Impedimetric screening for bacteriuria

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Abstract
A rapid, automated instrumental procedure for distinguishing urine cultures containing greater than 105 organisms/ml is described. The method is based upon measurement of changes in impedance that take place as microorganisms alter the medium''s chemical composition. Time required to detect impedance change is inversely related to the initial concentration of microorganisms in the sample. By defining an impedance-positive culture as one that gives detectable impedance change within 2.6 h, 95.8% of 1133 urine cultures tested were correctly classified as containing more than or fewer than 105 organisms/ml. Selection of a longer detection time decreases false negative results at the cost of increased false positive results. Impedance screening is compared with screening data reported in the literature using ATP detection, microcalorimetry, electrochemical measurements and optical microscopy.