Under the global pressure of restricting the usage of antibiotic in food animals, the selection of antimicrobial alternatives has been an increasing interest in feed industry. Generally, bacteriostatic effects of functional additives are normally evaluated by reaching a certain minimum inhibitory concentration (MIC) in in vitro bacterial susceptibility tests, and it is considered that plant extracts having MICs of 100~1000 μg/ml possess antibacterial activities. However, sometimes MIC may hardly predict the in vivo effect. For example, result of a recent study on the efficacy of several commercial functional additives against Campylobacter in broilers has shown that only of 24 additives has persistent reducing effect on Campylobacter count during the entire rearing period. Considering a big gap can exist between bacteriostatic effect gained from in vitro and in vivo tests, new approaches should be introduced to investigate the potential effect of functional feed additive ingredients on gut microbial populations in vivo.
How we investigated or researched the problem?
Many (virulent) bacterial signalling mechansims depend on the expression of the quorum sensing (QS) process. Therefore, interference with QS can be done by phytochemicals at low concentrations, and can alter microbial composition and suppress the pathogenic bacterial function rather than killing the bacteria. Also, no selective pressure for the development of resistance against QS inhibition is expected to be very low. Based on the result of anti-QS evaluation, we selected a botanical mixture to test if it can affect the gut microbial activity and composition, and eventually the zootechnical performance of broilers.