Lytic phages are more suitable for phage therapy. Bacteriophages, often just called "phages", are viruses that parasite bacteria and archaea. Well studied examples are the viruses that infect bacteria, known as bacteriophages (or simply phages). Bacteriophages, known as phages, are a form of viruses. Mechanisms involving penetration of the phages nucleic acid are specific for each phage. The tail fibers of some bacteriophages, especially the T4-like phages, are modified peplomers. E. coli is more resistant to T7 than to some other similar phages. Salvador Luria also showed that bacterial resistance to viruses (phages) is genetically inherited. For example, T7 phages have two operons. Lysogenized bacteria are resistant to superinfection by same or related phages. Rho-dependent terminators are found in bacteria and phages. AEP multifutional primases also appear in bacteria and phages that infect them. CRISPR/Cas can immunize bacteria against certain phages and thus halt transmission. However, the host ranges of most "Streptococcus" phages have not been investigated systematically. The life cycle of lambda phages is controlled by cI and Cro proteins.