Nanosilver-marine fungal chitosan as antibiotic synergizers against sepsis fish bacteria

BACKGROUND AND OBJECTIVES: Mortality is highly variable within population of cultured fish due to virulent bacteria causing fish septicemia. The use of nano-silver marine fungal chitosan as antibiotic synergisers could be an alternative in the treatment of sepsis fish pathogens. MATERIALS AND METHODS: Different bulk chitosan solutions were prepared from the mycelia of four marine fungi (Aspergillus terreus, Aspergillus flavipes, Tricoderma hamatum and Fennellia flavipes) and used as capping agents for silver nanoparticles. In vitro, the antibacterial activity of these preparations was determined against nine fish-sepsis causing bacteria, alone and in combination with nine antibiotics of choice used in aquaculture. Prepared fungal chitosans (Cs(F)) were characterized by yield of chistosan obtained, degree of deacetylation and viscosity. RESULTS AND CONCLUSION: The maximum yield of chitosan (28%) was obtained from Aspergillus terreus. A. terreus chitosan (Cs(F)), silver nanoparticles (AgNPs) and chitosan-silver nanoparticles (Cs(F)-AgNPs) showed maximum activity at the minimum inhibitory concentrations average (MIC(AVG)) 27.2, 18.2 and 7.9 μg/ml, respectively. Combination of Cs(F) -AgNPs with amikacin (Ak) and rifampicin (RD) reduced the MIC values by 96 and 94%, respectively, with fractional inhibitory concentration index (FICI) = 0.42 and 0.50 as synergistic effect. It is promising to use Cs(F)-AgNPs as enhancing agent in combination with antibiotics for fish sepsis therapy.