Evaluation of matrix assisted laser desorption ionisation-time of flight mass spectrometry in direct identification of bacteriuria from urine samples.

Objective: The use of matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI) directly on urine can significantly improve turnaround time for diagnosing urinary tract infection (UTI). The present study was planned to compare the performance of MALDI directly on urine samples with conventional urine culture and evaluate an algorithm using a combination of significant pyuria and MALDI directly on urine samples as a screening method for diagnosing UTI.

Materials and Methods: A total of 1000 urine samples from patients with symptoms suggestive of UTIs were analysed. Urine microscopy, urine culture and MALDI were performed simultaneously on all the samples.

Results: MALDI correctly identified the microorganisms in 73.83% monomicrobial samples. In culture showing a mixed growth of two and more than three organisms, MALDI was able to identify one microorganism in 27.58% and 15.78% of samples, respectively. There were no peaks by MALDI in 93.53% of 464 sterile samples. The sequential algorithm using urine microscopy and MALDI could correctly identify UTI in 66.23% cases.

Conclusion: MALDI can be utilised to rule out bacteriuria in >93% of sterile urine samples. The combination of significant pyuria and direct MALDI as screening method to diagnose UTI (whether monomicrobial or polymicrobial) was not found to be superior than using direct MALDI on urine samples alone.