Antibiotics

Biography

Biography: Kenneth Bischoff

Abstract

Liamocins are a heterogeneous mixture of polyol-lipids produced by the fungus Aureobasidium pullulans. When grown on sucrose, A. pullulans strain NRRL 50380 produces four types of liamocins with chemical structures consisting of a single mannitol headgroup partially O-acylated with polyester tails containing three or four 3,5-dihydroxydecanoic ester groups, some of which are acetylated. Liamocins possessed antibacterial activity with specificity against Streptococcus species with MICs ranging 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, while the following bacteria were not susceptible: Staphylococcus aureus, Lactobacillus fermentum, Escherichia coli, and Pseudomonas aeruginosa. In an effort to improve yields (typically 0.5-6.0 g liamocin/L), different growth media and strains of A. pullulans were tested. Selective growth on different polyols resulted in considerable structural variation of liamocins including some with galactitol, sorbitol, D-arabitol, D-xylitol, and D- or L-threitol headgroups. Liamocins with D-arabitol or D/L-threitol headgroups were active but to a lesser extent than the mannitol liamocins. The components of mannitol liamocins 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 against S. agalactiae (MIC = 16 µg/ml). 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.