Antibacterial activity of liamocins oil from Aureobasidium pullulans is specific for species of Streptococcus.

Liamocins are a heterogeneous mixture of denser-than-water oils produced by the fungus Aureobasidium pullulans.  Liamocins have unique chemical structures with a mannitol head group linked to long chain polyester tails consisting of multiple 3,5-dihydroxydecanoic acid ester groups, some of which are O-acetylated.  Broth dilution susceptibility testing determined that liamocins oil from A. pullulans NRRL 50380 possessed antibacterial activity against Streptococcus species.  MICs ranged from ≤10 μg/ml to 78 μg/ml for the following: S. agalactiae, S. infantarius, S. mitis, S. mutans, S. pneumonia, S. salivarius, S. suis, and S. uberis.  Enterococcus faecalis and Bacillus subtilis were less susceptible (MIC = 312 μg/ml and 625 μg/ml, respectively), while the following bacteria were not susceptible (MIC > 1250 μg/ml): Staphylococcus aureus, Lactobacillus fermentum, Escherichia coli, and Pseudomonas aeruginosa.  Structural analogs of liamocins were produced by growing A. pullulans on various sugar alcohols.  Liamocins containing arabitol, threitol, and xylitol headgroups possessed antibacterial activity, but MICs were higher than those for the mannitol liamocins.  The liamocin components were separated by HPLC and assayed by MALDI-TOF/MS, and a fraction that was enriched for liamocin B1 (the non-acetylated type with four 3,5-dihydroxydecanoic acid groups) had the highest antibacterial activity (MIC = 16 μg/ml).  Treatment with 39 μg/ml liamocin reduced viability of S. agalactiae from 6.7 log(CFU/ml) to 3.4 log(CFU/ml) within 1 hour, suggesting that liamocin oil is bactericidal.  Liamocins have potential application as a narrow spectrum antimicrobial agent that targets streptococcal pathogens, but avoids disruption of normal flora and reduces selection for antibiotic resistance in commensal bacteria.