Screening Of Lactic Acid Bacteria Against Escherichia Coli K88 Infection Based On Caenorhabditis Elegans And Its Mechanism Of Action

Enterotoxingenic Escherichia E.coli(ETEC)is a pathogen that causes diarrheal diseases,mainly affecting infants and weaned piglets,and has a huge impact on public production and life.In this study,Caenorhabditis elegans(C.elegans)model was combined with in vitro screening to screen for Pediococcus acidilactici P25 with anti-ETEC K88 properties from feed ingredients,and the mechanism of P25 against ETEC K88 infection was studied.The main results of the paper are as follows:(1)Three strains of Lactic acid bacteria(LAB)C20,P16 and P25 with excellent performance were screened out from feed ingredients,and they were identified as Enterococcus hirae Pediococcus pentosaceus and Pediococcus acidilactici by physiological,biochemical and molecular biological methods.These three LABs have strong acid,acid and bile salt resistance,and P16 and P25 have strong antibacterial activity against ETEC K88.Their antibacterial ability may be related to the production of antibiotics,organic acids.(2)Based on C.elegans,the ETEC K88 challenge model was established,and based on this,a LAB screening model against ETEC K88 infection was established.The results showed that P25 is best to anti-ETEC K88 infection with C.elegans,it prolonged the semi-lethal time(DT50)of infected C.elegans to 11.36 days,and the survival rate increased to 35.94 % on the 12 th day of challenging.(3)Based on the C.elegans model,the infection mechanism of P25 against ETEC K88 was evaluated.The results showed that P25 could inhibit the colonization of ETEC K88 in the intestinal tract of C.elegans.Moreover,under in vitro co-culture conditions,P25 inhibited the growth of ETEC K88,and significantly(P < 0.05)down-regulated the ETEC K88 enterotoxin gene estB,elt expression in C.elegans in vitro and vivo.(4)The mechanism of P25 protection to C.elegans against ETEC K88 infection was analyzed by transcriptome sequencing technology.GO analysis showed that P25 may promote the expression of innate immune function-related genes in C.elegans biological processes.Pathway results indicate that P25 may play an important role in the up-regulation of the MAPK and other pathway genes of C.elegans,thereby protecting C.elegans against ETEC K88 infection.RT-qPCR verification of the expression levels of 8 genes in the MAPK signaling pathway confirmed this conclusion.