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Rapid Bioluminescence Method for Bacteriuria Screening MARIE T JOURNAL OF CLINICAL MICROBIOLOGY, Apr. 1989, p. 716-720 Vol. 27, No. 4 0095-1137/89/040716-05$02.00/0 Copyright C 1989, American Society for Microbiology Rapid Bioluminescence Method for Bacteriuria Screening MARIE T. PEZZLO,* VALERIE IGE, AMELIA P. WOOLARD, ELLENA M. PETERSON, AND LUIS M. DE LA MAZA Department of Pathology, Division of Medical Microbiology, University of California Irvine Medical Center, 101 City Drive, Orange, California 92668 Received 18 August 1988/Accepted 3 January 1989 A study was performed to evaluate the UTIscreen (Los Alamos Diagnostics, Los Alamos, N. Mex.), a rapid bioluminescence bacteriuria screen. The UTIscreen was compared with three other rapid bacteriuria screens: the Bac-T-Screen (Vitek Systems, Hazelwood, Mo.), an automated filtration device; the Chemstrip LN (Boehringer Mannheim Diagnostics, BioDynamics, Indianapolis, Ind.), an enzyme dipstick; and the Gram stain. A semiquantitative plate culture was used as the reference method. Of the 1,000 specimens tested, 276 had colony counts of >105 CFU/ml by the culture method. Of these, the UTIscreen detected 96% (265 of 276) using .5% of the integrated light output of the standard reading as a positive interpretive breakpoint, the Bac-T-Screen detected 96% (266 of 276), the Chemstrip LN detected 90% (249 of 276), and the Gram stain detected 96% (264 of 276). Of the 214 probable pathogens isolated at >105 CFU/mI, the UTIscreen detected 95% (204 of 214), the Bac-T-Screen detected 98% (210 of 214), the Chemstrip LN detected 92% (198 of 214), and the Gram stain detected 98% (209 of 214). The predictive values of negative test results at >105 CFU/ml for the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain were 98, 97, 93, and 98%, respectively. The overall specificities at > 105 CFU/ml for the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain were 70, 48, 51, and 69%, respectively. There were 532 specimens with colony counts of >103 CFU/ml, and of these, the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain detected 72, 81, 76, and 73%, respectively. Of the 249 probable pathogens isolated at >103 CFU/ml, the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain detected 91, 95, 89, and 93%, respectively. The overall specificities at >103 CFU/ml for these methods were 79, 55, 57, and 78%, respectively. The cost per test for detection was approximately $1.00 to $1.20 for the UTIscreen, the Bac-T-Screen, and the Gram stain and approximately $0.50 for the Chemstrip LN. Overall, the UTIscreen is rapid and easy to perform; its sensitivity compared favorably with those of other screening methods; it had a higher specificity than the Bac-T-Screen and Chemstrip LN; and it allowed for batching of specimens. Urine specimens represent the majority of samples re- semiautomated urine screens include bioluminescence and ceived in the clinical microbiology laboratory for culture. filtration methods. These systems are more rapid (1 to 15 The laboratory faces the challenge of rapidly identifying both min) than the growth detection methods and results of both positive and negative specimens. Although the semiquanti- compare favorably (2, 5, 6, 20, 21, 24, 25). tative plate culture method allows for the isolation and The purpose of this investigation was to evaluate a biolu- enumeration of most infectious agents, it does not provide minescence method, the UTIscreen, and to compare it with for same-day reporting of negative specimens. For this other rapid bacteriuria screens: the Bac-T-Screen, an auto- reason, rapid urine screening tests have been developed. mated filtration method; the Chemstrip LN, an enzyme These tests not only provide for rapid reporting of negative dipstick method; and the Gram stain. In this study, these specimens but also have the potential of reducing the cost of methods were evaluated at various colony counts in an patient management. attempt to aid others in the selection of a laboratory ap- A number of rapid urine screens have been described (12). proach to urine screening. These include microscopic, enzymatic, filtration, and photo- metric methods. The most commonly used microscopic MATERIALS AND METHODS method is the Gram stain. As a urine screen, it is rapid, Specimens. A total of 1,000 specimens which included 688 reliable, and correlates with colony counts of >105 CFU/ml clean-voided and 312 catheterized urine specimens from (13, 22, 23). However, because the acceptable sensitivity of both inpatients and outpatients submitted to the Medical this method is at 105 CFU/ml, low-level bacteriuria may not Microbiology Laboratory at the University of California be detected. Furthermore, the accuracy is greatly dependent Irvine Medical Center were included in this study. Patients on the expertise of the reader. Enzyme dipsticks have also receiving antimicrobial therapy were