4 医学微生物学Phage.pdf

Phage • Did you know that there are viruses that are also infected with bacteria? • What is the name of this virus and what are its characteristics? The concept and characteristics of phage Bacteriophage (phage) is a virus that infects bacteria, fungi, actinomycetes or spirochetes. Its size is small and can pass through the bacterial filter; There is no complete cell structure, which is mainly composed of capsid (protein) and nucleic acid. It can only replicate and proliferate in living microbial cells. It is a kind of specialized intracellular parasitic microorganism. Bacteriophages are widely distributed. Section 1 Biological characteristics of bacteriophages 1. Form and structure. There are three basic forms of bacteriophages, namely, tadpole, microsphere and rod. Most bacteriophages are tadpole-shaped. • Structure: consists of the head and tail; • Chemical composition: proteins and nucleic acids; • Nucleic acid type: DNA or RNA, the DNA of most DNA phage is linear double-strand; • The phage is antigenic; • Resistivity: Generally stronger than bacteria. Section 2 Virulent phage Phage can be divided into two types: 1. Virulent phage: can replicate in the host bacteria, produce many progeny phage, and eventually lyse the bacteria. 2. Temperate phage or lysogenic phage: The phage genome is integrated into the host chromosome, does not produce progeny phage, and does not cause bacterial lysis, but phage DNA replicates as the bacterial genome replicates. And distributed to the genome of progeny bacteria as the bacteria divide 。 Replication cycle of Viral phage The proliferative process (replication cycle or lysis cycle) of the toxic phage in the host bacteria includes four stages of adsorption, penetration, biosynthesis, maturation and release. Several no