Biological characteristics and comparative genomics of five Klebsiella phage isolates

Abstract:

[Objective] As a major pathogen of human infection, multidrug-resistant Klebsiella poses a great challenge in clinical treatment. To provide more scientific data for the application of phages, we analyzed and compared the biological and genomic characteristics of several strains of Klebsiella phages. [Methods] Klebsiella phages were isolated from human and animal fresh feces and sewage by the double plate method. The phage morphology was observed by phosphotungstic acid staining and transmission electron microscopy. The host spectrum, thermal stability, and pH stability of the phages were measured, and the one-step growth curve and in vitro bacteriostatic curve were established. The comparative genomics analysis was carried out for the whole genomes of the phage isolates. We further evaluated the protective effect of the phage isolates by the survival rate of Galleria mellonella larvae infected with the multidrug-resistant mutant Klebsiella variicola BS375-3 in vivo. [Results] The five phage isolates belonged to Schitoviridae (pKP-BM327-1.2), Autographiviridae (pKP-M186-2.1, pKP-M186-2.2, and pKV-BS375-3.1), and Drexlerviridae (pKP-BS317-1.1). The phage isolates pKV-BS375-3.1 and pKP-BM327-1.2 could lyse eight and three bacterial hosts, respectively, while pKP-M186-2.1, pKP-M186-2.2, and pKP-BS317-1.1 could only lyse one bacterial host. The five phage isolates entered the exponential growth stage 10-20 min after inoculation and maintained stable activity at -20 ℃-37 ℃ and pH 6-10. The survival rate of G. mellonella larvae infected with the K. variicola BS375-3 treated with pKV-BS375-3.1 (MOI=100) reached 80% (8/10) after 96 h. The genomes of the five phage isolates had the length of 42-77 kb and did not carry resistance genes or virulence genes. The traceability analysis based on endolysin showed that the protein demonstrated diversity in Klebsiella phages and was conserved within the genus. [Conclusion] All the five Klebsiella phage isolates had good antibacterial activity in vitro and stable biological characteristics. The endolysins of the phage isolates were conserved within the genus. The phage pKV-BS375-3.1 with a wide host range and short latency has a potential application prospect in the clinical treatment of Klebsiella pneumoniae and K. variicola infections.