Isolation and Characterization of Lytic Bacteriophage Against Multi-drug Resistant Pseudomonas aeruginosa.

BACKGROUND: Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen frequently causing healthcare-associated infections. The apocalyptic rise of antimicrobial resistance has rekindled interest in age-old phage therapy that uses phages (viruses that infect bacteria) to kill the targeted pathogenic bacteria. Because of its specificity, phages are often considered as potential personalized therapeutic candidate for treating bacterial infections. METHODS: In this study, we isolated and purified lytic phages against multi-drug resistant P. aeruginosa using soft agar overlay technique. Phage characteristics like thermal and pH stability, latent period and burst size were determined using one-step growth assay while multiple host range spectrum was determined by spot assay. The phages were further characterized using protein profiling. RESULTS: Three Pseudomonas phages (øCDBT-PA31, øCDBT-PA56 and øCDBT-PA58) were isolated from the holy rivers of Kathmandu valley. Among 3 phages, øCDBT-PA31 demonstrated multiple host range and could lyse multi-drug resistant strain of P. aeruginosa. Further, øCDBT-PA31 showed latent period of 30 minutes with corresponding burst sizes of 423-525 PFU/cell. Interestingly, øCDBT-PA31 also tolerated a wide range of adverse conditions, such as high temperature (50°C) and pH 3-11. Further, protein profiling revealed that øCDBT-PA31 has 4 and øCDBT-PA11 had 3 distinct bands in the gradient gel ranging from approximately 3.5-29 kilodaltons (kDa) suggesting them to be morphologically distinct from each other. CONCLUSIONS: As multi-drug resistant bacteria are emerging as a global problem, lytic phages can be an alternative treatment strategy when all available antibiotics fail.

Pharmacokinetics and Pharmacodynamics of a Novel Virulent Klebsiella Phage Kp_Pokalde_002 in a Mouse Model.

Phage therapy is one of the most promising alternatives to antibiotics as we face global antibiotic resistance crisis. However, the pharmacokinetics (PK) and pharmacodynamics (PD) of phage therapy are largely unknown. In the present study, we aimed to evaluate the PK/PD of a locally isolated virulent novel øKp_Pokalde_002 (Podoviridae, C1 morphotype) that infects carbapenem-resistant Klebsiella pneumoniae (Kp56) using oral and intraperitoneal (IP) route in a mouse model. The result showed that the øKp_Pokalde_002 rapidly distributed into the systemic circulation within an hour via both oral and IP routes. A higher concentration of phage in plasma was found after 4 h (2.3 x 105 PFU/ml) and 8 h (7.3 x 104 PFU/ml) of administration through IP and oral route, respectively. The phage titer significantly decreased in the blood and other tissues, liver, kidneys, and spleen after 24 h and completely cleared after 72 h of administration. In the Kp56 infection model, the bacterial count significantly decreased in the blood and other organs by 4-7 log10 CFU/ml after 24 h of øKp_Pokalde_002 administration. Elimination half-life of øKp_Pokalde_002 was relatively shorter in the presence of host-bacteria Kp56 compared to phage only, suggesting rapid clearance of phage in the presence of susceptible host. Further, administration of the øKp_Pokalde_002 alone in healthy mice (via IP or oral) did not stimulate pro-inflammatory cytokines (TNF-α and IL-6). Also, treatment with øKp_Pokalde_002 resulted in a significant reduction of pro-inflammatory cytokines (TNF-α and IL-6) caused by bacterial infection, thereby reducing the tissue inflammation. In conclusion, the øKp_Pokalde_002 possess good PK/PD properties and can be considered as a potent therapeutic candidate for future phage therapy in carbapenem-resistant K. pneumoniae infections.

Therapeutic Efficacy of Bacteriophage Therapy to Treat Carbapenem Resistant Klebsiella Pneumoniae in Mouse Model.

BACKGROUND: Global emergence of carbapenem-resistant Klebsiella pneumoniae is a major public health concern. Phage therapy - application of lytic phage to kill pathogenic bacteria - is considered as one of the promising alternatives to tackle this antibiotic crisis in recent days. This study aimed to isolate, characterize and evaluate therapeutic efficacy of a novel K. pneumoniae phage in mouse model. METHODS: A novel lytic bacteriophage (phage) Kp_Pokalde_002 was isolated against carbapenem-resistant K. pneumoniae (Kp56) and characterized. Safety parameters of the phage were evaluated by bioinformatic analysis of its genome. A lethal dose (~1×107 CFU/mouse) of Kp56 was determined and administrated in the mice. The infected mice were treated with phage Kp_Pokalde_002 at a multiplicity of infection (MOI) 1.0 (~1×107 PFU/mouse) via both oral and intraperitoneal (IP) routes. RESULTS: Isolated phage comprised an icosahedral capsid with a short tail. Based on genome analysis, the phage was strictly lytic belonging the Podoviridae family (T7-like viruses) and free from any virulent and antibiotic-resistant genes. The phage was stable up to 60 °C for 30 minutes and effective between pH 4 to 11 (optimum pH 9). The phage exhibited a short latent period (20 minutes) with burst size of 121 phage particles per infected cell. The infected mice were rescued with the phage therapy via both oral and IP route. Significant reduction of bacterial load (3-7 log10 CFU/ml) in the blood and lung was observed in the treatment group. CONCLUSIONS: We provide an evidence of successful phage therapy against carbapenem-resistant K. pneumoniae infected mouse model using locally isolated lytic phage.