Host–pathogen interface

When a pathogenic microbe faces its host cell, there may occur biochemical siganalling between them. Such cross-talk between the two can turn into a cross-fire like a war-front. In certain situations, mucous lining around the host cell may deny immediate access to the pathogen to adhere physically to the plasma membrane of the host cell. Anti-microbial peptides secreted by the host cell can damage the integrity of the approaching pathogen. Innate and cellular immunity of animal host may also neutralize the pathogens before close encounter with specific host cell. Gram-negative pathogens have an additional outer membrane - consisting largely of endotoxic lipopolysaccharide (LPS), porin, specialized outer membrane proteins - and thus are seemingly at advantage compared to Gram-positive microbes. Thus Gram-negative organisms have and additional compartment called periplasm - cellular contents between bacterial outer membrane and the inner membrane. Periplasm allows specialized capability to the Gram negative organisms, as this compartment can expand to accommodate microbial secretions; as well it can bleb out nanovesicles, called outer membrane vesicles (OMVs), transporting varied signal molecules among other cells of its own type of quorum sensing or other competing microbes to thwart them from sharing the same nutritional niche, or eukaryotic cells for inter-species or inter-kingdom interactions. OMVs, thus open a new vista in the celebrated field of membrane vesicle trafficking. In view of importance of this realization, this process was heralded as a revolutionary process of vesicular exocytosis in prokaryotes for varied purposes,including invasion of animal hosts.