Combination of matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) and UX2000 urine flow-cytometry for rapid detection and identification of urinary tract pathogens
Eur Urol Suppl 2014;13;e456 Print!
Bonkat G.1 , Müller G.1 , Berini A. 2 , Frei R.2 , Goldenberger D.2 , Regeniter A. 3 , Rieken M. 1 , Braissant O.1 , Gasser T.C.1 , Bachmann A. 1 ,
Egli A. 2
1 University
Hospital Basel, Dept. of Urology, Basel, Switzerland, 2 University Hospital Basel, Dept. of Clinical Microbiology Laboratory, Basel,
Switzerland, 3 University Hospital Basel, Dept. of Laboratory Medicine, Basel, Switzerland
INTRODUCTION & OBJECTIVES: Rapid and specific diagnosis of urinary tract infection (UTI) is central to early commencement of
effective empiric antimicrobial therapy. Conventional urine culture requires up to 72 hours from sample collection to the delivery of pathogen
identification. Urine flow-cytometry (UF) offers a fast method to determine the quantity of bacteria and leucocytes. MALDI-TOF, a novel
mass-spectrometry based technology, is able to identify bacterial species very rapidly. Combining these technologies may significantly
shorten the time to microbiological identification and initiation of adequate antibiotic treatment.
MATERIAL & METHODS: We compared UF and MALDI-TOF versus standard and automated culture methods. Urine samples were
centrifuged and washed to remove leucocytes and enrich bacteria in a rapid protocol followed by MALDI-TOF. Two clinical settings were
initially examined: (cohort I) analysis of randomly selected routine urinary specimens sent to the laboratory; (cohort II) culture positive urine
samples with equal or greater than 10e6 bacterial cells per mL urine to specify the assay performance.
RESULTS: Cohort I: UF identified in 11 of 32 urine samples significant bacterial loads (≥10e4/mL) and leucocytes (male ≥20/uL and female
≥40/uL), suggesting active infection. Only in 1/11 samples a single bacterial pathogen, Klebsiella pneumoniae, could be identified by both
culture and MALDI-TOF. In 3/11 samples no bacterial growth occurred, in 7/11 mixed culture or low bacterial load (≤10e5/mL) was present,
which yielded no identification by MALDI-TOF. Cohort II: 13/42 urine samples did not fulfill the UF inclusion criteria. In addition, 12/42 either
the bacterial load determined by culture was ≤10e5/mL or multiple microorganisms were present. Nevertheless, MALDI-TOF detected low
discriminatory peaks in 6 these 12 samples. Among the remaining 17 samples, in 10 the bacterial species could be successfully determined
(MALDI-TOF scores ≥2.0), reflecting an almost 60% early identification success rate.
CONCLUSIONS: These preliminary results show that urine samples intended to be directly analyzed by MALDI-TOF mass spectrometry
should be pre-selected by UF. In urine samples with significant bacteria and leukocyte counts MALDI-TOF is able to rapidly identify the
causative pathogens. Although this method will need further improvement we believe that this approach will lead to targeted adjustment of
antibiotic treatment at early stages in the setting of UTI.