LAUSR

Rumen fluid contains factors that inactivate autoinducers, monitor microflora development and prevent the mobilization of virulence properties, and thus, the formation of resistant bacteria. The aim of this study was to assess the ability of rumen fluid to suppress the intercellular communication of bacteria by inactivating the N-acyl-homoserine lactones. We used strains of luminescent Escherichia coli JLD271 which were transformed with plasmids containing quorum sensing genes and luminescence genes. Bacteria were cultivated in LB agar medium containing 10 ug/ml doxycycline then in LB medium until the early exponential growth phase. The autoinducers used were N-butyryl-L-homoserine lactone (C4-HSL), N-(3oxo)-hexanoyl-L-homoserine lactone (oxo-С6-HSL) and N-dodecanoyl-L-homoserine lactone (C12-HSL). The ruminal fluid of young calves was collected via a fistula. Equal volumes of ruminal fluid and autoinducers were incubated then added to the cultures of luminescent bacterial strains. Dilution of the ruminal fluid up to 12.5% did not affect the luminescence of the bacterial biosensors. Incubation of ruminal fluid with N-acyl-homoserine lactones decreased their activity, marked by unexpressed specificity. The most effective inhibition of the N-(3-oxo)-hexanoyl-L-homoserine lactone was observed at 10-7 M, and above this concentration the efficiency of quorum sensing inhibition decreased. Ruminal fluid was able to inactivate Nacyl-homoserine lactones, and the efficiency of inhibition was not related to the length of the alkyl tail in the signal molecule. This suggests the ability of the ruminant digestive system to control bacteria by the inactivation of N-acyl-homoserine lactones, which regulate the quorum sensing system.