Effects of supplementation of Bacillus amyloliquefaciens on performance, systemic immunity, and intestinal microbiota of weaned pigs experimentally infected with a pathogenic enterotoxigenic E. coli F18

Abstract

The objective of this study was to investigate the effects of dietary supplementation of <i>Bacillus (B.) amyloliquefaciens</i> on growth performance, diarrhea, systemic immunity, and intestinal microbiota of weaned pigs experimentally infected with F18 enterotoxigenic <i>Escherichia coli</i> (ETEC). A total of 50 weaned pigs (7.41 ± 1.35 kg BW) were individually housed and randomly allotted to one of the following five treatments: sham control (CON-), sham <i>B. amyloliquefaciens</i> (BAM-), challenged control (CON+), challenged <i>B. amyloliquefaciens</i> (BAM+), and challenged carbadox (AGP+). The experiment lasted 28 days, with 7 days of adaptation and 21 days after the first ETEC inoculation. ETEC challenge reduced (<i>P</i> < 0.05) average daily gain (ADG) of pigs. Compared with CON+, AGP+ enhanced (<i>P</i> < 0.05) ADG, while <i>B. amyloliquefaciens</i> supplementation tended (<i>P</i> < 0.10) to increase ADG in pigs from days 0 to 21 post-inoculation (PI). The ETEC challenge increased (<i>P</i> < 0.05) white blood cell (WBC) count on days 7 and 21 PI, while BAM+ pigs tended (<i>P</i> < 0.10) to have low WBC on day 7 PI and had lower (<i>P</i> < 0.05) WBC on day 21 PI compared with CON+. In comparison to AGP+ fecal microbiota, BAM+ had a lower (<i>P</i> < 0.05) relative abundance of <i>Lachnospiraceae</i> on day 0 and <i>Clostridiaceae</i> on day 21 PI, but a higher (<i>P</i> < 0.05) relative abundance of <i>Enterobacyeriaceae</i> on day 0. In ileal digesta, the Shannon index was higher (<i>P</i> < 0.05) in BAM+ than in AGP+. Bray-Curtis PCoA displayed a difference in bacterial community composition in ileal digesta collected from sham pigs vs. ETEC-infected pigs on day 21 PI. Pigs in BAM+ had a greater (<i>P</i> < 0.05) relative abundance of Firmicutes, but a lower (<i>P</i> < 0.05) relative abundance of Actinomycetota and Bacteroidota in ileal digesta than pigs in AGP+. Ileal digesta from AGP+ had a greater (<i>P</i> < 0.05) abundance of <i>Clostridium sensu stricto</i> 1 but lower (<i>P</i> < 0.05) <i>Bifidobacterium</i> than pigs in BAM+. In conclusion, supplementation of <i>B. amyloliquefaciens</i> tended to increase ADG and had limited effects on the diarrhea of ETEC-infected pigs. However, pigs fed with <i>B. amyloliquefaciens</i> exhibit milder systemic inflammation than controls. <i>B. amyloliquefaciens</i> differently modified the intestinal microbiota of weaned pigs compared with carbadox.