Bacterial immune systems.

Bacterial immune systems encompass the multi-layered defense mechanisms that bacteria develop against bacteriophages and mobile genetic elements, such as plasmids. This review covers bacterial innate defense systems (surface defenses, superinfection exclusion, restriction-modification, abortive infection, and toxin-antitoxin systems), CRISPR-Cas-mediated adaptive immunity, and the escape strategies used by phages to overcome these defenses (genome modifications, anti-restriction proteins, and anti-CRISPR factors). Emerging evidence also highlights the role of outer membrane vesicles (OMVs) in anti-phage defense and their translational potential as vaccine and delivery platforms. In this context, a better understanding of bacterial defense systems contributes to the development of biotechnology and medical applications such as CRISPR technologies, diagnostic approaches, and phage therapy.