Effect of Neomycin on Two Species of Free-Living Protozoa

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Abstract
Changes in cell nos. of Tetrahymena geleii H, and Euglena gracilis var. bacillaris (green and colorless strains), when grown in Bacto casitone - Bacto yeast extract medium with various concns. of neomycin, were investigated. Tetrahymena was stimulated with 25-250 U./ml. Cell nos. in the medium containing 25 U./ml., after a 72-hr. incubation period, exceeded controls by 71%. Ciliates grown without neomycin were larger than those from cultures containing the antibiotic; at 250 U./ml. the difference in avg. length amounted to as much as 100%. There were fewer ciliates in cultures with 400 or more U./ml. than in controls. The colorless flagellate was more sensitive than Tetrahymena. Inhibition of pop. growth occurred at levels about 50 U./ml.; when incubated for 210 hrs. in 400 U./ml., the inhibition was 99% complete. No significant difference was noted in the degree of inhibition exhibited on the green and colorless strains of Euglena. The inhibitory effect of neomycin was compared with results reported for other antibiotics on these 2 spp. of free-living protozoa.

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