Bacteriophage therapy in humans

Bacteriophages (or phages) have been known to the scientific and medical literature for over a hundred years. Bacteriophages are viruses that infect only bacteria and do not replicate outside their host. The classification of bacteriophages is based on their type of nucleic acid (ssRNA, dsRNA, ssDNA, or dsDNA), capsid structure composed of structural proteins, their life cycle (lytic or lysogenic), and bacterial target. Phages encompass two main states: a lytic (or virulent) state, characterized by virion production that lyses the host or a lysogenic (or temperate) state in which only the phage nucleic acid is replicated but no new virions are formed. The expanding knowledge about phage–bacteria interactions has led to new fundamental findings that are now widely used in molecular biology techniques (restriction-modification systems and clustered regularly interspaced short palindromic repeats-CRISPR-Cas systems enabling DNA editing, a phage-display method for creating humanized antibodies).