria and phages mixture in different portions. The structural and nonstructural proteins of phages were analyzed by SDS-PAGE electrophoresis. The extracted genomes of phages were digested with restriction enzymes. Results The results of electron microscope showed that the head of phages exhibited a spherical form,40 nm in diameter and these phages ha
d a tail,about 80 nm in length. The multiplicity of infection of phages was 10^-2,that was,when the ratio of host bacteria to phages being 1∶100,the most efficient lysis. The growth curve of phages revealed that the incubation was 10 min,the outbreak of the time was 30 min and the lysis amount was 130. SDS-PAGE anal
ysis showed that 13 kinds of proteins of phages were found and their relative molecular mass were 16 000-20 000. Electrophoresis of DNA showed that the size of the genome of phages was 23 000 bp. Conclusion A strain of bacteriophages againstenterohemorrhagic E. coli O157 is isolated and characterized,and it is lytic and highly specific to E. coli O157. According to the biologic features,enterohemorrhagic E. coli O157 phages are classified into Caudovirales,Siphoviridae.

Key words: enterohemorrhagic Escherichia coli O157;bacterophages;multiplicity of infection