Metabolism. Antibiotics and Pesticides

And yet the greatest successes of chemotherapy were not to lie with synthetic compounds like arsphenamine and sulfanilamide but with natural products. A French-American microbiologist, Rene Jules Dubos (1901- ), was interested in soil microorganisms. After all, the soil received the dead bodies of animals with every conceivable disease and, except in rare cases, it was not itself a reservoir of infection. Apparently, there were agents within the soil that were antibacterial. (Such agents later came to be called "antibiotics" meaning "against life.")

In 1939, Dubos isolated the first of the antibiotics, "tyrothricin," from a soil bacterium. It was not a very effective antibiotic, but it revived interest in an observation made by a Scottish bacteriologist, Alexander Fleming (1881-1955), over a decade earlier.

In 1928, Fleming had left a culture of staphylococcus germs uncovered for some days. He was through with it and was about to discard the dish containing the culture when he noticed that some specks of mold had fallen into it and that around every speck, the bacterial colony had dissolved away for a short distance.

Fleming isolated the mold and eventually identified it as one called Penicillium notatum, a mold closely related to the common variety often found growing on stale bread. Fleming decided that the mold liberated some compound which, at the very least, inhibited bacterial growth. He called the substance, whatever it might be, "penicillin." He investigated it to the point of showing that it would affect some bacteria and not others and that it was not harmful to white blood corpuscles and, therefore, possibly not harmful to other human cells. Here he had to let his efforts stop.

However, 1939 saw interest in antibiotics (of which penicillin was clearly an example) bound upward, thanks to Dubos' work. In addition, the coming of World War II meant that any weapon to combat infected wounds would be welcome. An Australian-English pathologist, Howard Walter Florey (1898- ), together with a German-English biochemist, Ernst Boris Chain (1906- ), tackled the problem of isolating penicillin, determining its structure and learning how to produce it in quantity. By war's end, they headed a large Anglo-American research team and succeeded brilliantly. Penicillin became and even yet remains the work horse of the doctor's weapon against infection.

After the war, other antibiotics were sought for and found. The Russian-American bacteriologist, Selman Abraham Waksman (1888- ), went through soil microorganisms as systematically as Ehrlich had gone through synthetics. In 1943, he isolated an antibiotic that was effective against many bacteria that were unaffected by penicillin. In 1945 it went on the market as "streptomycin." (It was Waksman, by the way, who coined the word "antibiotic.")

In the early 1950s, the "broad-spectrum antibiotics" (those affecting a particularly wide range of bacteria) were discovered. These are the "tetracyclines," best known to the public by such trade-marks as "Achromycin" and "Aureomycin."

Bacterial diseases have been brought under control, as a result of the discovery of antibiotics, to a degree that would have seemed overoptimistic only a generation ago. Nevertheless, the future is not entirely rosy. Natural selection marks for survival those strains of bacteria that have a natural resistance to antibiotics. Therefore, with time, particular antibiotics become less effective. New antibiotics will certainly be discovered so that all will not be lost. Nevertheless, all will not be won either, and may never be.

The various chemotherapeutic agents do not, in general, affect viruses. These multiply inside living cells and can be killed by chemical attack only if the cell itself is killed. A more indirect attack, however, may be successful, for a chemical may kill not the virus itself but the multicellular creature that carries the virus.

The virus of typhus fever is carried by the body louse, for instance, a creature much harder to get rid of (since it is so closely bound to the unwashed, old-clothed human body) than is the free-living mosquito. Yellow fever and malaria can be handled by mosquito-control but typhus fever remained mightily dangerous and in Russia and the Balkans during World War I, it was more deadly to both sides, on occasion, than the enemy artillery was.

In 1935, however, a Swiss chemist, Paul Muller (1899- ), began a research program designed to discover some organic compound that would kill insects quickly without seriously affecting other animal life. In September 1939, he found that "dichlorodiphenyltrichloroethane" (usually abbreviated as "DDT"), first synthesized in 1873, would do the trick.

In 1942, it began to be produced commercially and, in 1943, it was used during a typhus epidemic that broke out in Naples soon after it had been captured by Anglo-American forces. The population was sprayed with DDT, the body lice died, and for the first time in history, a winter epidemic of typhus was stopped in its tracks. A similar epidemic was stopped in Japan in late 1945, after American forces had occupied the nation.

Since World War II, DDT and other organic insecticides have been used against insects not only to prevent disease but to keep down the havoc they wreak against man's food crops. Weed killers have also been devised and these may be lumped with insect killers under the heading of "pesticides."

Here again, insects develop resistant strains and particular pesticides become less effective with time. In addition, many fear that the indiscriminate use of pesticides needlessly kills many forms of life that are not harmful to man, and upsets the balance of nature in a way that will, in the end, do far more harm than good.

This is a serious problem. The study of the interrelationships of life forms ("ecology") is a difficult and intricate one and much remains to be understood here. Mankind is continually altering the environment in ways that are intended for short-term benefit, but we can never be entirely sure that the distortions introduced into the web of life, even when seemingly unimportant, may not be to our long-term harm.

 






Date added: 2023-02-03; views: 194;


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