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Effect of Antibiotics on Rats Fed Amino Acid-Supplemented Rice Diets

National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Public Health Service, Federal Security Agency, Bethesda, Maryland

Penicillin and aureomycin added to a lysine-threonine-supplemented rice diet with a nitrogen content equivalent to 6.17% protein produced a growth response in weanling rats approximately equal to the growth obtained with diets containing 15% casein. Penicillin generally gave the greater growth stimulation. Chloromycetin, bacitracin, streptomycin, and terramycin had little or no effect in this diet. Most of the growth-stimulating effect of the antibiotics occurred during the first 10 weeks after weaning. A basal 90% rice diet without supplementary amino acids gave significantly greater growth when each of the above-mentioned antibiotics, except chloromycetin, was added singly. Vitamin B₁₂ did not improve any of these diets except the lysine-threonine-supplemented rice diet plus aureomycin. However, vitamin B₁₂ and urea added to the lysine-threonine-supplemented rice diet gave a growth response equivalent to that obtained with the antibiotic-supplemented rice-lysine-threonine diet. This response was not obtained in the absence of vitamin B₁₂.

The organ: body weight ratios were the same in animals with and without antibiotics, indicating that the antibiotics produced a general increase in growth.

The protein efficiency ratios of rats receiving the rice-lysine-threonine diet and an antibiotic were much better than the ratios of the animals receiving the same diet without an antibiotic.

Manuscript received 24 November 1952.