Antimicrobial property of polysaccharide gel from durian fruit-hulls

Abstract

Antimicrobial property of polysaccharide gel (PG) from fruit-hulls of durian (Durio zibethinus L.) was investigated to find a novel antimicrobial polysaccharide. Since PG was polysaccharide composed of sugars including arabinose, rhamnose, fructose, glucose and galacturonic acid. In vitro activity was performed to evaluate the susceptibility of microorganisms to PG. All standard strains of test microorganisms were susceptible to test antibiotic. PG showed inhibitory activity against 7 strains of bacteria. The susceptibility test was determined by agar diffusion method, inhibition zone of sharp and clear margin was observed on agar media with PG at concentration down to 0.32% against Bacillus subtilis ATCC 6633, Micrococcus luteus ATCC 9341, Staphylococcus epidermidis ATCC 12228, Lactobacillus pentosus ATCC 8041 and Escherichia coli ATCC 25922, to 0.625% and 1.25% against Staphylococcus aureus ATCC 6538P and Proteus vulgaris ATCC 13315, respectively. Broth macrodilution method was used to determine a quantitative antimicrobial activity of PG. Minimal Inhibitory Concentration (MIC) of PG against B. subtilis, M. luteus, S. epidermidis, E. coli and P. vulgaris was 6.4 mg/ml and against S. aureus and L. pentosus were 12.8 and 25.6 mg/ml, respectively. Time-kill study demonstrated killing effect of PG against susceptible bacteria, the results showed that colony counts of bacteria were declined to zero with 25.6 mg/ml of PG at 12 hours against B. subtilis; at 16 hours against M. luteus, E. coli and P. vulgaris; at 20 hours against S. aureus and S. epidermidis. Whereas the colony count of L. pentosus was declined to zero with 51.2 mg/ml of PG at 8 hours. Preparation of PG as polysaccharide film was also qualitative assay for antimicrobial activity. Inhibitory effect of PG film against susceptible bacteria was demonstrated a transparency area on agar medium covered with PG film. Examination of bacterial cells exposed to PG in normal saline solution under scanning electron microscope appeared an alteration on cell surface of bacteria. The development of PG resistance in S. aureus and E. coli were studied by repeated exposure method in medium containing sub-inhibitory concentration of PG. The results demonstrated that S. aureus and E. coli were not inducible to obtain the PG resistance during 30 days. Inhibitory activity of PG was not found against 4 test bacteria, Lactobacillus plantarum ATCC 14917, Salmonella typhimurium ATCC 14028, Klebsiella pneumoniae ATCC 10031 and Pseudomonas aeruginosa ATCC 9721, and 2 test yeast, Saccharomyces cerevisiae ATCC 9763 and Candida albicans ATCC 10230 in this study.