Bacteriuria screening by direct bioluminescence assay of ATP

A direct bioluminescence assay for bacteriuria screening is described and compared with the MS-2 system (Abbott Laboratories, Irvine, Tex.) and the chemical strip, Gram smear, and calibrated-loop methods. A total of 973 specimens were tested. Unlike previously described bioluminescence methods, this test measures total ATP in urine without pretreatment of samples to remove somatic ATP. The result was compared with an ATP standard (20 ng/ml). A low result (<3% of standard) was interpreted as negative and a high result (>10% of standard) as positive. Samples with intermediate results (38% of total) were incubated at 35°C in thioglycolate broth (1:10). A 2% increase in ATP concentration was interpreted as positive. The sensitivity of this method for detecting >10⁵ pathogens per ml was 92.3% and was comparable to those of the MS-2 system (92.7%) and the Gram smear method (90.5%). The chemical strip method was less sensitive (84.0%). The direct bioluminescence method was more sensitive than were the MS-2 system and the Gram smear method for detecting low-level bacteriuria (<10³ to 10⁵ organisms per ml), primarily because of associated pyuria. Thioglycolate broth provided a suitable medium for ATP production, and 5% CO₂ decreased bacterial ATP synthesis during log-phase growth. The direct bioluminescence assay is rapid, simple, cost-effective, and reliable for bacteriuria screening.