From intestine to beyond: Salmonella entry factors display distinct transcription pattern upon infection in murine models

The infectious process of bacteria of the genus Salmonella requires the finely regulated use of various virulence factors. Among them, the type 3 secretion system-1 (T3SS-1) and the Rck and PagN invasins are involved in the internalization of the pathogen within eukaryotic cells, but their precise role in the host and in the pathogenic process is still poorly understood. In this study, we aimed to determine the kinetics of expression of these entry factors in a typhoid fever-like and a gastroenteritis model in mice by in vivo imaging using bioluminescent Salmonella Typhimurium reporter strains carrying chromosomal transcriptional fusions. Only pagN and T3SS-1 transcription has been clearly identified. Independently of the pathological model, the cecum was identified as the main transcription site of both pagN and the T3SS-1-encoding gene both at early and late stages of the infection. An intense transcription of pagN was also observed in deep organs in the typhoid fever-like model, while that of T3SS-1 remained quite sporadic in these organs, and mainly focused on the intestine all along the infection. This work will help to understand the respective role of these entry factors at the cellular level in the pathogenesis of Salmonella in vivo.沙门氏菌属（Salmonella）细菌的感染过程需对多种毒力因子进行精细调控。其中，3型分泌系统1（T3SS-1）以及Rck、PagN侵袭素参与了病原体侵入真核细胞的过程，但其在宿主及致病进程中的具体作用仍有待阐明。本研究旨在借助携带染色体转录融合基因的生物发光型鼠伤寒沙门氏菌（Salmonella Typhimurium）报告菌株，通过活体成像技术，解析类伤寒模型与胃肠炎模型小鼠体内上述入侵因子的表达动力学特征。目前仅明确了pagN与T3SS-1的转录情况。无论采用何种病理模型，在感染的早期与晚期阶段，盲肠均为pagN及编码T3SS-1的基因的主要转录位点。在类伤寒模型的深部器官中，同样可检测到pagN的强烈转录；而T3SS-1在这些器官中的转录则较为零星，且在整个感染周期中主要局限于肠道组织。本研究将有助于在细胞层面揭示这些入侵因子在沙门氏菌体内致病过程中的各自功能。