Characterization of bacteriophages specific to drug resistant Pseudomonas aeruginosa isolated from wastewater

The emergence of drug resistant Pseudomonas aeruginosa has become a global concern because its infections cannot be cured by most of presently used antibiotics. In the midst of finding alternative therapeutic approaches to control drug resistant bacteria, bacteriophage therapy is considered as a most promising one. The aims of this study are to isolate and classify bacteriophages specific to drug resistant P.aeruginosa SH01 and to examine their ability to inhibit its specific bacterial host in vitro when used individually or as mixtures of more than one bacteriophage. In this study 3 bacteriophages, WS-23, WS-40 and WS-45, were isolated from different wastewater sources and found to produce small clear plaques of 1-2 min in diameter. All of then inhibited only drug resistant P.aeruginosa SH01, but not other bacteria used in this study. Their genomes were digested by various restriction enzymes including including EcoRI, HindIII, KpnI and PstI. As revealed by transmission electron microscopy, each of the bacteriophage had an isometric head with a contractile tail. Based on their genomic and morphological characteristics, all of the 3 bacteriophages were classified as members in the family Myoviridae. From one-step growth curves, the bacteriophages WS-23, WS-40 and WS-45 had latent periods of 30, 40 and 40 min, respectively, burst periods of 180, 150 and 180 min, respectively, and burst sizes of 45, 76 and 30 PFU/infected cell, respectively. When each bacteriophage was used to inhibit P.aeruginosa SH01 in vitro, it was found that the bacteriophages WS-23, WS-40 and WS-45 reduced the bacterial cells by 3, 6 and 6 log CFU/ml, respectively as compared to the control treatment (no bacteriophage added). However, inhibitory activity of the mixtures of 2 bacteriophages (WS-23 plus WS-40, WS-23 plus WS-45 and WS-40 and WS-45) and 3 bacteriophage (WS-23, WS-40 and WS-45) was weaker than that of single bacteriophage. Further investigation is required to explain the decrease of inhibitory activity when these bacteriophages are used together. In conclusion, bacteriophages obtained from this study were able to inhibit drug resistant P.aeruginosa SH01; hence, they may be useful as therapeutic agents to treat diseases caused by the bacterium.