BATTERIOPHAGE. — The discovery of the bacteriophage is due to the French bacteriologist d’Hérelle, who in 1917 described in the fecal filtrate of convalescents from bacillary dysentery a principle capable of dissolving cultures of dysenteric germs.
If such a lysed culture is filtered through a porcelain filter capable of retaining bacteria, the lysing principle passes into the filtrate, and if a small quantity of the latter is added to a new culture of the same germ, lysis is reproduced in II. By alternating such filtrations and passages, it is possible to transmit the lytic action from culture to culture indefinitely.
Subsequently, lytic principles of this nature, active against numerous bacterial species, were discovered not only in the feces of humans and many animals, but also in water and soil.
As to the nature of this principle, called "bacteriophage," the opinions of scholars were long divided. D’Hérelle strongly maintained that it was a true living being, capable of reproducing and parasitizing bacteria, endowed with the characteristics of filterable viruses. Other scholars, especially Bordet and his school, regarded the bacteriophage as an enzyme and thus devoid of the characteristics of living matter. This opinion, which until a few years ago enjoyed the greatest credit, was recently overturned when Ruska turned the electron microscope to the study of the bacteriophage. With the aid of this powerful research tool, he was able to confirm that d’Hérelle’s hypothesis was correct and that the bacteriophage is truly an organized, living being endowed with the properties of filterable viruses. It usually appears as extremely minute isolated granules, 8–75 mμ in diameter, more rarely as rodlets or short cylinders, or as two paired granules provided with one or two tiny cilia. These minute bodies crowd around the attacked bacterium, which rapidly undergoes lysis and disintegration. The mode of reproduction of the bacteriophage is still unknown.
The bacteriophage, like most filterable viruses, cannot be cultivated on artificial media but develops only in the presence of living bacteria. While some bacteriophages are scarcely specific and can lyse germs of several species, most are strictly specific and sometimes prove capable of lysing only one species or even a single bacterial variety. On this property some recent methods are based that aim to classify very similar germs (e.g., salmonellae) by distinguishing them precisely according to their differing sensitivity to various bacteriophages.
Bacteriophages have also been used in therapy, but generally with results that are not entirely satisfactory, both because of their frequent excessive specificity and because they rarely lyse all bacterial individuals, while those that survive give rise to a bacteriophage-resistant progeny. The significance of bacteriophages in the spontaneous healing of infectious diseases and in the elimination of pathogenic germs from water and soil is differently assessed by various scholars.