Isolation, Characterization And In Vitro Antibacterial Activity Evaluation Of ETEC K88 Phage PE-1

Enterotoxigenic Escherichia coli(ETEC)is a common intestinal pathogen.The surface of this pathogen carries a virulence factor called adhesin.When the bacteria enter the digestive tract of the infected target.The bacteria adhere to the surface of the intestinal epithelial cells of the target by the action of adhesin,and then secrete one or more enterotoxins to stimulate the loss of water and ions in the intestinal cells,thereby causing infectious diarrhea and infecting the body quickly.Dehydration,even death.It is usually classified according to the adhesin carried by ETEC,of which ETEC K88 is most prevalent.Piglet infectious diarrhea disease caused by this kind of pathogen has strong contagiousness and high mortality,which has caused serious damage to the global pig industry.The cost of vaccination and environmental sanitation commonly used to prevent this disease is relatively high,and the problem of resistant bacteria caused by antibiotics used to treat this disease is also controversial.Therefore,it is extremely urgent to find new and effective alternative treatments.Phage is a type of virus that infects specific bacterial cells.They are widely distributed and have a strong specific killing effect on target cells.According to the different activities of phage invading cells,they are usually divided into two types: Lytic phage and Lysogenic phage.The former uses the nutrients and metabolic systems in the host after infecting the cells.Complete the amplification and release of the progeny phage and simultaneously lyse the host bacteria.The latter integrates its own genome into the host’s chromosome after invading the host matrix,and undergoes division and passage along with the host’s life cycle.Partially lysogenic phage may even cause changes in the apparent traits of the host bacteria.Accordingly,the isolation of a lytic phage having a specific killing effect on ETEC K88 can be regarded as a new solution to the problem of this bacterial infection.A potential ETEC K88 lytic phage was isolated and screened from the native environment of ETEC K88 and named it phage PE-1 in this study.The indicators of PE-1 were fully characterized and the evaluation of antibacterial effects in vitro was completed.Phage PE-1 has clear plaque edges and translucent centers,which are typical features of lytic phage.Its microstructure is similar to that of a tadpole,with a total length of about 96-100 nm.Its genomic type is a double-stranded DNA molecule.It is speculated that it belongs to the Caudovirales order,Podoviridae family.The results of biological characteristics showed that the optimal multiplicity of infection of phage PE-1 was 10 PFU/CFU,and the optimal infection stage was early logarithm of host bacteria(about 2 h).The phage PE-1 has the characteristics of short lysis cycle,short latency,rapid bursting speed and simple culture conditions.Moreover,phage PE-1 is highly tolerant,and it can maintain high activity in the range of room temperature to 65 ° C,p H of 4-11,and Na Cl concentration of not more than 4%.These above characteristics allow PE-1 to completely cover all the active conditions of the host bacteria.In the evaluation of antibacterial effect in vitro,phage PE-1 can effectively inhibit host proliferation under 1% inoculation conditions,delay the lag phase of host bacteria by more than 2 h,and reduce its concentration by 1-2 orders of magnitude.PE-1 can also effectively reduce the concentration of host bacteria that grow to a stable phase.After incubation for 4 h at a multiplicity of infection of 1 PFU/CFU,the host strain was reduced by 1.2 lg CFU/m L,which was better than the 50 μg/m L penicillin treatment group.After incubation for 4 h at a multiplicity of infection of 10 PFU/CFU,the host strain was reduced by 2.9 lg CFU/m L,and followed by the 50 μg/m L norfloxacin treatment group.In summary,phage PE-1 is a lytic phage that can rapidly control the proliferation of host bacteria.It has an in vitro antibacterial potency similar to antibiotics.The phage was also hostspecific and dependent.After the sterilization is completed,a certain titer can be maintained,and the antibacterial time can be prolonged without damaging the body.It is not easy to cause drug contamination.Therefore,it has certain development potential.