AUTHOR=Jiang Xiaobing , Jiang Congyi , Yu Tao , Jiang Xiaojie , Ren Siyu , Kang Rui , Qiu Shuxing 

TITLE=Benzalkonium Chloride Adaptation Increases Expression of the Agr System, Biofilm Formation, and Virulence in Listeria monocytogenes

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.856274

DOI=10.3389/fmicb.2022.856274

ISSN=1664-302X

ABSTRACT=<p>Benzalkonium chloride (BC) is widely used for disinfection in food industry. However, prolonged exposure to BC may lead to the emergence of BC adapted strains of <italic>Listeria monocytogenes</italic>, an important foodborne pathogen. Until now, two communication systems, the LuxS/AI-2 system and the Agr system, have been identified in <italic>L. monocytogenes</italic>. This study aimed to investigate the role of communication systems in BC adaptation and the effect of BC adaptation on two communication systems and the communication-controlled behaviors in <italic>L. monocytogenes</italic>. Results demonstrated that the Agr system rather than the LuxS system plays an important role in BC adaptation of <italic>L. monocytogenes</italic>. Neither <italic>luxS</italic> expression nor AI-2 production was affected by BC adaptation. On the other hand, the expression of the <italic>agr</italic> operon and the activity of the <italic>agr</italic> promoter were significantly increased after BC adaptation. BC adaptation enhanced biofilm formation of <italic>L. monocytogenes</italic>. However, swarming motility was reduced by BC adaptation. Data from qRT-PCR showed that flagella-mediated motility-related genes (<italic>flaA</italic>, <italic>motA</italic>, and <italic>motB</italic>) were downregulated in BC adapted strains. BC adaptation increased the ability of <italic>L. monocytogenes</italic> to adhere to and invade Caco-2 cells but did not affect the hemolytic activity. Compared with the wild-type strains, the expression levels of virulence genes <italic>prfA</italic>, <italic>plcA</italic>, <italic>mpl</italic>, <italic>actA</italic>, and <italic>plcB</italic> increased more than 2-fold in BC adapted strains; however, lower than 2-fold changes in the expression of hemolysis-associated gene <italic>hly</italic> were observed. Our study suggests that BC adaptation could increase the expression of the Agr system and enhance biofilm formation, invasion, and virulence of <italic>L. monocytogenes</italic>, which brings about threats to food safety and public health. Therefore, effective measures should be taken to avoid the emergence of BC adapted strains of <italic>L. monocytogenes</italic>.</p>