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 (InlA^m) 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.

环境线索促进微生物生物膜的形成以及生理和遗传异质性。在食品生产设施中，病原体产生的生物膜是食品污染的主要来源；然而，生物膜分离的无柄细胞的发病机制尚不清楚。我们使用细胞培养和小鼠模型研究了无柄单核细胞增生李斯特菌( Lm ) 的发病机制。Lm无柄细胞表达水平降低的lap、inlA 、 hly、prfA和sigB并且在细胞培养模型中表现出比浮游细胞减少的粘附、侵袭、易位和细胞毒性。用食物、临床或鼠化-InlA (InlA ^m ) 菌株对 C57BL/6 小鼠进行口服攻击表明，在感染后 (hpi) 12 和 24 小时，感染无柄细胞的小鼠组织中的Lm负荷低于那些感染的小鼠与浮游细胞。然而，这些差异在 48 hpi 下可以忽略不计。此外，来自肠内容物的无柄Lm中inlA和lap mRNA的表达分别比无柄接种物高约 6.0 倍和 280 倍，表明无柄Lm摄入后不久（12 小时）仍可上调毒力基因。类似地，暴露于模拟胃液（SGF，pH 3）和肠液（SIF，pH 7）13 小时显示固着和浮游细胞计数同样减少，但诱导 LAP 和 InlA 表达和致病表型。我们的数据表明，生物膜分离的Lm的毒力暂时减弱，并且可以在早期阶段（12-24 hpi）在小鼠中上调，但在感染的后期（48 hpi）完全恢复。我们的研究进一步表明体外细胞培养试验是不可靠的；因此，动物模型对于研究生物膜分离细菌的发病机制至关重要。