Increased sensitivity and discrimination in screening through an immobilized-resin microbiological assay method

Summary Problems with present bioactive microbial product screening techniques include low sensitivity and insufficient discrimination capabilities. These problems are addressed by our new immobilized-resin microbiological assay. This technique concentrates bioactive samples on macroporous polymeric resins that are immobilized in hydrogel beads. These beads are then subjected to elution in the wells of an agar diffusion microbiological assay medium. With a strong base anion exchanger, the sensitivity to ampicillin of the -lactam-supersensitiveEscherichia coli mutant ESS-22-31 was increased 10-fold. Similar increases in sensitivity were obtained in the detection of streptomycin using a weak acid cation exchanger withBacillus subtilis and for cycloheximide by a neutral resin andSaccharomyces cerevisiae NRRL-Y-139. A judicious choice of resin type and eluent permitted a selective sensitivity increase based on the charge or hydrophobic nature of the desired product. This selectivity imparts a discrimination capability to the technique.