Sophorolipids Are a Potential Antimicrobial Agent in Vitro and in Broilers

Recently, the ban of antibiotic growth promoters (AGP) using in animal feeds has been rapidly spread worldwide and the needs for alternative strategies to AGP have increased. Sophorolipids (SPL) are glycolipid biosurfactants produced by non-pathogenic yeast species such as Candida bombicola. Previous researches demonstrated SPL has a selective antimicrobial activity toward Gram-positive bacteria. Therefore, two experiments were designed to investigate the possibility of SPL as an alternative to AGP in broilers. An in vitro study was conducted to estimate antimicrobial activities with various concentrations of SPL against both of Gram-positive and Gram-negative bacteria. SPL treatment showed antimicrobial activities against Streptococcus bovis, Stapylococcus aureus, Bacillus cereus, E. coli K88 and Pseudomonas aeruginosa. To confirm the result of the in vitro study, an in vivo experiment was conducted to investigate the effects of supplemental SPL as an antimicrobial agent in comparison with zinc bacitracin (ZB) in broilers. A total of 540 0-day-old Ross® 308 broilers were randomly allotted to 9 dietary treatments with 6 replicates and fed the experimental diet for 5 weeks. Dietary treatments consisted of control (CON; basal diet), ZB groups (0.025%, 0.05%, 0.10% and 0.20%) and SPL groups (0.025%, 0.05%, 0.10% and 0.20%). At the end of experiment, one bird per pen was sacrificed to collect cecal contents and gut microbiota of the samples were identified by 16S rRNA gene-pyrosequencing. A taxonomy-based analysis of cecal samples revealed that both of ZB groups and SPL groups decreased the microbial diversity and abundance compared with CON. At phylum level, two phyla, Firmicutes and Bacterodetes, were predominant (over 95%) in broiler ceca of all treatments. The ratio of Firmicutes to Bacterodetes in the cecal microbiota was greater in ZB groups than SPL groups and CON. At genus level, Barnesilella was the most abundant microbiome in CON (25.0% of total cecal microbiota). Barnesilella was decreased in ZB groups in a dose dependent manner, as an example, decreased from 25.0% in CON to 2.75% in 0.2% ZB treatment. In contrast, Barnesilella were not changed in SPL groups compared with CON. In SPL groups, supplemental SPL tended to decrease Gram-positive bacteria including Romboutsia, Lactonifactor, Turicibacter and Sporobacter. These findings indicate SPL inhibits mainly Gram-positive bacteria on both of in vitro and in vivo. Therefore, SPL and ZB induced less diversity and less abundance of cecal microbiota in broilers but SPL showed more specific and balanced antimicrobial effects than ZB.