Introduction and methodology
Since their discovery, antibiotics have been used to treat bacterial infections in human and veterinary medicine. Unfortunately, their excessive and often inappropriate use has led to the development of antibiotic resistance. This means that certain antibacterial molecules may be less effective, or may no longer be effective, because bacteria have developed the ability to counteract their mechanism of action by acquiring or developing resistance genes.
Applied to the livestock sector, this means that the effectiveness of treatments for bacterial diseases may be reduced, and the associated costs of treatment and mortality may increase leading to significant economic losses. And Mediterranean aquaculture is no exception.
Currently, in addition to vaccination, research is being conducted into probiotic microorganisms and new natural compounds to help facing bacterial infections, whilst reducing the use of antibiotics. The aim of this study was to evaluate the in vitro the growth-inhibiting effectsactivity of substances as pine lipid fraction and wood polyphenols against some of the most relevant bacterial fish pathogens of Mediterranean aquaculture.This study was conducted in triplicate on 90 strains belonging to eight different bacterial species, such as Vibrio harveyi Tenacibaculum maritimum, Lactococcus garvieae, Flavobacterium psychrophilum, Photobacterium damselae subsp. piscicida, Aeromonas veronii , Aeromonas salmonicida, Yersinia ruckeri. Following the Clinical and Laboratory Standards Institute (CLSI) guidelines with some modifications, broth microdilutions in 96-well plates were performed. A 0,5 Mc Farland suspension of the microorganism under investigation was brought into contact with different concentrations (tested range: 0,0049 – 2,50%) of pine lipid fraction and wood polyphenols to determine the Minimal Inhibitory Concentration (MIC) and the Minimal Bactericidal Concentration (MBC). At the same time for each tested strain, the determination of MIC values against routinary applied antimicrobials molecules in aquaculture was also performed.
Results and discussion
Tested plant substances, in particular the pine lipid fraction, demonstrated in vitro activity against bacterial fish pathogens. Promising results in terms of MIC and MBC have been obtained, suggesting the potential beneficial role of investigated compounds if applied in aquaculture sector. In vivo assays will be necessary to confirm these preliminary results and to further support the eventual use of these environmentally friendly substances as an alternative to antibiotics in aquaculture.
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