Lesson 2: Public Health Microbiology

Section III: Viruses

2-14

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2-14. BACTERIOPHAGES

Certain viruses have the ability to infect bacterial cells. Such a virus is known as a bacteriophage ("bacteria eater"). Bacteriophages are lunar-lander shaped (figure 2-7(E)) viruses, the action of which is specific for any given species. In other words, coliphages attack only coliform bacteria; staphylophages attack only staphylococci; and so on. Very few bacteria (pneumococci are an example) do not have phages.

a. Action of Bacteriophages. The action of bacteriophage on a bacterial. cell is shown in figure 2-8. The virus attaches itself to the bacterial cell (figure 2-8 A), whereupon the tail penetrates the cell wall by chemical action. The DNA of the virus then flows into the bacterial cell (figure 2-8 B). At this point with some viruses the viral DNA joins (links) with the bacterial DNA. Now, whatever genetic code is carried on, the viral DNA will be translated into proteins. Many times these proteins are powerful exotoxins or destructive enzymes. If the viral DNA remains separate from the bacterial DNA then the DNA takes over the action of the cell, synthesizing hundreds of new viruses. When the numerous new phage particles have formed, the cell structure disintegrates, liberating the newly formed virus particles (figure 2-8 C).

b. Importance of Bacteriophages. Bacterial viruses occur in nature with their specific hosts. Their highly specific nature assists the bacteriologist in classifying and typing bacteria (an additional identification technique, known as phage typing). Bacteriophages are not always beneficial; in certain industries that depend upon fermentation (baking, wine making, biological, and so forth.), an infestation of bacterial virus could cause great financial loss. Many of the pathogenic effects of bacteria (enzymes and toxins) are produced only when the bacteria are infected with certain viruses.

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