Rapid urine preparation prior to identification of uropathogens by MALDI-TOF MS

Abstract

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-ToF MS) has been introduced in clinical routine microbiology laboratories. For the rapid diagnosis of urinary tract infections, culture-independent methods prior MALDI-mediated identification have been described. Here, we describe a comparison of three of these methods based on their performance of bacterial identification and their potential as a routine tool for microbiology labs : (i) differential centrifugation, (ii) urine filtration and (iii) a 5-h bacterial cultivation on solid culture media. For 19 urine samples, all methods were directly compared and correct bacterial species identification by MALDI was used as performance indicator. A higher percentage of correct MALDI identification was obtained after filtration (78.9 %) and the growth-based method (84.2 %) as compared to differential centrifugation (68.4 %). Additional testing of 76 mono-microbial specimens (bacteriuria > 10(5) CFU/mL) confirmed the good performance of short growth with a 90.8 % correct MALDI score, with a potentially better fit to the routine workflow of microbiology labs.

New and developing diagnostic technologies for urinary tract infections

“…Currently, these technologies are performed in a clinical laboratory and require initial isolation of bacteria or considerable sample processing to isolate the bacterial cells from the urine matrix before analysis 62,63 . Repurposing these technologies for diagnosing UTI directly from urine is possible and could result in substantially improved efficiency and clinical outcome over current culture methods.…”

“…Several groups have explored direct analysis of urine samples using MALDI–TOF to decrease the time needed for pathogen identification 48,50,62,66 . For direct analysis of urine, initial sample preparation steps are necessary to remove cellular debris, leukocytes, and mucus, and to collect bacteria.…”

“…71)) might present a considerable obstacle for adoption in smaller clinics limiting use of this platform to high-volume laboratories. Additionally, whether MALDI–TOF can meet the demands of UTI diagnostics is unclear, given the need for upstream screening to improve the diagnostic yield of positive samples and the need for initial sample processing, although efforts are underway to simplify sample preparation 62 . In its current iteration, analysis of MALDI–TOF results is confounded by poly-microbial samples.…”

Direct Detection and Identification of Bacterial Pathogens from Urine with Optimized Specimen Processing and Enhanced Testing Algorithm

“…Zboromyrska et al used 10 ml of urine for MALDI-TOF MS and obtained higher score values of direct identification (16). In order to improve the LOD, Sánchez-Juanes et al added a pretreatment with SDS to enhance cell lysis and the release of microorganisms, and Veron et al compared different methods, concluding that previous short-culture and dual-filtration methods provided the best results (18,19). We suggest a starting volume of 15 ml, as conical tubes and centrifuges of this size are routinely available in clinical bacteriology laboratories.…”

Prospective Evaluation of Light Scatter Technology Paired with Matrix-Assisted Laser Desorption Ionization – Time of Flight Mass Spectrometry for Rapid Diagnosis of Urinary Tract Infections

“…Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has recently been applied as a direct urine-screening tool. Several studies have evaluated this approach using a variety of centrifugation and filtration techniques to separate bacteria from substances that might interfere with MALDI-TOF MS (i.e., white blood cells) (9)(10)(11)(12)(13)(14)(15)(16)(17). Unfortunately, these protocols have shown limited promise.…”