Susceptibility of Streptococcus suis to liamocins from Aureobasidium pullulans

Authors: BISCHOFF, KENNETH - Former ARS Employee; Brockmeier, Susan; Skory, Christopher - Chris; Leathers, Timothy; Price, Neil; MANITCHOTPISIT, PENNAPA - Former ARS Employee; Rich, Joseph

Submitted to: Biocatalysis and Agricultural Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2018
Publication Date: 7/2/2018
Citation: Bischoff, K.M., Brockmeier, S.L., Skory, C.D., Leathers, T.D., Price, N.P.J., Manitchotpisit, P., Rich, J.O. 2018. Susceptibility of Streptococcus suis to liamocins from Aureobasidium pullulans. Biocatalysis and Agricultural Biotechnology. 15:291-294. doi: 10.1016/j.bcab.2018.06.025.
DOI: https://doi.org/10.1016/j.bcab.2018.06.025

Interpretive Summary: Streptococcus suis (S. suis) is a major pathogen of swine that is also considered an emerging zoonotic pathogen of humans. “Liamocins” are unique antimicrobials produced by the fungus Aureobasidium pullulans that recently have been found to have antibacterial activity with specificity for Streptococcus species. However, liamocins have not previously been tested for inhibition of S. suis. In this study, strains of S. suis isolated from domestic pigs were shown to be susceptible to liamocins. In this research, statistical methods were used to optimize growth medium for liamocin production. Liamocin yields from optimized medium were nearly double those from standard medium. This work will facilitate the development of liamocins as new antimicrobial agents.

Technical Abstract: Streptococcus suis is a major pathogen of swine that is also considered an emerging zoonotic pathogen of humans. Because of increasing antibiotic resistance in S. suis, new antimicrobial agents are being sought. Liamocins are unique polyol lipids produced by certain strains of the fungus Aureobasidium pullulans. Liamocins recently have been found to have antibacterial activity with specificity for Streptococcus species. However, liamocins have not previously been tested for inhibition of S. suis. Ten strains of S. suis isolated from domestic pigs were tested for susceptibility to liamocins by the broth microdilution method. All 10 were susceptible, with MICs ranging from 39 to 78 µg/mL. Viability assays using the LIVE/DEAD BacLight Bacterial Viability Kit indicated that liamocins are bactericidal to S. suis. Cell-leakage assays showed that cells treated with liamocins leaked small molecular mass nucleic acids into the extracellular matrix, suggesting that liamocins act via disruption of the cell membrane. Liamocins thus show potential for development as a specific antibacterial to reduce colonization of S. suis in swine.