Abstract

Citrobacter freundii is a kind of pathogen widely existing in environment and human gut, and its drug resistance has been reported in recent years. The objective of this study was to isolate a phage targeting Citrobacter freundii and explore its morphological, biological and genomic characteristics to help the control and antibacterial of Citrobacter freundii. The Citrobacter freundii strain was co-cultured with sewage samples, followed by doublelayer plate assays to isolate a phage specific to Citrobacter freundii. Subsequently, the biological and genomic characteristics of the isolated phage were studied. As a result, a phage with strong stability of Citrobacter freundii was isolated from sewage and named CPB1126. The transmission electron microscopy revealed that CPB1126 presents as a Myoviridae-like morphology, characterized by a polyhedron-shaped head measuring 112±6.2 nm in length and 81±5.4 nm in width, along with a tail measuring of 103±3.7 nm in length. The optimal number of infection is 0.1. The one-step growth curve showed that the incubation period lasts 20 min and the outbreak period lasts 20 min. In addition to its isolated host, a Citrobacter werkmanii ATCC51114 strain was also sensitive to CPB1126. CPB1126 exhibited strong stability. It is resistant to chloroform and maintains high activity at pH 3-10. It also maintains high activity at temperature from -20° to 55°. The antibacterial experiments showed that excellent antibacterial effects could be achieved between 0.1 and 10 multiplicity of infection. The total length of the genome is 172 165 base pairs with 302 coding sequences. The functional annotation ratio is 56.3 %, it is classified as the Caudoviricetes order, Straboviridae family, Tevenvirinae subfamily, Moonvirus genus. CPB1126 is the 4^th reported isolated phage of genus of Moonvirus, and its tail protein sequence is <85 % similar to that of reported phages of the same genus. In conclusion, this study reports the isolation of a highly virulent Citrobacter phage exhibiting robust lytic capabilities and strong stability, which would contribute to the accumulation of phage isolates resources and provides great assets for future phage usage especially for infections.