The Occurrence of Bacteria Resistant to Penicillin, Streptomycin, and Sulfanilamide in Diluted Bull Semen

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Abstract
Diluted bull semen containing 3 mg./ml. of sulfanilamide, 500 units/ml. of penicillin, and 500 [mu]g./ml. of streptomycin was held at 5[degree]C. for 24 hrs. and then plated on heart infusion agar. Counts from 100 to 10,000/ml. were obtained when penicillinase and paraamino-benzoic acid were included in the plating medium. No increase in counts was obtained by neutralization of the streptomycin by a strongly reducing medium. Counts from individual bulls at wkly. intervals were usually similar, although there were wide variations among different bulls. Comparison of percent non-returns from semen with low and with relatively high counts of antibiotic-resistant bacteria indicated that these bacteria did not influence fertility. Sulfanilamide had little or no effect on the bacterial content of semen containing penicillin and streptomycin. The inclusion of both of the antibiotics is desirable, however, since bacteria are usually present that are resistant to one but not the other. The resistant bacteria were primarily diphtheroids and were inhibited but not killed by low concns. of penicillin; however, they were not inhibited by relatively high concns. of streptomycin.
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