Biofilm-isolated Listeria monocytogenes exhibits reduced systemic dissemination at the early (12–24 h) stage of infection in a mouse model

Authors: BAI, XINGJIAN - Purdue University; LIU, DONGQI - Purdue University; XU, LUPING - Purdue University; TENGURIA, SHIVENDRA - Purdue University; DROLIA, RISHA - Purdue University; GALLINA, NICHOLAS - Purdue University; COX, ABIGAIL - Purdue University; KOO, OK-KYUNG - Gyeongsang National University; BHUNIA, ARUN - Purdue University

Submitted to: npj Biofilms and Microbiomes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2021
Publication Date: 2/8/2021
Citation: Bai, X., Liu, D., Xu, L., Tenguria, S., Drolia, R., Gallina, N.L., Cox, A.D., Koo, O., Bhunia, A.K. 2021. Biofilm-isolated Listeria monocytogenes exhibits reduced systemic dissemination at the early (12–24 h) stage of infection. npj Biofilms and Microbiomes. Available online:npj Biofilms and Microbiomes (2021) 7:18. https://doi.org/10.1038/s41522-021-00189-5.
DOI: https://doi.org/10.1038/s41522-021-00189-5

Interpretive Summary: In food production facilities, biofilms (bacteria attached to surfaces) are a major source for food contamination by pathogens; however, the pathogenesis of bacteria isolated from biofilms is not well understood. We investigated the pathogenesis of immobilized Listeria monocytogenes (Lm) using cell culture and mouse models. Results from the study demonstrate that the virulence of biofilm-isolated Lm is temporarily attenuated but can be upregulated in mice during the early stage (12–24 hours post-infection; hpi) and fully restored at a later stage (48 hpi) of infection. Our study further demonstrates that the cell culture assay is unreliable and, therefore, an animal model is essential for studying the pathogenesis of biofilm-isolated bacteria. Application of these results will improve the quality of future studies designed to enhance our understanding of the role of biofilms in bacterial pathogenesis.

Technical Abstract: Environmental cues promote microbial biofilm formation and physiological and genetic heterogeneity. In food production facilities, biofilms produced by pathogens are a major source for food contamination; however, the pathogenesis of biofilm-isolated sessile cells is not well understood. We investigated the pathogenesis of sessile Listeria monocytogenes (Lm) using cell culture and mouse models. Lm sessile cells express reduced levels of the lap, inlA, hly, prfA, and sigB and show reduced adhesion, invasion, translocation, and cytotoxicity in the cell culture model than the planktonic cells. Oral challenge of C57BL/6 mice with food, clinical, or murinized-InlA (InlAm) strains reveals that at 12 and 24 h post-infection (hpi), Lm burdens are lower in tissues of mice infected with sessile cells than those infected with planktonic cells. However, these differences are negligible at 48 hpi. Besides, the expressions of inlA and lap mRNA in sessile Lm from intestinal content are about 6.0- and 280-fold higher than the sessle inoculum, respectively, suggesting sessile Lm can still upregulate virulence genes shortly after ingestion (12 h). Similarly, exposure to simulated gastric fluid (SGF, pH 3) and intestinal fluid (SIF, pH 7) for 13 h shows equal reduction in sessile and planktonic cell counts, but induces LAP and InlA expression and pathogenic phenotypes. Our data show that the virulence of biofilm-isolated Lm is temporarily attenuated and can be upregulated in mice during the early stage (12–24 hpi) but fully restored at a later stage (48 hpi) of infection. Our study further demonstrates that in vitro cell culture assay is unreliable; therefore, an animal model is essential for studying the pathogenesis of biofilm-isolated bacteria.