Isolation And Characterization Of The Narrow-spectrum Salmonella Bacteriophage LSE7621 And Its Application On Foods

Salmonella is a common food-borne pathogen that can cause zoonotic diseases.Bacteriophages can specifically infect bacteria.They can be used as natural high-quality antibacterial agents and show great potential in food safety control.Compared to broad-spectrum bacteriophages,narrow-spectrum bacteriophages can reduce the risk of developing community-wide resistance and have little impact on microbial flora.In this study,Salmonella enterica serovar Enteritidis(Salmonella Enteritidis)ATCC 13076 was used as the host bacteria,and a narrow-spectrum bacteriophage was screened and isolated from sewage,named LSE7621.Basic analysis and applied research were conducted on LSE7621,and the main results were as follows:(1)Biological characteristics:LSE7621 belonged to the Caudovirales order and Myoviridae family.The optimal multiplicity of infection(MOI)of bacteriophage LSE7621 was0.1.The latent period of LSE7621 was approximately 10 min,with a burst size of approximately127 PFU/CFU.The lytic period could be roughly divided into two stages.For the first stage,the number of LSE7621 increased from(3.16±0.02)log₁₀ PFU/m L to(5.91±0.06)log₁₀PFU/m L in 30 min(10 min?40 min);for the second stage,the number of LSE7621 increased from(5.90±0.03)log₁₀ PFU/m L to(9.09±0.09)log₁₀ PFU/m L in 60 min(70 min?130 min).LSE7621 showed good p H stability(4.0?11.0)and thermal stability(30??50?).It was stable when stored at 4°C and 25?for a long time.(2)Genomics analysis:LSE7621 was a ds DNA bacteriophage,with a genome size of50936 bp and a GC content of 46.18%.The accession number of LSE7621 in Gen Bank was MK568062.There were no m RNA sequences,t RNA sequences,resistance genes and virulence factors predicted in the LSE7621 genome.LSE7621 contained 72 putative open reading frames(ORFs),and 30.5%ORFs of which encoded functional proteins,while 69.5%ORFs encoded hypothetical proteins,and no lysogenic genes were found.Evolutionary relationship analysis revealed that LSE7621 might come from an unclassified bacteriophage genus.(3)Food biocontrol effect:The lysis effect of LSE7621 on the culture suspension of Salmonella was determined,and the results showed that as the concentration of LSE7621increased,the bactericidal effect became better.In addition,the bacteria in LSE7621-treated group was less than that in the control within 6 h.When LSE7621 was administered on lettuce,the number of Salmonella was reduced by 0.86 log₁₀ CFU/m L(MOI=100)and 1.02 log₁₀CFU/m L(MOI=1)within 6 h.When LSE7621 was administered on tofu,the number of Salmonella decreased by 3.55 log₁₀ CFU/m L(MOI=100)and 1.86 log₁₀ CFU/m L(MOI=1)at4 h.When LSE7621(MOI=1 or MOI=100)was administered on minced pork,LSE7621 had no significant inhibitory effect on Salmonella at 6 h.The large and uneven surface area of meat,the complex internal tissue structure of meat and the interference of meat components might lead to the poor effectiveness of bacteriophage in controlling Salmonella.This study is the first systematic report on narrow-spectrum bacteriophages infecting Salmonella Enteritidis,which enriches the basic research of narrow-broad bacteriophages and provides new insights into the control of foodborne pathogens.