Characterization and in vitro activity of a lytic phage RDN37 isolated from community sewage water active against MDR...

Due to the emergence of multidrug-resistant Uropathogenic E. coli (MDR-UPEC) strains, alternatives to antibiotics like phage therapy have been sought. The present study was planned to characterize and test the activity of a phage (RDN37) which was isolated from community sewage water of Chandigarh and was found to be active against MDR-UPEC.

We studied the morphology of the phage by transmission electron microscopy and determined one-step growth curve analysis and stability of the phage at various temperature and pH ranges. PCR amplification and Sanger sequencing were performed to confirm the phage family. Genome sequences from 12 related phages (BLASTn identity >95%) were obtained from the NCBI database in GenBank format. A phylogenetic analysis was conducted using the neighbour-joining method in ClustalX2 and MEGAX. Host range and lytic activity were tested by spot assay and time-kill experiment, respectively.

Phage RDN37 had a large burst size and belonged to the Myoviridae family as per transmission electron microscopy and Sanger sequencing results. It was stable over wide range of temperature (-20°,4°, 25°, 37 °C) and pH (6,7,8). The phylogenetic analysis of amplified PCR product (major coat protein gp23) grouped the phage RDN37 with Escherichia phage vB_EcoM_IME537 (MT179807) isolated from community sewage water in China. RDN37 phage was active against MDR-UPEC strains resistant to third generation cephalosporins, aminoglycosides, carbapenems, fluoroquinolones and cotrimoxazole. The multiplicity of infection (MOI) of 0.01 was found to be optimum to reduce the bacterial cell density in the time-kill assay.

RDN37 is a stable lytic phage with large burst size, specific to E. coli, has a therapeutic potential to treat UTI caused by highly drug resistant UPEC. A cocktail of multiple phages will be required to overcome its narrow host range.