Biomedical subjects
Publications and source records attributed to S J Reed.
A turbidimetric assay method applicable to virginiamycin at level ranging from 5 g/ton in feeds to 50% in a premix is described. Incubation period is 4 h. Test organism is Streptococcus faecium ATCC 8043. On 6 levels of feed-grade material, the overall mean recovery was 6.75% Standard recovery studies resulted in RSD values ranging from 2.01 to 3.88% and a mean standard recovery of 100%.
New automated and manual turbidimetric microbiological assay methods for oxytetracycline (OTC) in finished feeds and a feed premix were submitted to 17 collaborating laboratories for comparison with the official AOAC method. Six finished feeds of 50 and 100 g/ton levels and one premix containing 20 g OTC/lb were sent to the collaborators. Results were received from 12 laboratories. Six laboratories provided results derived from the Autoturb System and 7 laboratories poerformed the turbidimetric analyses manually. All 12 laboratories assayed the samples by the AOAC cylinder-plate method. Ranges of recoveraies expressed as percent were 89.5-102.0, 91.2-97.0, and 91.4-96.0 for the AOAC, Autoturb turbidimetric, and manual turbidimetric methods, respectively. Average recoveries were 96.3, 93.4, and 93.6%, respectively. The mean relative standard deviation values were 5.7, 6.3, and 7.2, respectively. There was little significant difference between the turbidimetric methods and the AOAC method; however, the turbidimetric methods were faster.
A rapid turbidimetric assay has been developed for chlortetracycline hydrochloride (CTC-HCl) in finished animal feeds and feed supplements, using Leuconostoc mesenteroides as the test organism. Two modifications are presented: The incubation period of modification 1 is 2.5 hr and the sensitivity of the assay is 0.03 microgram CTC-HCl/assay tube. Modification 2 has a sensitivty of 0.01 microgram CTC-HCl/assay tube and requires an incubation period of 3.5 hr. For 21 feed formulations, the turbidimetric method recovered 95.7% of label claim. Recoveries of CTC-HCl standards from the same feeds ranged from 93.4 to 134% with a mean of 103%. The relative standard deviation among day-to-day duplicates is 3.50% for the faster modification and 1.63% for the more sensitive modification.
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Temperature-sensitive clones have been selected from a mutagenized culture of Chinese hamster lung cells by a procedure involving bromodeoxyuridine (BrdU) incorporation and irradiation with black light. The selection procedure used in these studies was adapted from methods developed by others to yield mutants that cease DNA replication within a short time after they are transferred to nonpermissive temperature. After mutagenesis with ethyl methanosulfonate ten clones survived the selection procedure. Three of the clones (mutants) were temperature-sensitive as measured by growth properties. Two mutants ceased DNA synthesis within six hours of being shifted to 39degrees and the third mutant continued to synthesize DNA at nonpermissive temperature at a reduced rate for at least 24 hours. Thus, all three mutants survived the selection procedure for understandable reasons, since each was unable to incorporate sufficient BrdU at 39degrees to lethally protosensitize its DNA during the standard exposure period. The two mutants that cease DNA synthesis at high temperature (clones 115-47 and 115-53) also stop incorporating radioactive amino acids and uridine within six hours at 39degrees. Their complex phenotype, i.e. defective DNA, RNA and protein biosynthesis, is reversible. When these mutants were returned to 33 degrees after 8 hours at 39 degrees, both resumed DNA synthesis immediately (less than 1 hour). Reversal of defective DNA synthesis in both mutants were sensitive to drugs that inhibit protein biosynthesis specifically. Those same drugs, as well as toxic amino acids analogs, also effected a striking mutant phenocopy in wild-type cells. The phenocopy produced by amino acid analogs that are incorporated into mammalian proteins suggested that one or more proteins must be synthesized continuously to support mammalian cells engaged in programmed DNA replication.
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