Isolation and Characterization of Three Lytic Bacteriophages to Overcome Multidrug-, Extensive Drug-, and Pandrug-Resistant Pseudomonas aeruginosa.

Background: The worrisome spread of multidrug-resistant (MDR) pathogens necessitates research on nonantibiotic therapeutics. Among these therapeutics, phage treatment uses bacteriophages (phages) as alternative antimicrobial agents.

Objectives: This project evaluates the lytic efficiency of phage cocktails in vitro versus MDR, extensive drug-resistant (XDR), and pandrug-resistant (PDR) P. aeruginosa isolates.

Methods: We utilized host range and genetic information to generate a three-phage cocktail capable of killing multiple clinical strains of P. aeruginosa and examined the effectiveness of the cocktail in this study. The isolates (114) had variable resistance to 13 antibiotics. A phage-enrichment approach was used to purify the bacteriophage cocktail; a phage lysate with a high titer (5 × 10⁹ PFU/mL) was prepared and tested against 114 P. aeruginosa isolates.

Findings: The results showed that a cocktail of three phages (MMS1, MMS2, and MMS3) could lyse P. aeruginosa in both planktonic liquid and dish cultures. The MMS cocktail phages were shown to be viable between 4 and 50°C at pH 4-9. A one-step growth curve showed that the MMS phages had a latent period of 15 min and a burst period of approximately 18 min based on the size of approximately 265 offspring phages per host cell. The MMS3 phage was sequenced and shown to lack genes associated with bacterial pathogenicity or antibiotic resistance.

Conclusions: Notably, XDR and PDR isolates were sensitive to the phage cocktail, a prospective substitute for antibiotics that does not contribute to the growth of antibiotic resistance, suggesting that the phage cocktail might be useful for generating personalized phage therapeutics.