Bacterial intracellular pathogens: Offense and defense strategies

Abstract

The invasion of unicellular organisms into other organisms’ cells is widespread among bacteria, protozoa, and fungi. This phenomenon is most often manifested as intracellular parasitism, resulting in serious diseases in humans, animals, and plants. Intracellular pathogen species include about 20 bacterial taxa that can cause serious diseases in humans and animals, such as tuberculosis, leprosy, typhus, salmonellosis, brucellosis, trachoma, dysentery, and other. This review considers in detail the survival strategies of various intracellular bacterial pathogens: their mechanisms of interaction with the host cell membrane, techniques of intrusion into the host cell, survival strategies within the host cell, and mechanisms to avoid host immune responses. We also discuss the strategies of latent persistence of certain bacterial intracellular pathogens, which permit them to survive in the host organism in an inactive form for a long time under conditions of high immune pressure and become rapidly reactivated when the host immune-response levels are reduced.