Indigenous AHL‐degrading bacteriumBacillus firmussw40 affects virulence of pathogenicAeromonas hydrophilaand disease resistance of gibel carp

Abstract

Interrupting quorum sensing represents a novel anti-infective strategy to combat bacterial pathogen, and biodegradation of quorum sensing signal AHLs has been proved to be an efficient way to control pathogenic Gram-negative bacteria in aquaculture.In this study, the effect of Bacillus firmus sw40 as efficient AHL-degrading strain on virulence of fish pathogen Aeromonas hydrophila and disease resistance of gibel carp Carassius auratus gibelio was investigated. The results demonstrated that in vitro the B. firmus sw40 extracellular production (ECP) was able to significantly decrease protease production, haemolytic activity and biofilm formation in A. hydrophila. Dietary administration of B. firmus sw40 (10 9 CFU/g) for 4 weeks significantly reduced the inflammatory cytokines TNF-1a, TNF-2a and IFN-γ genes expression, antioxidant parameter MDA and GSH levels in serum and increased antioxidant enzyme SOD activity. Besides, B. firmus sw40 could significantly increase the survival of gibel carp with pathogenic A. hydrophila infection. K E Y W O R D S Aeromonas hydrophila, AHL, antibiotic alternative, Bacillus firmus, quorum quenching How to cite this article: Li M-Y, Xi B-W, Qin T, Chen K, Ren M-C, Xie J. Indigenous AHL-degrading bacterium Bacillus firmus sw40 affects virulence of pathogenic Aeromonas hydrophila and disease resistance of gibel carp. Aquac Res.

Effects of glycyrrhetinic acid β on growth and virulence of Aeromonas hydrophila

“…Azocasein assay was used to detect protease activity as previously reported (Li et al, 2019). Briefly, the filtrate (150 μl) and 0.3% azocasein (1 ml, dissolved in Tris-HCl, pH 7.5) were incubated at 37°C for 30 min, and the reaction was terminated with 500 μl 10% trichloroacetic acid.…”

“…The hemolytic activity was determined as described previously (Li et al, 2019). Briefly, 100 μl filtrate, 100 μl 4% sheep blood cells and 800 μl sterile saline was incubated at 37°C for 30 min.…”