We will be hearing more and more about bacteriophage therapy in the
near future, as the deadliest of bacteria continue to mutate and gain
resistance to our latest arsenal of antibiotics. We are rapidly losing this
battle -- owing to our profligate overuse of "wonder drugs" -- and we can no
longer keep pace with the sheer efficiency of bacterial evolutionary response
to our strongest counterweapons.
A bacteriophage (phage
or bacterial virus) is a virus that infects bacteria alone. They were
discovered independently by Frederick W. Twort in Great Britain (1915) and
Félix d'Hérelle in France (1917). D'Hérelle coined the term bacteriophage,
meaning "bacteria eater".
Thousands of varieties of phage exist, each of which may infect only one
type or a few types of bacteria. Like all viruses, phages are simple organisms
that consist of a core of genetic material (nucleic acid) surrounded by a
protein coat or capsid. Their nucleic acid may be either DNA or RNA and
may be double-stranded or single-stranded. There are three basic structural
forms of phage: an icosahedral (twenty-sided) head with a tail, an icosahedral
head without a tail, and a filamentous form.
During infection a phage attaches to a bacterium and inserts its genetic
material into the cell. The injected phage material takes over the machinery
of the cells to make phage components. If of a lytic type, they then
destroy the cell, releasing new phage particles. A second, more benign type
called lysogenic phages incorporate their nucleic acid into the
chromosome of the host cell and replicate with it as a unit without destroying
the cell. However, under certain conditions lysogenic phages can be induced to
follow a lytic cycle.
Undoubtedly, bacteria and bacteriophages evolved together for a billion
years or more, each keeping up with the other in their battle for survival.
Show me one creature in God’s universe that doesn’t have a nemesis out there
who wants to kill him -- either for food, or as a nice warm host body in which
to inject and nourish his progeny. But, as Nietzsche said, whatever
doesn't kill you, makes you stronger...
Phages have played an important role in laboratory research in the 20th
century. The first phages studied were used as model systems for the study of
virus multiplication. Alfred Day Hershey
and Martha Chase used a bacteriophage in a famous experiment in 1952 which
supported the theory that DNA is the genetic material. Certain other phages
are used in recombinant DNA work. The particular phage X174 was the
first organism to have its entire nucleotide sequence determined, by Frederick
Sanger and his colleagues in
Soon after making their initial discovery, Twort and d'Hérelle began to
research the use of phages in treating human bacterial diseases such as
bubonic plague and cholera. As the biology and narrow specificity of phages
was poorly understood at the time, that work was not very successful. After
the discovery of "broad spectrum" antibiotics in the 1940s, phage therapy was
virtually abandoned except in Eastern Europe and Russia, where d'Hérelle had
traveled to continue his work and to establish new research centers.
Now, a half century after being cast aside, phages are
getting a second look as
a weapon against "superbugs" that have developed resistance to antibiotics.
Bacteria such as staphylococcus, enterococcus, and streptococcus, once
considered conquered, have remade themselves into prolific killers. Nearly
90,000 Americans died last year of hospital-acquired infections; many of these
were caused by antibiotic-resistant strains. It’s a helluva note, when our
hospitals turn out to be the riskiest, most unhealthy places to visit!
Be on the lookout for news of fresh bacteriophage research and results of
new clinical trials. Phages may well save your life someday…
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Much of this material was paraphrased from
Image at top is a depiction of a T4 phage from
http://www.mansfield.ohio-state.edu/~sabedon/. No artist credited.