Chemical signaling between cells is an effective way to coordinate behavior within a community. Although cell-tocell signaling has mostly been studied in single species, it is now appreciated that the sensing of chemical signals across kingdoms can be an important regulator of nutrient acquisition, virulence, and host defense. In this review, we focus on the role of interkingdom signaling in the interactions that occur between bacterial pathogens and their mammalian hosts. We discuss the quorum-sensing (QS) systems and other mechanisms used by these bacteria to sense, respond to, and modulate host signals that include hormones, immune factors, and nutrients. We also describe cross talk between these signaling pathways and strategies used by the host to interfere with bacterial signaling, highlighting the complex bidirectional signaling networks that are established across kingdoms.
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