Characterization of a Novel Pseudomonas psychrophila Phage P-2FD and Its Endolysin

Pseudomonas is a common food spoilage bacterium that can cause spoilage of milk, eggs, fish, and other food products under low temperature conditions. In this study, a total of four Pseudomonas phages were isolated from spoiled fish and shrimp, and the biological characterization of one of them, Pseudomonas psychrophila phage P-2FD, which exhibited a wider host spectrum, was carried out. Morphological analyses showed that phage P-2FD belonged to the Podoviridae family and the Caudovirales order. When the multiplicity of infection (MOI) was 1000, the growth of P. psychrophila was almost completely inhibited before 9 h. When phage P-2FD treated P. psychrophila in grass carp with an MOI of 1000, the bacterial counts were reduced by 1.77 log₁₀ CFU/g compared with the control group at 4°C for 96 h, indicating that phage P-2FD effectively inhibited the growth of P. psychrophila. Genomic analysis showed that P-2FD was a novel phage, and the whole genome length of P-2FD was 40,453 bp with 42 open reading frames (ORFs). The phage endolysin LysP-2FD was expressed in Escherichia coli BL21 (DE3) and purified, and the lytic rate against P. psychrophila was 78.17% at a concentration of 20 μmol/L. The present study suggests that phage P-2FD and endolysin can be used as potential antimicrobial agents for the control of P. psychrophila in the food industry.