Page 101 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

 Some viruses escape the host cell without bursting the cell membrane but

rather bud off = lytic cycle without lysis, it is called productive cycle, e.g.

influenza.

2-Lysogenic cycle:

 The viral genetic materials enter the cell and integrate into the host DNA as

a new set of genes called prophage (provirus).

 The prophage can be transmitted to daughter cells at each subsequent cell

division. This may alter the

cell’s characteristics, but it

doesn’t destroy it.

 The phage that displays a

lysogenic cycle is called

temperate phage.

 Temperate phage is able to

undergo a lytic life cycle.

3-Cytopathic effect (CPE):

The structural changes in a host cell resulting from viral infections are collectively

called cytopathic effect. These are often of diagnostic importance.

- Such changes may include

a) Cytoplasmic changes: including inclusion bodies, cytoplasmic vacuolization,

contraction and degeneration.

b) Nuclear changes: including syncytia (formation

of multinucleated cells), nuclear inclusion bodies,

chromosomal bridges & breaks, changes in the

mitotic mechanism.

General Microbiology & Immunology (PM 401) theoretical handbook Page 90