The absence of reduces the invasion of but is not essential for virulence.

The contagious respiratory pathogen, , contributes to infectious coryza in poultry. However, commercial vaccines have not shown perfect protection against infectious coryza. To search for an alternative approach, this research aimed to investigate whether the quorum-sensing system of pathogens plays a crucial role in their survival and pathogenicity. The LuxS/AI-2 quorum-sensing system in many Gram-negative and Gram-positive bacteria senses environmental changes to regulate physiological traits and virulent properties, and the role of the gene in remains unclear. To investigate the effect of the gene in the quorum-sensing system of , we constructed a mutant. Bioluminescence analysis indicated that the gene plays a vital role in the LuxS/AI-2 quorum-sensing system. The analysis of the LuxS/AI-2 system-related genes showed the level of mRNA to be significantly increased in the mutant strain; however, , , and mRNA levels were not significantly different compared with the wild type. The ability of the mutant strain to invade HD11 and DF-1 cells was significantly decreased compared with the wild-type strain. In addition, all chickens challenged with various doses of the mutant strain developed infections and symptoms, and those challenged with the lowest dose exhibited only minor differences compared to chickens challenged with the wild-type strain. Thus, the deletion of the gene reduces the invasion, but the gene does not play an essential role in the pathogenesis of .