Exploiting phages–bacteria co-evolution to overcome phage resistance and to ease the selection of new phage particles

Antibiotic resistance is one of the major threats of modern medicine. The limited conventional treatment options against multi-drug resistant bacteria, as well as the paucity of new effective antibiotics, is leading to the need of developing novel strategies, such as the therapeutic use of bacteriophages. However, it is necessary to combine a variety of phages to avoid the therapeutic inefficacy due to the possible resistance emergence to single particles. Here, we describe a novel bacteriophage, named GP-7, which was isolated from hospital wastewaters collected in Tuscany following standard methods. GP-7 was obtained using the K. pneumoniae BO-FR-1 strain, a member of sequence type 258 resistant to the infection of the previously characterized phage phiBO1E. Host spectrum was determined by spot-test and efficiency of plating techniques. Physiological features, including stability to pH and temperature changes was assessed. The kinetic of infection was defined by the one-step growth curve method. Phage genome was characterized by a next generation sequencing approach and bioinformatics analysis. GP-7 is myovirus with a strictly lytic cycle and exhibiting a narrow host spectrum restricted to its indicator strain and other K. pneumoniae phage-resistant mutants. The phage maintains its full infectivity between pH 4 and 11, and it is also stable after 1 h at 60° C. The infective cycle is characterized by a latency period of 25 min and a burst size of 45 particles. Results from this study could be of interest for the rationale design of phage cocktails to be used for therapeutic applications.