Enterohemorrhagic Escherichia coli (EHEC) colonize intestinal epithelium by generating characteristic attaching and effacing (AE) lesions. They are lysogenized by prophage that encode Shiga toxin 2 (Stx2), which is responsible for severe clinical manifestations. As a lysogen, prophage genes leading to lytic growth and stx2 expression are repressed, whereas induction of the bacterial SOS response in response to DNA damage leads to lytic phage growth and Stx2 production both in vitro and in germ-free or streptomycin-treated mice. Some commensal bacteria diminish prophage induction and concomitant Stx2 production in vitro, whereas it has been proposed that phage-susceptible commensals may amplify Stx2 production by facilitating successive cycles of infection in vivo. We tested the role of phage induction in both Stx production and lethal disease in microbiome-replete mice, using our mouse model encompassing the murine pathogen Citrobacter rodentium lysogenized with the Stx2-encoding phage Φstx_2dact. This strain generates EHEC-like AE lesions on the murine intestine and causes lethal Stx-mediated disease. We found that lethal mouse infection did not require that Φstx_2dact infect or lysogenize commensal bacteria. In addition, we detected circularized phage genomes, potentially in the early stage of replication, in feces of infected mice, confirming that prophage induction occurs during infection of microbiota-replete mice. Further, C. rodentium (Φstx_2dact) mutants that do not respond to DNA damage or express stx produced neither high levels of Stx2 in vitro or lethal infection in vivo, confirming that SOS induction and concomitant expression of phage-encoded stx genes are required for disease. In contrast, C. rodentium (Φstx_2dact) mutants incapable of prophage genome excision or of packaging phage genomes retained the ability to produce Stx in vitro, as well as to cause lethal disease in mice. Thus, in a microbiome-replete EHEC infection model, lytic induction of Stx-encoding prophage is essential for lethal disease, but actual phage production is not.

肠出血性大肠杆菌(EHEC) 通过产生特征性的附着和消失 (AE) 病变而定植于肠上皮。它们被编码志贺毒素 2 (Stx2) 的原噬菌体溶原，导致严重的临床表现。作为一种溶原，导致裂解性生长和stx2表达的原噬菌体基因受到抑制，而对 DNA 损伤响应的细菌 SOS 反应的诱导会导致裂解性噬菌体生长和 Stx2 产生，无论是在体外还是在无菌或链霉素处理的小鼠中。一些共生细菌在体外减少原噬菌体诱导和伴随的 Stx2 产生，而有人提出，噬菌体敏感的共生菌可能通过促进体内连续感染循环来放大 Stx2 产生。我们使用包含用Stx2 编码噬菌体 Φ stx _2dact溶原化的鼠类病原体柠檬酸杆菌的小鼠模型，测试了噬菌体诱导在微生物组丰富的小鼠中​​ Stx 产生和致死性疾病中的作用。该菌株在小鼠肠道上产生类似 EHEC 的 AE 损伤，并引起致命的 Stx 介导的疾病。我们发现致命的小鼠感染不需要 Φ stx _2dact感染或溶原共生细菌。此外，我们在受感染小鼠的粪便中检测到了可能处于复制早期阶段的环状噬菌体基因组，证实了在微生物群丰富的小鼠感染期间发生了原噬菌体诱导。此外，C . 对 DNA 损伤不产生反应或表达stx 的啮齿类动物(Φ stx _2dact ) 突变体在体外既不产生高水平的 Stx2 ，也不在体内产生致命的感染，这证实了 SOS 诱导和噬菌体编码的stx基因的伴随表达是疾病所必需的。相比之下，C . 啮齿类动物(Φ stx _2dact ) 突变体无法切除原噬菌体基因组或包装噬菌体基因组，但保留了体外产生 Stx 的能力，并在小鼠中引起致命疾病。因此，在充满微生物组的肠出血性大肠杆菌感染模型中，编码 Stx 的原噬菌体的裂解诱导对于致死性疾病至关重要，但实际的噬菌体产生却并非如此。