Functional evaluation of Bacillus licheniformis PF9 for its potential in controlling enterotoxigenic Escherichia coli in weaned piglets

Abstract

During the bacterial selection, isolate PF9 demonstrated tolerance to low pH and high bile salt and an ability to extend the lifespan of C. elegans infected with enterotoxigenic Escherichia coli (ETEC) (P < 0.05). Thirty-two weaned piglets susceptible to ETEC F4 were randomly allocated to 4 treatments as follows: 1) non-challenged negative control group (NNC; basal diet and piglets gavaged with phosphate-buffered saline (PBS)); 2) negative control group (NC; basal diet and piglets challenged with ETEC F4, 3 × 107 CFU per pig); 3) positive control (PC; basal diet + 80 mg·kg-1 of avilamycin and piglets challenged with ETEC F4); and 4) probiotic candidate (PF9; control basal diet + 2.5 × 109 CFU·kg-1 diet of B. licheniformis PF9 and piglets challenged with ETEC F4). The infection of ETEC F4 decreased average daily gain (ADG) and gain:feed in the NC group when compared to the NNC group (P < 0.05). The inoculation of ETEC F4 induced severe diarrhea at 3 h post-inoculum (hpi), 36 hpi, 40 hpi in the NC group when compared to the NNC group (P < 0.05). The supplementation of B. licheniformis PF9 significantly relieved diarrhea severity at 3 hpi when compared to the NC group (P < 0.05). The inoculation of ETEC F4 reduced duodenal, jejunal and ileal villus height (VH) in the NC group when compared to the NNC group. A significant (P < 0.05) decrease was detected in the duodenal VH in the PC and NNC groups. Moreover, the NNC group had a reduced relative mRNA level of Na+-glucose cotransporter 1 (SGLT1) when compared to the NC group (P < 0.05). Compared to the NC and NNC groups, the supplementation of B. licheniformis PF9 increased the relative mRNA levels of aminopeptidase N (APN), occludin (OCLN), zonula occludens-1 (ZO-1), and SGLT1 (P < 0.05). The supplementation of B. licheniformis PF9 also significantly increased the relative mRNA level of excitatory amino acid transporter 1 (EAAC1) when compared to the NC group (P < 0.05). Piglets supplemented with B. licheniformis PF9 showed lower relative abundance of Bacteroidetes in the colon than piglets from the NNC group (P < 0.05). The NNC group had a higher relative abundance of Firmicutes in the ileum than all the challenged piglets (P < 0.05); however, a lower relative abundance of Proteobacteria in the ileum and colon was observed in the NC group (P < 0.05). This study provides evidence that B. licheniformis PF9 has the potential to improve the gut health of piglets under challenging conditions.