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

Abstract

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.