not excluded. Col- been used as rapid bacteriuria screens. Although these tests lected urine was placed in a sterile tube, refrigerated (4°C), are easy to perform, the overall sensitivity of these rapid and processed within 8 h of collection. enzyme dipsticks is too low (.90%) to be used alone as urine Semiquantitative culture. A semiquantitative plate count screens (15, 25). The first generation of semiautomated as described by Clarridge et al. (3) was used as the reference bacteriuria screens include photometric methods which re- method. By using a calibrated platinum loop, a 0.001-ml quire growth of the organism for detection; therefore test sample of a well-mixed urine specimen was inoculated onto results are delayed (1 to 13 h). The second generation of a 5% sheep blood agar plate (BBL Microbiology Systems, Cockeysville, Md.) and a biplate consisting of MacConkey agar and polymyxin B-nalidixic acid blood agar (Calscott, * Corresponding author. Inc., Carson, Calif.). An additional 0.1 ml of urine was 716 VOL. 27, 1989 RAPID BACTERIURIA SCREENING BY BIOLUMINESCENCE 717 TABLE 1. Number and percentage of positive test results ranging from a trace to a 2+ intensity. For nitrite, any pink was considered positive. Culture (CFU/ No. (%) positive results by: ml) (no. of Gram stain. A sample (0.01 ml) of well-mixed uncentri- specimens) UTIscreen Bac-T-Screen Chemstrip LN Gram stain fuged urine was Gram stained and examined for the presence or absence of leukocytes and microorganisms. The criterion (90) 264 (96) >105 (276) 265 (96) 266 (96) 249 for a positive Gram stain was the presence of one or more 1031-i1 (256) 116 (45) 164 (64) 156 (61) 124 (48) 10'-103 (175) 56 (32) 87 (50) 77 (44) 46 (26) bacterial cells and one or more leukocytes per oil immersion <10' (293) 44 (15) 124 (42) 125 (43) 58 (20) field, which has been reported to correlate with -10' CFU/ ml and pyuria, respectively (3). Predictive value. Predictive values were calculated by the method of Ransohoff and Feinstein (17). The sensitivity, inoculated onto a 5% sheep blood agar plate. Cultures were specificity, and predictive values of positive and negative incubated overnight at 35°C and examined for the number test results were calculated as follows: sensitivity = TP/(TP and types of organisms present. Organisms considered con- + FN); specificity = TN/(TN + FP); predictive value of a taminants were diphtheroids, lactobacilli, viridans group positive test = TP/(TP + FP); and predictive value of a streptococci other than group D, and mixed cultures from negative test = TN/(TN + FN), where TP is true-positive, voided urine specimens. TN is true-negative, FP is false-positive, and FN is false- UTIscreen. Urine specimens were processed according to negative. the instructions of the manufacturer (Los Alamos Diagnos- Time and cost analysis. An analysis of cost per test was tics, Los Alamos, N. Mex.). A sample of well-mixed urine done by calculating the cost of materials routinely used and (0.025 ml) was added to a tube containing dehydrated technical time incurred in our laboratory. The average cost somatic cell releasing agent. Additionally, 0.025 ml of the per specimen was calculated by including both positive and ATP standard was added to a clean polystyrene tube (12 by negative screen results. The cost of detection included 50 mm). The tubes were incubated for 15 min at room material costs and technical time. Technical time was calcu- temperature. Each tube was then placed into the specimen lated based on current College of American Pathologists well of the Luminometer 535 (Los Alamos Diagnostics), and workload units (4) when available or the average time both luciferin-luciferase reagent and bacterial releasing agent required to process 20 specimens by a test method. were added automatically. The integrated light output was displayed on the instrument front panel and also recorded as RESULTS part of the automatic sequence. In this study, the data were analyzed using 25% integrated light output of the standard Distribution of test results. A total of 1,000 clean-voided as a positive test. and catheterized urine specimens were evaluated. There Bac-T-Screen. Urine specimens were processed with the were 276 (27.6%) specimens with colony counts of >10' Bac-T-Screen according to the instructions of the manufac- CFU/ml by the standard semiquantitative plate culture turer (Vitek Systems, Hazelwood, Mo.). A 1-ml sample of method. Of these, the UTIscreen detected 265 (96%) com- well-mixed urine was added to the active barrel of the pared with 266 (96%) by the Bac-T-Screen, 249 (90%) by the instrument. The reagents, 3 ml of urine diluent (14.5% acetic Chemstrip LN, and 264 (96%) by the Gram stain (Table 1). acid), 3 ml of safranin O dye, and two additions each of 3 ml Overall, 226 (82%) were detected by all methods, and at least of decolorizer (2.4% acetic acid), were added automatically.
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