Most persons are not fully aware that a large part of the American agricultural revolution of the past several decades has consisted of adding antibiotic drugs to livestock feeds to enhance the growth of the animals. Since the 1950's, when antibiotics were discovered to promote growth, antibiotics in animal feeds have become a $478 million American market. Antibiotics are added to animal feeds in most countries of the world. The antibiotic growth-promotant market promises to swell even more; American meat production will have to rise 40 percent to meet expected 1980 needs, and American farmers will be called upon more and more to provide food for a world population that is expanding twice as fast as the American one. Currently the yield from one out of five arable acres in the United States is being sent abroad. In all, growth-promotant antibiotics appear to be a boon to farmers' efforts to meet the food needs. But there is rising concern among some medical scientists, environmentalists and others that antibiotics in animal feeds may have a serious drawback. The projected drawback is that human pathogens, by being heavily and continually exposed to antibiotics in animal feeds, are building up resistance against antibiotics that used to kill them. If this is indeed the case, then these antibiotic-resistant bacteria might touch off diseases in humans that could no longer be controlled by antibiotic therapy. This concern first arose in the late 1960's, when an increase in antibioticresistant strains of bacteria-particularly of Salmonella, an organism that causes food poisoning-was noted in American and British hospitals. It is possible, of course, that these strains had developed antibiotic resistance because of heavy use of antibiotics on patients in the hospitals. However, resistant strains were also detected in meat and meat products in the United States and in Britain and in some hospital settings. So the natural conclusion of some people was that lavish use of antibiotics in animal feeds, rather than in hospitals, was why the bacteria were becoming antibiotic-resistant. The unresolved question, then, is whether heavy use of antibiotics in animal feeds allows pathogens dangerous to humans to develop antibiotic resistance. At the recent annual meeting of the American Society for Microbiology in Philadelphia, some scientists closest to the problem debated the question. If anything came out of their debate, it was that the answer simply is not yet available. Microbiologist-chemotherapist Gordon Kemp, for example, is with the American Cyanamid Co. Cyanamid has large stakes in the livestock antibiotics market. Kemp reported that even as long ago as 1960, scientists knew that antibiotic resistance could be transmitted from certain animal bacteria to others by factors. An R factor is a little piece of DNA in the cytoplasm of the bacterial cell that mediates resistance to antibiotics. But although antibiotic-resistant bacteria might be transmitted through meats to humans and cause untreatable disease, Kemp claimed there is absolutely no evidence it actually happens. Microbiologist Stanley Falkow of the Georgetown University Medical School asserted, however, that most scientists generally accept that animals can transmit antibiotic-resistant bacteria to humans. He is convinced that the overuse of antibiotics in animals might eventually compromise the effectiveness of antibiotic therapy in humans. Thomas H. Jukes of the University of California at Berkeley, the scientist first to discover the value of antibiotics to growth, contended that if antibioticresistant bacteria were a health threat, they would cause uncontrollable outbreaks of disease among livestock long before they would do so among humans. There is no evidence of such outbreaks among livestock, Jukes stated. Falkow disagreed, noting that in certain countries outbreaks of diarrhea among swine have been attributed to E. ccli bacteria that were made antibioticresistant by overexposure to animalfeed antibiotics. James Leece of the department of animal sciences at North Carolina State University presented evidence contradicting Falkow's assertion and underscoring Jukes'. Leece has eviAmerican Cyanamid Co.