Bacteriophages are viral parasites of bacteria. They are specially adapted for attachment and penetration through the rigid cell wall surrounding most prokaryotic cells. Bacteriophage may contain either DNA or RNA as genetic material, eg, ϕ×174 (ss-DNA), T1,T2,T3 phages (ds-DNA), ϕ2 phage, ϕ6 phage (ss-RNA).