IV. VIRUSES

I. BACTERIOPHAGE-INDUCED ALTERATION OF BACTERIA

Fundamental Statements for this Learning Object:

1. Lytic bacteriophages usually cause the host bacterium to lyse.
2. The added genetic information provided by the DNA of a prophage may enable a bacterium to possess new genetic traits.
3. Some bacteria become virulent only when infected themselves with a specific temperate bacteriophage. The added genetic information of the prophage allows for coding of protein exotoxin or other virulence factors.
4. Examples include the diphtheria exotoxin, streptococcal pyrogenic exotoxin (Spe), the botulism exotoxins, the cholera exotoxin, and the shiga toxin.

 

LEARNING OBJECTIVES FOR THIS SECTION

Viruses are infectious agents with both living and nonliving characteristics.

1. Living characteristics of viruses

a. They reproduce at a fantastic rate, but only in living host cells.

b. They can mutate.

2. Nonliving characteristics of viruses

a. They are acellular, that is, they contain no cytoplasm or cellular organelles.

b. They carry out no metabolism on their own and must replicate using the host cell's metabolic machinery. In other words, viruses don't grow and divide. Instead, new viral components are synthesized and assembled within the infected host cell.

c. The vast majority of viruses possess either DNA or RNA but not both.

Bacteriophage-Induced Alteration of Bacteria

1. Lytic bacteriophages (def) usually cause the host bacterium to lyse (see Fig. 1).

2. Lysogenic conversion (def) by prophages

The added genetic information provided by the DNA of a prophage (def) (see Fig. 4) may enable a bacterium to possess new genetic traits. For example, some bacteria become virulent only when infected themselves with a specific temperate bacteriophage (def). The added genetic information of the prophage allows for coding of protein exotoxin (def) or other virulence factors. The following bacterial exotoxins are a result of lysogenic conversion by a prophage:

a. the diphtheria exotoxin of the bacterium Corynebacterium diphtheriae;

b. the Streptococcal pyrogenic exotoxin (Spe) produced by rare invasive strains and scarlet fever strains of Streptococcus pyogenes;

c. The neurotoxin produced by Clostridium botulinum;

d. exfoliatin, an exotoxin that causes scalded skin syndrome, produced by Staphylococcus aureus;

e. the cholera exotoxin produced by Vibrio cholerae; and

f. the shiga toxins produced by E. coli O157:H7.

GIF animation summarizing the lysogenic life cycle of a temperate bacteriophage. by Gary E. Kaiser, Ph.D. Professor of Microbiology, The Community College of Baltimore County, Catonsville Campus This work is licensed under a Creative Commons Attribution 4.0 International License. Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html. Last updated: August, 2019 Please send comments and inquiries to Dr. Gary Kaiser

 

TPS Question

 

 

For More Information: Type I Exotoxins from Unit 3

For More Information: Type II Exotoxins from Unit 3

For More Information: Type III Exotoxins from Unit 3

 

Medscape article on infections associated with organisms mentioned in this Learning Object. Registration to access this website is free. Corynebacterium diphtheriae Vibrio cholerae enterotoxogenic E. coli Staphylococcus aureus Clostridium botulinum Staphylococcus aureus and Streptococcus pyogenes: Toxic shock syndrome

 

 

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