Characterization and Genomic Analyses of Pseudomonas aeruginosa Podovirus TC6: Establishment of Genus Pa11virus

LysSYL: a broad-spectrum phage endolysin targeting Staphylococcus species and eradicating S. aureus biofilms

BACKGROUND

Staphylococcus aureus and its single or mixed biofilm infections seriously threaten global public health. Phage therapy, which uses active phage particles or phage-derived endolysins, has emerged as a promising alternative strategy to antibiotic treatment. However, high-efficient phage therapeutic regimens have yet to be established.

RESULTS

In this study, we used an enrichment procedure to isolate phages against methicillin-resistant S. aureus (MRSA) XN108. We characterized phage SYL, a new member of the Kayvirus genus, Herelleviridae family. The phage endolysin LysSYL was expressed. LysSYL demonstrated stability under various conditions and exhibited a broader range of efficacy against staphylococcal strains than its parent phage (100% vs. 41.7%). Moreover, dynamic live/dead bacterial observation demonstrated that LysSYL could completely lyse MRSA USA300 within 10 min. Scan and transmission electron microscopy revealed evident bacterial cell perforation and deformation. In addition, LysSYL displayed strong eradication activity against single- and mixed-species biofilms associated with S. aureus. It also had the ability to kill bacterial persisters, and proved highly effective in eliminating persistent S. aureus when combined with vancomycin. Furthermore, LysSYL protected BALB/c mice from lethal S. aureus infections. A single-dose treatment with 50 mg/kg of LysSYL resulted in a dramatic reduction in bacterial loads in the blood, liver, spleen, lungs, and kidneys of a peritonitis mouse model, which resulted in rescuing 100% of mice challenged with 108 colony forming units of S. aureus USA300.

CONCLUSIONS

Overall, the data provided in this study highlight the strong therapeutic potential of endolysin LysSYL in combating staphylococcal infections, including mono- and mixed-species biofilms related to S. aureus.

Isolation of a bacteriophage targeting Pseudomonas aeruginosa and exhibits a promising in vivo efficacy

Pseudomonas aeruginosa is an important pathogen that causes serious infections. Bacterial biofilms are highly resistant and render bacterial treatment very difficult, therefore necessitates alternative antibacterial strategies. Phage therapy has been recently regarded as a potential therapeutic option for treatment of bacterial infections. In the current study, a novel podovirus vB_PaeP_PS28 has been isolated from sewage with higher lytic activity against P. aeruginosa. Isolated phage exhibits a short latent period, large burst size and higher stability over a wide range of temperatures and pH. The genome of vB_PaeP_PS28 consists of 72,283 bp circular double-stranded DNA, with G + C content of 54.75%. The phage genome contains 94 open reading frames (ORFs); 32 for known functional proteins and 62 for hypothetical proteins and no tRNA genes. The phage vB_PaeP_PS28 effectively inhibited the growth of P. aeruginosa planktonic cells and displayed a higher biofilm degrading capability. Moreover, therapeutic efficacy of isolated phage was evaluated in vivo using mice infection model. Interestingly, survival of mice infected with P. aeruginosa was significantly enhanced upon treatment with vB_PaeP_PS28. Furthermore, the bacterial load in liver and kidney isolated from mice infected with P. aeruginosa and treated with phage markedly decreased as compared with phage-untreated P. aeruginosa-infected mice. These findings support the efficacy of isolated phage vB_PaeP_PS28 in reducing P. aeruginosa colonization and pathogenesis in host. Importantly, the isolated phage vB_PaeP_PS28 could be applied alone or as combination therapy with other lytic phages as phage cocktail therapy or with antibiotics to limit infections caused by P. aeruginosa.

