Identification of bacterial urinary tract pathogens from urine samples using conventional methods and matrix-assisted laser desorption ionization-time of flight mass spectrometry

Supreet Kanwar, Loveena Oberoi, Kanwardeep Singh, Bimla Devi


Background: Early diagnosis of urinary tract infections (UTIs) is essential to avoid inadequate or unnecessary empirical antibiotic therapy. In this study, we evaluate the coincidence rate between conventional method for the diagnosis of UTIs (plate cultures and identification based on biochemical characteristics) and a fast method based on Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS). In recent years, proteomic techniques have achieved a relevant role in the identification of microorganisms in the field of clinical microbiology. MALDI-TOF MS has been suggested as a fast and reliable method for bacterial identification.

Methods: Around 50 midstream urine samples submitted to Microbiology laboratory for Gram staining and bacterial culture were analyzed. Samples were microscopically tested, characterized, and identified using different media such as blood agar and Mac Conkey agar and by applying suitable biochemical tests. Urine specimens showing a significant bacteriuria on culture and single morphological type by Gram staining were then processed by MALDI-TOF MS.

Results: Of 50 specimens, colony growth was observed in 43(86%) specimens, and 38(88.3%) specimens had growth of single-colony morphological type in culture. 32(84.2%) of them had colony counts of >105 colony forming units (CFUs)/ml. 7(14%) samples were negative in culture, and all of them were also negative by MALDI-TOF MS. Microorganism identifications in this group were coincident at the species level in 28(87.5%) specimens. The most frequent microorganism identified was Escherichia coli, followed by Klebsiella species and Acinetobacter baumanii. MALDI-TOF MS identified Providencia stuartii in 3 samples and Pseudomonas putida in 1 of them; which were not in accordance with the conventional method used for identification.

Conclusions: Present study results show that MALDI-TOF MS allows bacterial identification from infected urine in a short time, with high accuracy, and especially when uncommon uropathogens are involved.


Gram negative bacilli, Gram positive cocci, MALDI-TOF MS, Urinary tract infections

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