Antibacterial activity of durian fruit-hull polysaccharide gel against bacterial isolates from bovine mastitis

Abstract

Antibacterial property of polysaccharide gel (PG) from fruit-hulls of durian (Durio zibethinus Murr.) was investigated to find a novel antibacterial agent against bacterial isolates from cow mastitis. Since the use of natural antibacterial from plant is expected to replace limited uses and contaminated residues of antibiotic un dairy. In vitro antibacterial activity of PG was performed to evaluate the susceptibility of bacterial isolates from cow mastitis. PG showed inhibitory activity against five strains of bacteria, 42 isolates of Staphylococcus spp., 34 isolates of Streptococcus spp., 13 isolates of E. coli, 5 isolates of K. pneumoniae and 15 isolates of Pseudomonas spp. In vitro susceptibility test was determined by agar diffusion method, inhibition zone of sharp and clear margin was observed on agar media with various strength of inhibitory activity by the following sequence of PG concentrations, 5> 251 2526 625> 0.32% by weight Staphylococcus spp. and Streptococcus spp were the most susceptible bacteria, while E. coli was less susceptible to PG. PG at high concentrations inhibited growth of most of tested bacteria. Broth microdilution method was used to determine a quantitative antibacterial activity of PG. Values represented MICs and MBCs of PG against bacterial isolates were demonstrated in comparison with gentamicin, All strains of bacterial isolates showed similar susceptibility to PG. The range of MBCs of PG against most of the bacterial isolates was 12.5 25 mg / ml MBC values of PG were mostly 2 times higher concentration than its MIC values. The al clearly demonstrated that most of the isolates of S. aureus went doce suscepable to PG than laboratory tested strains of S. aureus ATCC 25923. In addition, the strains of Streptococcus spp., Pseudomonas spp. and K. pneumoniae that showed ability to survive compared with gentamicin resisted strains (MBC 28 ug / ml) were found susceptible to PG with the MIC values at 12.5-25 mg / ml In comparison of the bactericidal activity of PG of Montong (M), Chanee (C) Native cultivar (Ncv) against bacteria between S. aureus and E. coli. PG of Chanee and Native cultivar showed higher bactericidal activity than PG of Monthong. Time-kill study demonstrated that the killing effect of PG against tested bacteria was obtained at PG concentration of 50, 6.25, 50, 12.5, 50 and 12.5 mg / ml in MHB medium against S. aureus (SP2), S. aureus (SP 23), S. aureus ATCC 25923. E coli (CM 49), E. coli (CM 85) and E. coli ATCC 25922, which the colony counts were declined to 0% at 8, 2, 24, 12, 16 and 24 hr, respectively. S. aureus was more susceptible to PG than E. coli, the MIC at 0.312% PG against S. aureus (SP 23) produced to colony count in 16 t, while the colony count against E. coli at the same 20 concentration was found 47,46% inhibition. The isolated bacteria was more susceptibie to PG tnan Standard bacteria. The effect of temperature on inhibitory activity of PG against S. aureus and E. coli was determine, temperatures (25 ° C and 37 ° C) were not effect killing activity of PG against S. aureus, whereas temperature at 25 ° C showed less killing activity than at 37 ° C against E. col. The effect of difference pH or bactericidal activity of PG against S. aureus and E. coli showed that PG at pH 2 and control (HCI in MHB) gave the same inhibitory effect. PG at pH 3-5 showed more inhibitory effect than control HCI in MHB), the result indicated that inhibitory effect of PG was not only due to its acidic property. The effect ionic strength at 25 and 100 mM NaCl on antibacterial activity of PG was investigated, NaCl reduced killing activity of PG against E. coli but no effect against S. aureus. The effect of divalent cations on bactericidal activity of PG demonstrated that divalent cations, BaCl₂, CaCl₂, MgCh₂ and ZnCl₂, decreased the bactericidal effect of PG against E. coli but no effect against S. aureus. ZnCl₂ in PG produced better bactericidal activity. The result in the present studies indicated that PG has potential benefit for application as an antibacterial agent against mastitis in dairy farm.