Determination of factors affecting gene regulation and/or gene replication

A method for determining the presence or amount of at least one inhibitory factor in the sample to be tested, wherein the inhibitory factor inhibits one of more of DNA synthesis, transcription of DNA, translation of RNA, cell wall synthesis, cell membrane function or metabolic functions which participate in or influence these processes, said method comprising:

• a) incubating a sample to be tested with a population of transformed cells for a period sufficient to allow the inhibitory factor, if present in the sample, to affect said cells, said cells being transformed with a high copy number recombinant DNA plasmid containing a sequence encoding a marker protein which is detectable when expressed, said sequence being coupled to a regulatable promoter such that expression of said marker protein is inducible by an exogenous stimulus;
• b) then applying said exogenous stimulus to said population of cells in an amount sufficient to induce expression of said marker protein in the absence of the inhibitory factor;
• and
• c) determining the amount of said marker protein expressed by said population of cells, the amount of the inhibitory factor in the sample being correlated with a reduction in the amount of said marker protein produced compared to the amount of said marker protein produced by a like cell population by application of a like amount of exogenous stimulus in the absence of the sample.

A method for determining the presence of at least one inhibitory factor selected from the group consisting of ampicillin, chloramphenicol, oxytetracycline, streptomycin, erythromycin, ofloxacin, ciprofloxacin, actinomycin and trimethoprim in a sample of a biological fluid selected from the group consisting of blood, plasma, serum, urine, semen and milk, said method comprising:

• a) obtaining a population of cells transformed with a high copy number recombinant DNA plasmid containing a sequence encoding luciferase, wherein said sequence is coupled to a regulatable promoter such that expression of said sequence is inducible by application of a chemical inducer to cells containing said plasmid;
• b) incubating said sample with said cell population in a medium suitable for growth of said cells for a period sufficient to allow said inhibitory factor if present to affect said cells;
• c) then applying said chemical inducer to said cells in an amount which in the absence of said inhibitory factor is sufficient to induce expression of said sequence;
• and
• d) determining the amount of luciferase expressed by said cell population, the amount of said inhibitory factor in said sample being correlated with the reduction in the amount of luciferase produced relative to the amount of luciferase produced by a like cell population by application of a like amount of said chemical inducer in the absence of said sample.