Abstract
We start by being thankful for the opportunity to respond to the letter by Wood and Lee (1) and clarify several points. We strive to cite the most pertinent literature, although one also has to deal with space constraints. Hence, in several instances, reviews were cited instead of primary literature (e.g., we cited the work of Stevens and Frankel [2] instead of the whole primary literature characterizing EHEC’s type 3 secretion system [T3SS] and attaching and effacing [AE] lesion formation). We also report in our paper (3) that indole was first recognized as a signal by Wang et al. (4), not by Lee at al. (5, 6) as stated by Drs. Wood and Lee in their letter. We also note that we cited the report of Bansal et al. (7) with regard to indole’s role in signaling to mammalian cells and fortifying barrier function. Drs. Wood and Lee wrote, > “With regard to the mechanism reported by Kumar and Sperandio for sensing indole through the histidine kinase sensor CpxA of EHEC (3), it is important to note that this was discovered 14 years earlier for E. coli by Hirakawa et al. (8). These researchers found that indole sensing in commensal E. coli requires the BaeSR and CpxAR two-component systems. Unfortunately, this contribution was not cited by Kumar and Sperandio (3) [our reference numbers].” In their paper, Hirakawa et al. (8) state, > “… on the other hand, the induction of acrD and mdtA was mediated by BaeSR and CpxAR, two component systems. Interestingly, CpxAR system-mediated induction required intrinsic baeSR genes, whereas BaeSR mediated induction was observed in the cpxAR gene deletion mutant.” In their paper, Hirakawa et …
Highlights
“With regard to the mechanism reported by Kumar and Sperandio for sensing indole through the histidine kinase sensor CpxA of Escherichia coli (EHEC) [3], it is important to note that this was discovered 14 years earlier for E. coli by Hirakawa et al [8]
As published in our paper [3], “The CpxAR system is known to be activated by envelope perturbations; at high toxic indole levels (2 mM), an E. coli cpxR mutant is responsive to indole, because of perturbations of membrane integrity [9].”
We show genetically and biochemically that CpxA is a sensor for indole, using an indole concentration (500 M) that does not affect growth or perturb membrane integrity
Summary
“With regard to the mechanism reported by Kumar and Sperandio for sensing indole through the histidine kinase sensor CpxA of EHEC [3], it is important to note that this was discovered 14 years earlier for E. coli by Hirakawa et al [8]. Concerning confusion among pathovars, we point out that in the introduction of the Bansal et al paper [10], the authors cite Giron et al.’s paper [14] where they state, “An EHEC luxS mutant that is deficient in the synthesis of AI-2 and AI-3 demonstrated markedly decreased expression of flagella and motility genes required for adherence to epithelial cells.
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