Evaluation of the MS-2® and Lumac® Systems for the Rapid Screening of Urine Specimens

Abstract

The authors have evaluated the MS-2 (Abbott) and Lumac (3M) systems for the rapid screening of urine specimens for bacteriuria. These systems, which can detect significant levels of microorganisms in urine in five hours (MS-2) or 30 minutes (Lumac), were compared with a standard overnight plate culture method. Three hundred fifty-eight voided urine specimens were examined. The two systems compared equally at greater than 10(5) colony-forming units (CFU)/mL in terms of false-positive results (11%), false-negative results (2%), sensitivity (98%), specificity (approximately equal to 86%), and positive predictive value (98%), although the Lumac was found to have a lower negative predictive value (by 10%) than the MS-2. The only organism not recognized by the MS-2 at greater than 10(5) CFU/mL was a Lactobacillus; whereas the only specimens missed by the Lumac at greater than 10(5) CFU/mL were two pure cultures of Escherichia coli. At counts of greater than 10(4) to 10(5) CFU/mL, both systems missed numerous (15 of 21 isolates for the MS-2; 12 of 9 isolates for the Lumac) gram-positive cocci. The Lumac system was the most costly, being 3.6 times as expensive as the standard plate method. Although both systems greatly reduce the time required to process urine specimens, the large number of false-positive results, false-negative results at greater than 10(4) to 10(5) CFU/mL, as well as cost suggest that a careful evaluation of a laboratory's specific needs for urine cultures be made to determine whether or not such rapid urine screening systems are appropriate.

An IMS/ATP Assay for the Detection ofMycobacterium tuberculosisin Urine

“…In contrast, organisms with a thicker cell wall, including the mycobacteria and Candida , exhibited increasing signal over time due to the additional time required to break down the cell walls to release ATP (Figure 2). The increase in signal is a distinguishing feature of mycobacteria and Candida that could allow differentiation from other common organisms associated with bacteriuria, namely, E. coli and mixed Gram-positive cocci [26]. It was also routinely observed that MTB had a modest increase in signal relative to other mycobacteria.…”

“…This is much higher than the approximately 20% sensitivity typical of sputum smear microscopy in HIV-positive patients with suspected TB [26] and is on a par with alternative diagnostic tests like the LAM ELISA, which has a reported sensitivity of 67–85% in HIV-positive patients [5]. All 19 flagged samples exhibited an increase in S : N for at least one time point after T1, and all yielded an average S : N/T1 of 0.98 or greater.…”

“…Second, C. albicans is not as commonly isolated from urine specimens as other organisms, so it is less likely to pose a problem with real-world samples. Yeasts comprised only 4 of 178 samples (0.02%) in one study of microorganisms isolated from 400 urine specimens [26]. …”

“…Nontarget microorganisms included common urine isolates [26], other mycobacteria, and Candida because of their morphological similarities to MTB. These strains were either ATCC strains or obtained from the University of South Florida Advanced Biosensors Laboratory (ABL) collection and included Mycobacterium smegmatis ABL 539, Mycobacterium avium ATCC 25921, Mycobacterium intracellulare ATCC 13950, Mycobacterium gordonae ATCC 14470, Rhodococcus rhodochrous ABL 538, Candida albicans ABL 537, Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis ATCC 12228, Staphylococcus simulans ATCC 11631, Enterococcus faecalis ATCC 19433, Escherichia coli K12 ABL 552, Pseudomonas aeruginosa ATCC 15442, and Klebsiella pneumoniae ATCC 29019.…”

“…IMS also enables specific target capture and decreases particulate interference in detection assays [23, 24]. ATP bioluminescence assays have demonstrated utility in bacteriuria screening [25, 26], quality control of BCG vaccines [27], and MTB antibiotic susceptibility testing [28]. Combining immunocapture with an ATP-based cell viability assay can provide rapid, specific, semiquantitative detection of live cells [29–31].…”