Functional characterization of a novel lytic phage EcSw isolated from Sus scrofa domesticus and its potential for phage therapy

• Active lytic phage EcSw was isolated from feces samples of pigs.
• Host Escherichia coli Sw1 was found multi antibiotic resistant.
• EcSw belongs to the family Myoviridae with approximately 70 Kbp DNA genome.
• The isolated phage was able to tolerate a wider range of environmental conditions.
• Combination therapy with antibiotics shows robust bactericidal effects to that of phage or antibiotics alone.

In this study, multi-drug resistant Escherichia coli Sw1 (E. coli Sw1) and active lytic phage EcSw was isolated from feces samples of Sus scrofa domesticus (piglet) suffering from diarrhea. Transmission electron microscopy (TEM) indicated that isolated EcSw belongs to the Myoviridae family with an icosahedral head (80 ± 4) and a long tail (180 ± 5 nm). The EcSw phage genome size was estimated to be approximately 75 Kb of double-stranded DNA (dsDNA). Phage dynamic studies show that the latent period and burst size of EcSw were approximately 20 min and 28 PFU per cell, respectively. Interestingly, the EcSw phage can tolerate a wide range of environmental conditions, such as temperature, pH and ions (Ca2+ and Mg2+). Furthermore, genome sequence analysis revealed that the lytic genes of the EcSw phage are notably similar to those of enterobacteria phages. In addition, phage-antibiotic synergy has notable effects compared with the effects of phages or antibiotics alone. Inhibition of E. coli Sw1 and 0157:H7 strains showed that the limitations of host specificity and infectivity of EcSw. Even though, it has considerable potential for phage therapy for handling the problem of the emergence of multidrug resistant pathogens.