The use of beta-galactosidase gene fusions to screen for antibacterial antibiotics.

The desirable features for a screening assay to detect antibacterial antibiotics include 1) high specificity for the desired antibiotic type 2) high sensitivity 3) lack of interference by other compounds likely to be associated with the antibiotic of interest and 4) ease of operation to allow a large number of samples to be tested. These characteristics are largely found in screens employing strains carrying fusions between antibiotic induced promoters and the structural genes for Escherichia coli beta-galactosidase. Screens were designed based upon fusions with three antibiotic induced promoters: the tetracycline induced tetA/tetR promoter from transposon Tn10, the erythromycin induced promoter from the Staphylococcus aureus ermC erythromycin-resistance gene and the chloramphenicol induced promoter from the S. aureus cat86 chloramphenicol-resistance gene. Because there have been no reports of vancomycin induced resistance determinants, a Tn903 random gene fusion pool was screened to isolate a vancomycin induced gene fusion. This gene fusion was induced fairly specifically by glycopeptide antibiotics and the fusion was used as the basis for a glycopeptide screen.