ISOLATION AND IDENTIFICATION OF TWO LYTIC PHAGES AGAINST VIBRIO PARAHAEMOLYTICUS

The aim of this study was to screen lytic phase and provide new alternatives for the prevention and control of V. parahaemolyticus. In this study, two lytic phages SX-2 and SX-F were isolated by double-layer plate method against the host bacteria V. parahaemolyticus Vp13. The morphological structures of these two phages were observed by transmission electron microscope (TEM). The types of nucleic acids were identified by the degradation characteristics of DNase I, RNase A, Mung Bean Nuclease and Hind Ш. The lysis spectrum, optimal multiplicity of infection and one step growth curve of SX-2 and SX-F were also analyzed. The results of TEM showed that the capsid protein of lytic phage of SX-2 was a complex symmetry with icosahedral symmetry head that had length of about 110 nm and width of about 50 nm and a spiral symmetry tail that had length of about 110 nm and width of about 10 nm. SX-F showed hexagon with length of about 56.86 nm and width of about 50.74 nm without a tail, which was icosahedral symmetry. Both SX-2 and SX-F were linear double stranded DNA bacteriophage. They were belonged to the family of Myoviri-dae and Tectivirus based on the taxonomy standard of the ninth report of the International Committee Taxonomy of Viru-ses. Results of lytic experiment on 85 Vibrio strains showed that phage SX-2 could lysis 23 strains of V. parahaemolyticus and one strain of Vibrio alginolyticus, and phage SX-F could lysis 19 strains of V. parahaemolyticus and one strain of V. alginolyticus. The optimal multiplicity of infection of plase SX-2 and SX-F were 0.0001. One step growth curve showed that the incubation period of phage SX-F was about 10min, the lytic cycle was 70min, and the burst size was 116.2. The incubation period of the phage SX-2 was less than 10min, and the lytic cycle was about 70min, and the burst size was 209.3. These results indicated that both of them were lytic phages, which can be used as an alternative to control and prevention of the V. parahaemolyticus.