Isolation and Characterization of Pseudomonas aeruginosa Phages with a Broad Host Spectrum from Hospital Sewage Systems and Their Therapeutic Effect in a Mouse Model

This study aimed to isolate and characterize phages as an alternative treatment of multidrug- or pan-drug-resistant Pseudomonas aeruginosa. Phage titers and bacterial densities correlated, with the phages disappearing after bacteria were eliminated. We isolated phages in filtered sewage water by a double-layered agar spot test. Fifty-eight P. aeruginosa strains were used to screen the host spectrum of the 14 phages isolated. Random amplification of polymorphic DNA-typing polymerase chain reaction was used to analyze the genomic homologies of the 58 host bacteria strains and four phages with a broad host spectrum. Transmission electron microscopy was used to observe the morphology of the four phages with a broad host spectrum. Mice with intraabdominal P. aeruginosa infection were used as an in vivo animal model to investigate the therapeutic effect of the selected phage. Four virulent phages with a broad host spectrum specific to P. aeruginosa strains were isolated. They were all double-stranded DNA viruses and belonged to four different genotypes. The test curve showed that phage I had the highest adsorption rate, the shortest latent period, and the largest burst size. The infected mouse model indicated that small doses of phage I could prevent the death of infected mice. Phage titers and bacterial densities correlated, with phages disappearing after bacteria were eliminated. Phage I was the most effective and promising treatment of drug-resistant P. aeruginosa.

Isolation and Characterization of the First Zobellviridae Family Bacteriophage Infecting Klebsiella pneumoniae

In order to address the upcoming crisis in the treatment of Klebsiella pneumoniae infections, caused by an increasing proportion of resistant isolates, new approaches to antimicrobial therapy must be developed. One approach would be to use (bacterio)phages and/or phage derivatives for therapy. In this study, we present a description of the first K. pneumoniae phage from the Zobellviridae family. The vB_KpnP_Klyazma podovirus, which forms translucent halos around the plaques, was isolated from river water. The phage genome is composed of 82 open reading frames, which are divided into two clusters located on opposite strands. Phylogenetic analysis revealed that the phage belongs to the Zobellviridae family, although its identity with the closest member of this family was not higher than 5%. The bacteriophage demonstrated lytic activity against all (n = 11) K. pneumoniae strains with the KL20 capsule type, but only the host strain was lysed effectively. The receptor-binding protein of the phage was identified as a polysaccharide depolymerase with a pectate lyase domain. The recombinant depolymerase protein showed concentration-dependent activity against all strains with the KL20 capsule type. The ability of a recombinant depolymerase to cleave bacterial capsular polysaccharides regardless of a phage's ability to successfully infect a particular strain holds promise for the possibility of using depolymerases in antimicrobial therapy, even though they only make bacteria sensitive to environmental factors, rather than killing them directly.

Current knowledge in the use of bacteriophages to combat infections caused by Pseudomonas aeruginosa in cystic fibrosis

Pseudomonas aeruginosa (PA) is considered the first causal agent of morbidity and mortality in people with cystic fibrosis (CF) disease. Multi-resistant strains have emerged due to prolonged treatment with specific antibiotics, so new alternatives have been sought for their control. In this context, there is a renewed interest in therapies based on bacteriophages (phages) supported by several studies suggesting that therapy based on lytic phages and biofilm degraders may be promising for the treatment of lung infections in CF patients. However, there is little clinical data about phage studies in CF and the effectiveness and safety in patients with this disease has not been clear. Therefore, studies regarding on phage characterization, selection, and evaluation in vitro and in vivo models will provide reliable information for designing effective cocktails, either using mixed phages or in combination with antibiotics, making a great progress in clinical research. Hence, this review focuses on the most relevant and recent findings on the activity of lytic phages against PA strains isolated from CF patients and hospital environments, and discusses perspectives on the use of phage therapy on the treatment of PA in CF patients.

