Isolaiton, Characetirzation And Biological Features Of Lytic Bacteirophages Infecitng Acinetobacterbaumannii Clinical Isolaets

Acinetobacter baumannii, widely distributing in soil, water and hospitalenvironment, is a non-fermentative, gram-negative, non-motile, oxidase-negativebacillus, and belongs to the genus Acinetobacter which includes A baumannii, Acalcocacetous, A junii, A lwoffi, A haemolyticus and A johnsonii. Extensive usage ofbroad-spectrum antibiotics has led to increasing emergence of drug-resistantpathogens or opportunistic pathogens (such as Acinetobacter baumannii), particularlymulti-drug resistant organisms, for example,"superbugs". This has caused greatattention. Bacterial resistance has become the focus of global attention in medicalfield, especially the "superbugs" appeared frequently, humanity is re-entering thepre-antibiotic era. Phages are viruses specifically infecting bacteria, and theirspecificity and efficiency rekindled the interest in phage therapy against bacterialinfection. Therefore, research institutions worldwide began to explore the feasibilityof using phage to deal with bacterial infections (particularly infections caused bydrug-resistant strains).In our study,3lytic bacteriophages, ФAb-1, ФAb-2and ФAb-3, were isolatedand identified from swage using Acinetobacter baumannii clinical isolates. Thebiological characteristics of these toxic phages are as following:(1) Transmissionelectron microscopy revealed that all the phage particles had icosahedra heads, with50nm in diameter, and short non-contractile tail, assigning them to the orderCuadovirales, the family Podoviridae;(2) Restriction digestion of bacteriophageФAb-1DNA showed that the size of phage DNA was found to be40kb,approximately, the genome of bacteriophage ФAb-1have different restriction sites ofHind III、EcoR V、Nde I、BamH I and Afl III, nucleic acid of phage was circular,double-stranded DNA molecule;(3) Structural protein analysis by SDS-PAGE demonstrated bacteriophage ФAb-1harbored eight to nine proteins ranging from29～116kDa;(4) Multiplicity of infection (MOI) of bacteriophage ФAb-1was10-2;(5)One-step growth experiment illustrated that bacteriophage ФAb-1had a latent periodof20min and a burst period of30min, the burst size of bacteriophage ФAb-1was190PFU/cell;(6) Host-range specificity test showed only three strains ofAcinetobacter baumannii isolates lysed by bacteriophage ФAb-1;(7) Phage titer didnot change significantly in storage at-70℃and4℃,On the basis of isolation and identification of lytic phages infectingAcinetobacter baumannii isolates, a murine model of gut-derived sepsis was inducedby administering cyclosphosphamide and ampicillin while feeding Acinetobacterbaumannii to BALB/c mice. We evaluated the efficacy of phage therapy againstmurine gut-derived sepsis caused by Acinetobacter baumannii. The results indicatedthat phage therapy significantly increased the survival rate compared to that of controlmice treated with saline. In conclusion, our data suggest that oral administration ofphage may be effective against gut-derived sepsis caused by Acinetobacter baumannii.We look forward to further studies and to the possible use of phage treatment as aclinical therapy for humans.