bacteriophages targeting multidrug-resistant bacteria
Bacteriophage therapy is considered a promising strategy for treatment of multidrug-resistant bacteria, such as pathogenic Escherichia coli involved in urinary tract infections (UTIs), and Shigella spp., the main culprit in diarrheal illnesses in children in developing countries. Because of the propensity of both bacteria to acquire resistance to antibiotics, phages have become an increasingly feasible strategy for their treatment, but there remain many limitations to the use of phages in the treatment of  antibiotic-resistant bacteria. We identified six unique bacteriophages that have activity against a broad spectrum of clinical isolates of both E. coli and Shigella spp. and characterized their host ranges against 270 pathogenic E. coli isolates from subjects with UTIs and 26 isolates of Shigella spp. from subjects with diarrheal disease. We characterized phage lysis through a double layer plate test and growth curve kinetics and found that most of the bacterial isolates tested were susceptible to at least one of the phages. Only eight out of 297 (2.7%) could not be lysed by any of the 6 phages tested. Bacteriophage FM10 was the most effective phage, showing inhibition on the 88.5% of all the E. coli tested. Bacteriophage LF2 showed the best performance against Shigella spp. strains being able to completely lyse the 96.0% of all the isolates tested, followed by DP16. LF2 and DP16 were able to inhibit the growth in kinetics test of 4 multidrug resistant Shigella spp. isolates alone or in cocktail in 72 hours. The phages in this study also were analyzed by whole genome sequencing (WGS) and transmission electron microscope (TEM). They all belonged to the family of Straboviridae without pathogenicity or lysogenic genes found.  Since E. coli and Shigella spp. are relatively closely related, it is not surprising that we identified phages capable of lysing both of organisms, but the identification of phages with relatively broad host ranges against clinical isolates of both is promising for overcoming one of the major obstacles limiting the use of phages in the treatment of antibiotic-resistant E. coli and Shigella spp. infections.