Complete genome sequence of the novel phage vB_EcoS_PHB17, which infects Shiga-toxin-producing Escherichia coli.

The complete genome of the novel phage vB_EcoS_PHB17, which infects Shiga-toxin-producing Escherichia coli, was sequenced, revealing a linear double-stranded DNA genome of 48,939 bp with 46% GC content and protruding 150-bp 5' cohesive termini. The genome contained 85 open reading frames, 28 of which were annotated with known functions. No tRNA-encoding genes were detected. Phylogenetic analysis suggested that phage PHB17 is a novel phage of family Siphoviridae.

Biological characteristics and genome analysis of a novel phage vB_KpnP_IME279 infecting Klebsiella pneumoniae.

Klebsiella pneumoniae (family Enterobacteriaceae) is a gram-negative bacterium that has strong pathogenicity to humans and can cause sepsis, pneumonia, and urinary tract infection. In recent years, the unreasonable use of antibacterial drugs has led to an increase in drug-resistant strains of K. pneumoniae, a serious threat to public health. Bacteriophages, viruses that infect bacteria, are ubiquitous in the natural environment. They are considered to be the most promising substitute for antibiotics because of their high specificity, high efficiency, high safety, low cost, and short development cycle. In this study, a novel phage designated vB_KpnP_IME279 was successfully isolated from hospital sewage using a multidrug-resistant strain of K. pneumoniae as an indicator. A one-step growth curve showed that vB_KpnP_IME279 has a burst size of 140 plaque-forming units/cell and a latent period of 20 min at its optimal multiplicity of infection (MOI = 0.1). Phage vB_KpnP_IME279 survives in a wide pH range between 3 and 11 and is stable at temperatures ranging from 40 to 60 °C. Ten of the 20 strains of K. pneumoniae including the host bacteria were lysed by the phage vB_KpnP_IME279, and the multilocus sequence typing and wzi typing of the 10 strains were ST11, ST37, ST375, wzi209, wzi52, and wzi72, respectively. The genome of vB_KpnP_IME279 is 42,518 bp long with a G + C content of 59.3%. Electron microscopic observation showed that the phage belongs to the family Podoviridae. BLASTN alignment showed that the genome of the phage has low similarity with currently known phages. The evolutionary relationship between phage vB_KpnP_IME279 and other Podoviridae was analyzed using a phylogenetic tree based on sequences of phage major capsid protein and indicates that the phage vB_KpnP_IME279 belongs to the Podoviridae subfamily. These data enhance understanding of K. pneumoniae phages and will help in development of treatments for multidrug-resistant bacteria using phages.

Protective and therapeutic application of the depolymerase derived from a novel KN1 genotype of Klebsiella pneumoniae bacteriophage in mice.

Klebsiella pneumoniae is one of the major Gram-negative bacterial pathogens causing hospital-acquired multidrug-resistant infections, and the antimicrobial treatment options are scarce. The lack of available antimicrobials has prompted the development of alternative strategies for the treatment of these infections. In this study, a K. pneumoniae bacteriophage (vB_KpnP_IME321) targeting a KN1 capsular type strain, Kp409, was isolated, characterized and sequenced. This bacteriophage has a latent period of 20 min and a burst size of approximately 410 pfu/cell. It contained 49 predicted open reading frames, of which ORF42 was identified as encoding the putative capsule depolymerase. The enzyme expressed and purified in the Escherichia coli BL21 system, namely Dp42, could depolymerize the capsular polysaccharide of Kp409 and form translucent halos on the plates. The phage-encoded depolymerase could increase the inhibitory effect of serum on the growth of bacteria in vitro. Pre-treated with Dp42 rescued 100% of mice following lethal Kp409 challenge, and administration of this enzyme after infection significantly increased survival rates of infected mice in the animal experiment. In conclusion, the phage-encoded depolymerase Dp42 represents a potential alternative strategy for controlling infections mediated by K. pneumoniae expressing the KN1 capsular polysaccharide.