Probiotic roles of Lactobacillus sp. in swine: insights from gut microbiota.

The use of lactobacilli as probiotics in swine has been gaining attention due to their ability to improve growth performance and carcass quality, prevent gastrointestinal infection and most importantly, their 'generally recognized as safe' status. Previous studies support the potential of lactobacilli to regulate host immune systems, enhance gut metabolic capacities and maintain balance in the gut microbiota. Research on swine gut microbiota has revealed complex gut microbial community structure and showed the importance of Lactobacillus to the host's health. However, the species- and strain-specific characteristics of lactobacilli that confer probiotic benefits are still not well understood. The diversity of probiotic traits in a complex gut ecosystem makes it challenging to infer the relationships between specific functions of Lactobacillus sp. and host health. In this review, we provide an overview of how lactobacilli play a pivotal role in the swine gut ecosystem and identify key characteristics that influence gut microbial community structure and the health of pigs. In addition, based on recent and ongoing meta-omics and omics research on the gut microbiota of pigs, we suggest a workflow combining culture-dependent and culture-independent approaches for more effective selection of probiotic lactobacilli.

In vitro evaluation of the mucin-adhesion ability and probiotic potential of Lactobacillus mucosae LM1.

AIMS: In this report, we characterized the probiotic potential of Lactobacillus mucosae LM1, focusing on its in vitro mucin-adhesion abilities. METHODS AND RESULTS: Screening assays were used to evaluate LM1. Previous studies on Lact. mucosae species have been performed, but few have examined the ability of this species to adhere to and colonize the intestinal mucosa. Thus, adhesion, aggregation and pathogen inhibition assays of LM1 along with microbial adhesion to solvents (MATS) assay were carried out in comparison with another putative probiotic, Lactobacillus johnsonii PF01, and the commercial strain, Lactobacillus rhamnosus GG. Based on MATS assay, the cell surfaces of the lactobacilli strains were found to be hydrophobic and highly electron-donating, but the average hydropathy (GRAVY) index of predicted surface-exposed proteins in the LM1 genome indicated that most were hydrophilic. LM1 showed the highest adhesion, aggregation and hydrophobicity among the strains tested and significantly inhibited the adhesion of Escherichia coli K88 and Salmonella enterica serovar Typhimurium KCCM 40253. Correlations among adhesion, aggregation and hydrophobicity, as well as between coaggregation and displacement of E. coli, were observed. CONCLUSIONS: Increased adhesion may not always correlate with increased pathogen inhibition due to various strain-specific mechanisms. Nevertheless, LM1 has promising probiotic properties that can be explored further using a genomics approach. SIGNIFICANCE AND IMPACT OF THE STUDY: Our data on adhesion of LM1 strain showed a significant correlation between adhesion, hydrophobicity of cell surface and autoaggregation. This study gives basic knowledge for the elucidation of the adhesion mechanism of Lactobacillus sp. and prediction of its adherence in specific host models.

Molecular cloning, characterization and comparison of bile salt hydrolases from Lactobacillus johnsonii PF01.

AIMS: To clone, characterize and compare the bile salt hydrolase (BSH) genes of Lactobacillus johnsonii PF01. METHODS AND RESULTS: The BSH genes were amplified by polymerase chain reaction (PCR) using specific oligonucleotide primers, and the products were inserted into the pET21b expression vector. Escherichia coli BLR (DE3) cells were transformed with pET21b vectors containing the BSH genes and induced using 0·1 mmol l(-1) isopropylthiolgalactopyranoside. The overexpressed BSH enzymes were purified using a nickel-nitrilotriacetic acid (Ni(2+) -NTA) agarose column and their activities characterized. BSH A hydrolysed tauro-conjugated bile salts optimally at pH 5·0 and 55°C, whereas BSH C hydrolysed glyco-conjugated bile salts optimally at pH 5·0 and 70°C. The enzymes had no preferential activities towards a specific cholyl moiety. CONCLUSIONS: BSH enzymes vary in their substrate specificities and characteristics to broaden its activity. Despite the lack of conservation in their putative substrate-binding sites, these remain functional through motif conservation. SIGNIFICANCE AND IMPACT OF THE STUDY: This is to our knowledge the first report of isolation of BSH enzymes from a single strain, showing hydrolase activity towards either glyco-conjugated or tauro-conjugated bile salts. Future structural homology studies and site-directed mutagenesis of sites associated with substrate specificity may elucidate specificities of BSH enzymes.