Phage Therapy For Infections Caused By Common Drug Resistant Bacteria

The emergence of drug-resistance is highly relative to the use of antibiotics.Both methicillin-resistant Staphylococcus aureus(MRSA)and carbapenem-resistant Acinetobacter baumannii(CRAB)are typical multi-drug resistant bacteria.In recent years,the prevalence of MRSA and CRAB were high.They are difficult to treat and cause hospital and community associated diseases including skin and soft-tissue infection,lower respiratory tracts infection and bloodstream infection.It is urgent to find alternative solution for multi-drug resistant bacteria infections.Bacteriophages are viruses which can kill their host bacteria and phage therapy seem potential against multi-drug resistant bacteria infections.In this study,the two newly reported bacteriophages were isolated from sewage.The biological characterization and complete genome sequence of S.aureus phage SH-St 15644 and A.baumannii phage SH-Ab 15599 were reported.Electron microscopy analysis showed that SH-St 15644 belongs to Siphoviridae,and SH-Ab 15599 belongs to Myoviridae.Among the 37 clinical MRSA isolates tested,12(32%)were lysed by SH-St 15644,and SH-Ab 15599 could lyse 15(29.4%)of the 51 clinical CRAB isolates.Both SH-St 15644 and SH-Ab 15599 remained relatively stable under a wide range of temperatures or pH.80% of phage SH-St 15644 was approximately adsorbed to the host MRSA isolate in 4 min.The one-step growth curve of SH-St 15644 showed that the latent period was about 12 min followed by the growth period(about 9 min).The burst size was estimated at 13 PFU per infected cell.90% of phage SH-Ab 15599 was approximately adsorbed to the host CRAB isolate in 5 min.The one-step growth curve of SH-Ab 15599 showed that the latent period was about 10 min and the growth period was about 20 min.The burst size was estimated at 43 PFU per infected cell.Both SH-St 15644 and SH-Ab 15599 efficiently lysed the host bacteria in vitro.The genome of SH-St 15644 is a linear,45111 bp double-stranded DNA with GC content of 33.35%,and the genome of SH-Ab 15599 is a linear,143204 bp double-stranded DNA with GC content of 38.45%.No identified antibiotic resistance or virulence genes of the two phages were found in the genome.To further evaluate the therapeutic potential of SH-St 15644,a skin infection model was performed.The phage-treated mice showed smaller skin lesion size and lower CFU counts,as compared with the MRSA-infected mice.Histological examinations on the abscesses from phage-treated mice showed less damage of tissue structure than those from MRSA-infected group.These results showed the potential of SH-St 15644 to impede MRSA skin infection in vivo.In conclusion,the biological characterization and complete genome sequence of the two newly isolated phages were reported,and the therapeutic potential of SH-St 15644 were evaluated using a skin infection model.Both SH-St 15644 and SH-Ab 15599 seem to be alternatives against MRSA and CRAB infections in the future.