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Chapter 23 : Bacterial Responses to the Host Cell
Category: Microbial Genetics and Molecular Biology
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This chapter presents the stress conditions experienced by bacteria inside host organisms and the specific bacterial stress responses, with focus on the responses on a cellular level, especially for the subset of bacterial pathogens that have developed an intracellular lifestyle within host cells. It focuses on the integrated responses of extracellular bacteria or intracellular bacteria environments within the host. A section presents the specific conditions that are acting on bacteria during colonization of a host organism or the interaction with host cells. Cathelicidins possess an amino-terminal part called cathelin that contains an SRC, homology three-domain, required as signal for the peptide to be cleaved, activated, and secreted. The antibacterial activity resides in the carboxy-terminal part which binds to polyanionic surfaces such as lipopolysaccharides (LPS) and teichoic acids. Biofilms are multicellular microbial communities that can form in the external environment, on abiotic surfaces, as well as on host surfaces and within host cells. Different groups of molecules secreted by host cells have antibacterial functions and are responsible for activation of bacterial responses. After phagocytosis by, or adhesion to and invasion of, host cells, bacteria must adapt to the new environments inside the host cells.
Model of host and environmental factors acting on extracellular bacteria within a host organism (a) and within a host cell (b).
Regulatory circuits in Salmonella enterica responding to signals from the host. Two-component systems such as PhoPQ, PmrAB, or BarA/SirA are required to sense and integrate host-derived environmental signals. This results in the expression of specific virulence genes as well as in modification of bacterial envelope.