Abstract
The novel virulent Siphoviridae bacteriophage swi2 was isolated from a pig farm, and its biological characteristics, genome architecture, and infection-related properties were characterized. Phage swi2 has a high titer of 1.01 × 1012 PFU/mL with good tolerance to UV rays and remains stable in the pH range of 6–10 and at temperatures less than 50°C. One-step growth analysis revealed that phage swi2 had a 25 min latent period with a large burst size (1,000 PFU/cell). The biological characteristics indicated that swi2 had good host infectivity and effective lytic activities. The genome of phage swi2 is composed of 47,611 bp with a G + C content of 46.50%. Eighty-nine orfs were predicted, and only 18 of them have known functions. No virulence genes or drug resistance genes were found in the genome. Genome sequence comparison of phage swi2 showed that there were a total of 10 homologous phages in the database with low similarity (less than 92.51% nucleotide identity and 66% query coverage). The predicted host lysis-related genes of phage swi2 consist of one holin, two endolysins, and Rz/Rz1 equivalents. Antibacterial activity assays showed that both endolysins could naturally reduce the host Escherichia coli 51 titers by -1 log unit both in vitro and in vivo, EDTA showed no obvious synergistic action, and holin had no lytic effects on the host cell. These results provide necessary information for the development of antibiotic alternatives for the treatment of multidrug-resistant Escherichia coli infection.
Highlights
Escherichia coli (E. coli) is widely distributed in the environment as one of the most important opportunistic pathogens and can cause colibacillosis of swine, which seriously threatens animal health globally, especially in high-density breeding farms (Tran et al, 2018)
The E. coli 51 strain was selected as the host cell to test the biological characterization of phage swi2
Quantitative fluorescent PCR was used to test the phage swi2 titer, the results showed that the copy number of recombinant plasmid pColdTF-lysin1-SYBR was 6.15 × 1013 copies/mL and established the standard curve y = −3.086x + 42.852, the titer of phage swi2 showed similar results (Supplementary Figure 1)
Summary
Escherichia coli (E. coli) is widely distributed in the environment as one of the most important opportunistic pathogens and can cause colibacillosis of swine, which seriously threatens animal health globally, especially in high-density breeding farms (Tran et al, 2018). Phages and their enzymes have become a hot topic in the field of developing antibiotic substitutes, and there have been many successful phage therapy reports regarding the prevention and treatment of bacterial infections, suggesting that phages are good candidates as antibiotic alternatives (Vahedi et al, 2018). A bacteriophage (phage) with a broad host range, efficient proliferation, a high lysis titer and stable physical is more dominant in the prevention and control of colibacillosis. In this way, it can avoid the failure of prevention and control in the process of phage preparation to prevent and control bacterial infections based on the mismatch between the lysis range and the host bacteria (Alemayehu et al, 2012). Limited lysins have been reported that show bactericidal activity against gram-negative bacteria, it showed that the ability of lysins to pass bacterial outer membrane is mediated by the naturally occurring sequence of two ends (residues 1–20) carrying positively charged or hydrophobic residues (Plotka et al, 2019; Lai et al, 2020; Wang et al, 2020)
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