Isolation and identification of plague phage from plague foci in Yulong County, Yunnan Province

Abstract

Objective To investigate whether the host animals of Yulong plague foci carry Yersinia pestis phage, and to identify isolated plague phage. Methods Rodent specimens were collected in 5 villages of Yulong plague foci in spring and autumn of 2016, respectively. Vaccine strain EV76 was used as breeding bacteria. Phage was isolated from the specimens by double-layer plate method and plaque morphology was identified. Results ① Totally 409 samples collected in spring failed in phage isolation. A total of 40 of Yersinia pestis phages were isolated from 444 samples in autumn, and the total isolation rate was 9.01% (40/444). ② The Yersinia pestis phages were isolated in all of 5 villages, and the isolation rate was of no significant difference (χ2= 5.055, P > 0.05). ③ Of the 40 strains of phage, 37 strains were isolated from Apodemus chevrieri, 2 strains from Eothenomys Miletus and 1 strain from Crocidura Dracula. ④Based on the appearance, the plaque of the phage was divided into three: large (diameter 1.5 - 2.5 mm), middle (0.5 - < 1.5 mm) and small (< 0.5 mm). Conclusion There is a higher number of plague phage in the host animals of the plague foci in Yulong County of Yunnan Province, the plaques are diverse in morphology, and their biological characteristics may be polymorphic. Key words: Yersinia pestis; Phage; Identification