Enumeration of Bacterial Cell Numbers and Detection of Significant Bacteriuria by Use of a New Flow Cytometry-Based Device

Abstract

A new, automated flow cytometry-based urine bacterium analyzer (UBA) was developed. We assessed the UBA for linearity of measurement, reproducibility of results, carryover rate, and correlation of measured results with those determined by urine culture. We also evaluated its ability to screen urine samples for significant bacteriuria. The UBA showed excellent linearity and a minor carryover rate. Results from the UBA were highly reproducible, and in between-run precision assays, the coefficients of variation for the UBA results were smaller than those for the urine culture results. Two hundred seventy-three urine specimens from patients attending the outpatient clinics of two university-based hospitals were examined. The results for the UBA were compared with those for urine culture. The UBA detected significant bacteriuria with a sensitivity of 96.6%, a specificity of 79.9%, a positive predictive value of 57.0%, a negative predictive value of 98.8%, a false-positive rate of 15.8%, a false-negative rate of 0.7%, and an accuracy of 83.5%. These results were comparable to or better than those obtained with previously reported screening procedures. The UBA can perform accurate enumeration of bacterial cells automatically in 90 seconds and can be used for the screening of significant bacteriuria.Although the standard method for diagnosis of urinary tract infection is quantitative urine culture and identification of bacteria, fewer than 30 percent of urine samples sent to the laboratory are proven positive (6). Thus, a rapid screening method is required to reduce these time-consuming and expensive procedures. We have reported that the flow cytometrybased automatic urinalysis device UF-50 can detect significant bacteriuria with a false-negative rate (FN) of 5.4% (7). For the ideal screening method, the false-negative rate should be lower. For this purpose, we developed a new device to perform enumeration of bacterial cells in urine by using flow cytometry technology equipped with a semiconductor laser. In this paper, we evaluated the linearity and reproducibility of the measurement and compared the measured results with those from the conventional urine culture method using clinical urine specimens. We also evaluated the feasibility of using this new device to predict the results of urine culture. MATERIALS AND METHODSBacterial strains and media. Four bacterial strains, Escherichia coli ATCC 11775, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 29213, and Enterococcus faecalis ATCC 29212, were purchased from ATCC.Clinical specimens. Urine specimens were collected from patients attending the outpatient clinics of two university hospitals. Patients with urinary diversions or orthotopic neobladder with bowel segments were excluded. Also excluded were the patients who had fistulas between the urinary tract and bowels.A sterile plastic container with a wide opening was used to collect midstream urine. Female patients were asked to wipe their external genitalia with a wet tissue before urinating. Ten millilit...

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