Susceptibility of fish-associated Flavobacterium spp. isolates to cinnamaldehyde, vanillin and Kigelia africana fruit extracts

Abstract

Phytochemicals are being explored as therapeutic alternatives in aquaculture since they have destressing, growth-promoting, appetite-increasing, immune-stimulating, and antimicrobial properties. The susceptibility of 28 Flavobacterium johnsoniae-like isolates and nine selected Flavobacterium spp. isolates to three phytochemicals, viz.: cinnamaldehyde (10-250 µg/ml), vanillin (5-500 µg/ml) and four crude Kigelia africana extracts (4-10 mg/ml ethyl acetate, dichloromethane, methanol and hexane), were assessed using disk diffusion assays and compared to standard antimicrobial agents, ampicillin and tetracycline using activity indices. Cinnamaldehyde (250 µg/ml) was more effective than 250 µg/ml vanillin, which was ineffective even at higher concentrations. K. africana extract (4 mg/ml) antibacterial efficacy decreased in the following order: Ethyl acetate, methanol, dichloromethane and hexane. The 10 mg/ml methanolic K. africana extract was most effective, with 100% of isolates displaying susceptibility, irrespective of the isolation source. Methanolic extract (10 mg/ml) activity indices ≥ 1 were obtained for 67.9 and 71.4% of isolates, respectively, relative to AMP10 and TE30. Cinnamaldehyde and the K. africana methanol extract are promising candidates to be tested for their efficacy in the treatment of Flavobacterium-associated fish infections. These phytochemicals might be environmentally-friendly, cost-effective alternatives to antimicrobial agent use in aquaculture, with a lesser potential of resistance development.

Inhibition Activity of Compounds and Bacteriophages against Flavobacterium psychrophilum Biofilms In Vitro

“…To date, certain plant extracts have been tested for their antimicrobial activity against different Flavobacterium species (Chenia and Singh ; Prasanna and Yuwvaraanni ). Similarly, the use of lytic phages has been put forward as a promising approach for the control of F. psychrophilum infections in Rainbow Trout (Madsen et al.…”