Citric Acid Promoting B Lymphocyte Differentiation and Anti-epithelial Cells Apoptosis Mediate the Protective Effects of Hermetia illucens Feed in ETEC Induced Piglets Diarrhea.

Mingming Liu,Wei Wang,Zhaoyun Xu,Yantao Lv,Bai Li,Zifan Wang,Xinxin Jin,Mingqiang Zhu,Gaijie Xie,Xue Zhang,Yanhua Huang,Haidong Xu,Boyu Yuan

doi:10.3389/fvets.2021.751861

Abstract

Newborn piglets are prone to diarrhea after weaning as a result of changes in their environment and feed. Enterotoxigenic Escherichia coli (ETEC) K88 strain is a typical pathogen that causes diarrhea in such stage of piglets. Hermetia illucens larvae are widely used in livestock and poultry production because of their high nutritional value and immunoregulatory effects. This study aimed to evaluate the protective effects of H. illucens feed in protecting against ETEC induced diarrhea in piglets and to unravel the mechanisms of immune modulation and intestinal barrier maintenance. The results showed that after ETEC infection, citric acid in the serum of the groups fed on H. illucens larvae increased significantly, which stimulated macrophages to secrete cytokines that promote B lymphocyte differentiation, ultimately increasing the production of IgA and IgG in serum. Concomitantly, citric acid also had a positive effect on the intestinal barrier damaged due to ETEC infection by inhibiting the production of inflammatory cytokines, reducing the Bcl-2/Bax ratio, and promoting the expression of tight junction proteins. Correlation analysis showed that the increase of citric acid levels might be related to Massilia. Thus, citric acid derived from H. illucens larvae can improve the immune performance of weaned piglets and reduce ETEC-induced damage to the intestinal barrier in weaned piglets.

Highlights

After the early weaning of newborn piglets, the intestinal flora is not yet well-established, and the intestinal barrier is not yet mature
The results of TUNEL staining showed that compared with the C group, Enterotoxigenic Escherichia coli (ETEC) K88mediated apoptosis was significantly inhibited in the H. illucens larvae feed groups (Figure 1D)
The changes in the ratio of Bcl-2/Bax were detected by western blotting, and the results reveal significantly increased anti-apoptotic Bcl-2/Bax ratio of the H. illucens larvae feed groups (Figure 1E)

Summary

Introduction

After the early weaning of newborn piglets, the intestinal flora is not yet well-established, and the intestinal barrier is not yet mature. Due to environmental changes, feed stress, and other risk factors, newborn piglets are often infected by pathogenic bacteria, mainly the enterotoxigenic ETEC K88, to develop diarrhea [1]. In China, the mortality rate of post-weaning diarrhea (PWD) due to ETEC K88 infection is relatively high, causing serious losses to the breeding industry [3]. Antibiotics have been widely used in the breeding industry for more than 50 years because they can effectively control bacterial diseases [4]. Following the European Union, in 2020, China banned the use of antibiotics in pig feed. Finding a new and effective antibiotic substitute for pigs has become necessary—especially for weaned piglets because of their poor immune system and weaning stress—to treat and prevent bacterial infections, including diarrhea caused by ETEC K88

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Conclusion