Bacteriophage-Induced Alteration of Bacteria

IV. VIRUSES

I. BACTERIOPHAGE-INDUCED ALTERATION OF BACTERIA

The overall purpose of this Learning Object is to introduce various mechanisms by which bacteriophages harm or alter their host.

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 phages (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 phage (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.

TPS Question

For More Information: Type I Exotoxins from Unit 2

For More Information: Type II Exotoxins from Unit 2

For More Information: Type III Exotoxins from Unit 2

E-Medicine 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

QUIZ YOURSELF ON THIS SECTION

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