Isolation and characterization of two homolog phages infecting Pseudomonas aeruginosa

Bacteriophages (phages) are capable of infecting specific bacteria, and therefore can be used as a biological control agent to control bacteria-induced animal, plant, and human diseases. In this study, two homolog phages (named PPAY and PPAT) that infect Pseudomonas aeruginosa PAO1 were isolated and characterized. The results of the phage plaque assay showed that PPAT plaques were transparent dots, while the PPAY plaques were translucent dots with a halo. Transmission electron microscopy results showed that PPAT (65 nm) and PPAY (60 nm) strains are similar in size and have an icosahedral head and a short tail. Therefore, these belong to the short-tailed phage family Podoviridae. One-step growth curves revealed the latent period of 20 min and burst time of 30 min for PPAT and PPAY. The burst size of PPAT (953 PFUs/infected cell) was higher than that of PPAY (457 PFUs/infected cell). Also, the adsorption rate constant of PPAT (5.97 × 10⁻⁷ ml/min) was higher than that of PPAY (1.32 × 10⁻⁷ ml/min) at 5 min. Whole-genome sequencing of phages was carried out using the Illumina HiSeq platform. The genomes of PPAT and PPAY have 54,888 and 50,154 bp, respectively. Only 17 of the 352 predicted ORFs of PPAT could be matched to homologous genes of known function. Likewise, among the 351 predicted ORFs of PPAY, only 18 ORFs could be matched to genes of established functions. Homology and evolutionary analysis indicated that PPAT and PPAY are closely related to PA11. The presence of tail fiber proteins in PPAY but not in PPAT may have contributed to the halo effect of its plaque spots. In all, PPAT and PPAY, newly discovered P. aeruginosa phages, showed growth inhibitory effects on bacteria and can be used for research and clinical purposes.

Characterization of the Bacteriophage BUCT603 and Therapeutic Potential Evaluation Against Drug-Resistant Stenotrophomonas maltophilia in a Mouse Model

Stenotrophomonas maltophilia (S. maltophilia) is a common opportunistic pathogen that is resistant to many antibiotics. Bacteriophages are considered to be an effective alternative to antibiotics for the treatment of drug-resistant bacterial infections. In this study, we isolated and characterized a phage, BUCT603, infecting drug-resistant S. maltophilia. Genome sequencing showed BUCT603 genome was composed of 44,912 bp (32.5% G + C content) with 64 predicted open reading frames (ORFs), whereas no virulence-related genes, antibiotic-resistant genes or tRNA were identified. Whole-genome alignments showed BUCT603 shared 1% homology with other phages in the National Center for Biotechnology Information (NCBI) database, and a phylogenetic analysis indicated BUCT603 can be classified as a new member of the Siphoviridae family. Bacteriophage BUCT603 infected 10 of 15 S. maltophilia and used the TonB protein as an adsorption receptor. BUCT603 also inhibited the growth of the host bacterium within 1 h in vitro and effectively increased the survival rate of infected mice in a mouse model. These findings suggest that bacteriophage BUCT603 has potential for development as a candidate treatment of S. maltophilia infection.

Characterization and genome analysis of Pseudomonas aeruginosa phage vB_PaeP_Lx18 and the antibacterial activity of its lysozyme

A lytic Pseudomonas aeruginosa phage, vB_PaeP_Lx18 (Lx18), was isolated from the sewage of a dairy farm. Biological characterization revealed that Lx18 was stable from 40 °C to 60 °C and over a wide range of pH values from 4 to 10. It was able to lyse 63.6% (21/33) of the P. aeruginosa strains tested and was able to reduce and disperse biofilms, with a biofilm reduction rate of 76.8%. Whole-genome sequencing showed that Lx18 is a dsDNA virus with a genome of 42,735 bp and G+C content of 62.16%. The genome contains 54 open reading frames (ORFs), 28 of which have known functions, including DNA replication and modification, transcriptional regulation, structural and packaging proteins, and host cell lysis. No virulence or tRNA genes were identified. Phylogenetic analysis showed that phage Lx18 belongs to the genus Phikmvvirus. The lysozyme of Lx18, Lys18, was cloned and expressed. The combined action of Lys18 and ethylenediaminetetraacetic acid (EDTA) had antibacterial activity against Pseudomonas aeruginosa. The study of phage Lx18 and its lysozyme will provide basic information for further research on the treatment of Pseudomonas aeruginosa infections.

