Article Sharing | Interactions Between the Porcine Host and Gut Microbiota — The Role of Antibiotics

Interactions Between the Porcine Host and Gut Microbiota — The Role of Antibiotics

In commercial farms, antibiotics are frequently added to pig feed and drinking water to prevent bacterial infections or promote growth. However, although antibiotics can promote growth in piglets, their use often increases the proportion of pathogenic species that suppress normal intestinal function and negatively affect the symbiotic microbiota. In particular, antibiotics such as penicillin, tylosin, sulfamethazine, and tetracycline have been shown to influence the composition of the intestinal microbiota in growing pigs.

Furthermore, compared with other intestinal compartments and feces in pigs, the simultaneous administration of multiple antibiotics—namely chlortetracycline, sulfadiazine, and penicillin (ASP250)—can significantly increase the proportion of Escherichia coli in the ileal lumen and mucosa. Many functional changes observed in metagenomic analyses have also been attributed to the increase in E. coli. In addition, after the administration of the ASP250 antibiotic combination to weaned piglets, the number of lactic acid bacteria (LAB) and streptococci decreased, while Proteobacteria increased, particularly the E. coli population.

Another study reported that short-term use of low-dose antibiotics in feed can increase both the abundance and diversity of antibiotic resistance genes in animals that had never previously been exposed to those antibiotics.

Moreover, studies have found that treatment with amoxicillin (600 mg/kg) increases the abundance of fecal enterobacteria, while reducing the proportion of LAB in the jejunum, as well as decreasing total bacterial activity and total serum IgM concentration. In addition, research by Gao et al. demonstrated that therapeutic antibiotic use alters the composition and metabolism of microbial communities in the ileum and feces. However, the ileal microbiota was found to be more susceptible to change than the fecal microbiota.

Specifically, the abundance of Lactobacillus and Bifidobacterium decreased threefold and 508-fold in the ileum on day 2 and day 13, respectively, and decreased 45-fold and 72-fold in feces on day 7 and day 13. Meanwhile, the proportion of Escherichia–Shigella in the ileum increased 265-fold between day 2 and day 13, and increased 36-fold in feces between day 7 and day 13. This study also indicated that microbial community changes are closely associated with alterations in the production of specific microbial metabolites, such as short-chain fatty acids (SCFAs), which can serve as biomarkers for determining gut microbiota stability.

The total SCFA content extracted from feces—including acetate, propionate, butyrate, and valerate—is considered an effective indicator of intestinal health. In a recent study, pigs fed a conventional diet (including three types of antibiotics) were found to harbor more than 87 antibiotic resistance genes in the gastrointestinal tract compared with pigs fed an organic diet, although no significant differences were observed in the intestinal microbiota between the two groups. Among the unique gene families identified in the pig fecal genome, antibiotic resistance virulence factors were detected, showing the highest sequence homology with genes from Bacteroides, Clostridium, and Methanosphaera.

Due to the excessive use of antibiotics in pig production, animals have been found to develop tolerance to multiple pathogenic microbial species at an early stage of life. Furthermore, it has been demonstrated that antibiotics can suppress systemic immune responses in mice. As a result, tolerance formed early in life when encountering similar pathogens may lead to inefficient immune responses later in life.