Abstract
After the introduction of a ban on the use of antibiotic growth promoters (AGPs) for livestock, the feeding environment, including the composition of animal intestinal microbiota, has changed rapidly. We hypothesized that the microbial genomes have also been affected by this legal prohibition, and investigated an important member of the swine gut microbiota, Lactobacillus salivarius, with a pan-genomic approach. Here, we isolated 21 L. salivarius strains composed of 6 strains isolated before the AGP prohibition (SBPs) and 15 strains isolated after the AGP prohibition (SAPs) at an interval of a decade, and the draft genomes were generated de novo. Several genomic differences between SBPs and SAPs were identified, although the number and function of antibiotic resistance genes were not different. SBPs showed larger genome size and a higher number of orthologs, as well as lower genetic diversity, than SAPs. SBPs had genes associated with the utilization of L-rhamnose and D-tagatose for energy production. Because these sugars are also used in exopolysaccharide (EPS) synthesis, we tried to identify differences in biofilm formation-associated genes. The genes for the production of EPSs and extracellular proteins were different in terms of amino acid sequences. Indeed, SAPs formed dense biofilm and survived better than SBPs in the swine intestinal environment. These results suggest that SAPs have evolved and adapted to protect themselves from new selection pressure of the swine intestinal microenvironment by forming dense biofilms, adopting a distinct antibiotic resistance strategy. This finding is particularly important to understand the evolutionary changes in host-microbe interaction and provide detailed insight for the development of effective probiotics for livestock.
Highlights
Antibiotic growth promoters (AGPs) have been added to livestock diets since the 1950s [1]
We isolated the L. salivarius strains that inhabited the intestinal tracts of swine from several farms of Republic of Korea under two different conditions: 1) AGPs had been used as feed additives for livestock, and 2) after the ban on AGP addition to the feeds
21 L. salivarius strains including six strains isolated before AGP prohibition (SBPs) and fifteen strains isolated after AGP prohibition (SAPs) were randomly selected
Summary
Antibiotic growth promoters (AGPs) have been added to livestock diets since the 1950s [1]. They have provided increased productivity to farmers, and the agricultural industries and the consumers have benefited from them. In the last few decades, scientists and politicians have expressed concerns about the use of antibiotics in animal feed. These include the potential development and transfer of antibiotic resistance of bacteria, which could become resilient to medicines used to treat humans, leading to increased illnesses and mortality in humans [2]. An action supporting the ban of AGPs from livestock feed was started in Europe. Republic of Korea adopted this legislation, and the regulations came into force on July 2011 [4]
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