Characterization of a Lytic Bacteriophage against Pseudomonas syringae pv. actinidiae and Its Endolysin

Pseudomonas syringae pv. actinidiae (Psa) is a phytopathogen that causes canker in kiwifruit. Few conventional control methods are effective against this bacterium. Therefore, alternative approaches, such as phage therapy are warranted. In this study, a lytic bacteriophage (PN09) of Psa was isolated from surface water collected from a river in Hangzhou, China in 2019. Morphologically, PN09 was classified into the Myoviridae family, and could lyse all 29 Psa biovar 3 strains. The optimal temperature and pH ranges for PN09 activity were determined as 25 to 35 ∘C and 6.0 to 9.0, respectively. The complete genome of PN09 was found to be composed of a linear 99,229 bp double-stranded DNA genome with a GC content of 48.16%. The PN09 endolysin (LysPN09) was expressed in vitro and characterized. LysPN09 was predicted to belong to the Muraidase superfamily domain and showed lytic activity against the outer-membrane-permeabilized Psa strains. The lytic activity of LysPN09 was optimal over temperature and pH ranges of 25 to 40 ∘C and 6.0 to 8.0, respectively. When recombinant endolysin LysPN09 was combined with EDTA, Psa strains were effectively damaged. All these characteristics demonstrate that the phage PN09 and its endolysin, LysPN09, are potential candidates for biocontrol of Psa in the kiwifruit industry.

Genome-Wide Identification and Analysis of Chromosomally Integrated Putative Prophages Associated with Clinical Klebsiella pneumoniae Strains

Klebsiella pneumoniae, an opportunistic pathogen found in the environment and human mucosal surfaces, is a leading cause of nosocomial infections. K. pneumoniae is now considered a global threat owing to the emergence of multidrug-resistant strains making its infections untreatable. In this study, 254 strains of K. pneumoniae were screened for the presence of prophages using the PHASTER tool. Very few strains lacked prophages (3.1%), while the remaining harboured both intact (811) and defective prophages (709). A subset of 42 unique strains of K. pneumoniae was chosen for further analysis. Our analysis revealed the presence of 110 complete prophages which were further classified as belonging to Myoviridae (67.3%), Siphoviridae (28.2%) and Podoviridae family (4.5%). An alignment of the 110 complete, prophage genome sequences clustered the prophages into 16 groups and 3 singletons. While none of the prophages encoded for virulence factors, 2 (1.8%) prophages were seen to encode for the antibiotic resistance-related genes. The CRISPR-Cas system was prevalent in 10 (23.8%) out of the 42 strains. Further analysis of the CRISPR spacers revealed 11.42% of the total spacers integrated in K. pneumoniae chromosome to match prophage protein sequences.

Characterization and genome sequencing of a novel T7-like lytic phage, kpssk3, infecting carbapenem-resistant Klebsiella pneumoniae

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has spread globally and emerged as an urgent public health threat. Bacteriophages are considered an effective weapon against multidrug-resistant pathogens. In this study, we report a novel lytic phage, kpssk3, which is able to lyse CRKP and degrade exopolysaccharide (EPS). The morphological characteristics of kpssk3 observed by transmission electron microscopy, including a polyhedral head and a short tail, indicate that it belongs to the family Podoviridae. A one-step growth curve revealed that kpssk3 has a latent period of 10 min and a burst size of 200 plaque-forming units (pfu) per cell. kpssk3 was able to lyse 25 out of 27 (92.59%) clinically isolated CRKP strains, and it also exhibited high stability to changes in temperature and pH. kpssk3 has a linear dsDNA genome of 40,539 bp with 52.80% G+C content and 42 putative open reading frames (ORFs). No antibiotic resistance genes, virulence factors, or integrases were identified in the genome. Based on bioinformatic analysis, the tail fiber protein of phage kpssk3 was speculated to possess depolymerase activity towards EPS. By comparative genomics and phylogenetic analysis, it was determined that kpssk3 is a new T7-like virus and belongs to the subfamily Autographivirinae. The characterization and genomic analysis of kpssk3 will promote our understanding of phage biology and diversity and provide a potential strategy for controlling CRKP infection.