MYSTERIOUS VIRUS PREYS ON BACTERIA.

Horowhenua Chronicle, 12 July 1935, Page 3

MYSTERIOUS VIRUS PREYS ON BACTERIA.

DAIRY RESEARCH INSTITUTE DISCOVERY. FURTHER INFORMATION AVAILABLE. The attention of the cheese industry in New Zealand is at present concentrated on the remarkable discovery by the Dairy Research Institute, Palmerston North, of a bacteriophage in starters—a discovery that seems destined to play a revolutionary part in future cheese-making operations. A bacteriophage is a germ which produces such a powerful inhibitory substance that it practically prevents the growth of another. This bacteriophage condition has be2n known in medicine for many years,, bu-fc. it is the first time on record that its presence has been revealed in any part of the world in starter cultures. A recently published bulletin I>y the Department of Scientific and Industrial Research gives some additional information regarding this remarkable discovery. The first observation- of a form of transmissible lysis among bacteria was made by Twort in 1915. d'Hereiic (1917) encountered the phenomenon independently. He drew more general attention to it and developed a theory to account for the action of the lytic agent which he termed bacteriophage. Since that time innumerable observations of bacteriophage (or phage) phenomena in many species of bacteria Jiave been reported; and several conflicting theories of the nature of phage have been developed. It is not necessary to discuss these here, but simply to say that phage acts in most respects as though it were a virus parasitic upon the bacterial species or straiu which shows the characteristic re action. The phage multiplies with the organisms and at a certain stage induces an almost complete and rapid lysis or dissolution of the bacterial cell's. A very small amount of a lysed culture suffices to restart the chain of events in a fresh culture, and thus the phage is transmissible in series apparently ad infinitum. Phages are most common among the eolon-typhoid-dysentry group of organisms, although phage action has been reported with most other types. Burnet (1930) gives a very complete ac- j count of • the observations. Phages against streptococci have, however, been reported on very few occasions, and only ona (Hadley-and Dabney, 192(5), so far as the authors are aware, against streptococci of the lactic-acid

group which sire used as "starter" cultures in the dairy industry. Work at '.lie Dairy Research Institute has lately led to "the discovery that a phage active against lactic streptococci is occasionally present in cultures used as starters. Dr. 11. R. Whitehead in 19:34 reported the occurrence of ji curious phenomenon in starter cultures whereby aeration of the - milk medium sometimes led to a sudden failure in either one or two generations of the growth of the starter organisms. Strong evidence has now been obtained that this phenomenon is essentially due to the presence of a streptococcal phage in the affected starter culture. From an aerated culture which had shown the sudden failure previously described, a phage \va.isolated by the usual methods, it has been .propagated in serial cultures tor several weeks, and has been obtained in a bacteria-free filtrate in such a strength that a dilution of the filtrate in milk to the extent of one part in several hundred thousand million parts suffices to show the characteristic lysis with a susceptible streptococcus. On a solid medium the phage, acting upon the streptococci, gives the classical ;ippearance of "plaques" wheie the lytic action has spread irom the hypothetical phage "corp-ssci.es'' t > fo; : circular, clear space:; in a mass ui confluent, growth. The of r.ction in connection with the problem of vitality in cheese-starters can hardly be ! overemphasised. Although the one phage so far isolated seems to be speci- , fie in its action to one strain of strep- i toeocci, there seems little doubt that phages have been concerned in previous cases of starter failure which were ■ proved to be caused by aeration of . the milk medium. Where a phage is , present in a culture it appears tinder i the usual conditions of growth to give little evidence of its presence; the effect of aeration seems to be a "flareup" of the phage. The mechanism of i this action is at present quite obscure. From a practical point of view it is • necessary to find some method of eiim- j inating the phage or of using an or- | ganisiu immune to its action. The isolation of ' phage-immune varieties j seems to offer the greater promise or ( success, and progress has already been j made in that direction.