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Am J Clin Pathol. 2014 Feb;141(2):204-12. doi: 10.1309/AJCPQYW3B6JLKILC.

Diafiltration MALDI-TOF mass spectrometry method for culture-independent detection and identification of pathogens directly from urine specimens.

Author information

1
Dept of Pathology and Laboratory Medicine, St Paul's Hospital, 1081 Burrard St, Vancouver, BC V6Z 1Y6, Canada; mdmrco@mail.ubc.ca.

Abstract

OBJECTIVES:

With the aim of rapid, culture-independent identification of microorganisms directly from urine specimens, we developed a diafiltration matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method.

METHODS:

In this procedure, urine specimens are desalted, fractionated, and concentrated prior to MS analysis. The analytic performance characteristics of the diafiltration method were assessed in a prospective trial whereby 100 fresh urine specimens were processed using diafiltration MALDI-TOF MS. Concomitant with this, conventional culture was performed with results blinded to the MS operator.

RESULTS:

The diafiltration method correctly identified urine specimens positive for uropathogens (Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis) and correctly classified all specimens negative for clinically relevant bacteriuria, including a subset of contaminated urine specimens and a subset with growth of clinically insignificant flora. The sensitivity and specificity of the assay were 67% and 100%, respectively. The detection limit of this method was 10(5) to 10(6) colony-forming units/mL.

CONCLUSIONS:

Using the diafiltration method, we were able to improve the turnaround time for microorganism identification from 24 to 48 hours (for conventional culture) to 2 to 3 hours. Although methodological refinements are under way to further improve the clinical sensitivity and turnaround time, the 100% positive predictive value of this method suggests that it could be used to guide the selection of antimicrobial agents.

KEYWORDS:

Direct detection; MALDI-TOF; Mass spectrometry; Urinary tract infection; Urine

PMID:
24436267
DOI:
10.1309/AJCPQYW3B6JLKILC
[Indexed for MEDLINE]

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