Identification and susceptibility profile of microorganisms isolated directly from urine in a cross-sectional study...

This study evaluates the efficacy of matrix-assisted laser desorption ionization-time of flight technology and the Phoenix™ M50 system for bacterial identification and antimicrobial susceptibility testing from bacterial concentrate obtained from urine samples, reducing diagnostic time to 24 hours compared to the traditional 72 hours in a public hospital in Antofagasta, Chile.

Through differential centrifugation, a bacterial concentrate is obtained directly from urine, allowing the preparation of a McFarland standard for identification and susceptibility studies. We compared the identification and minimal inhibitory concentration results obtained from the bacterial concentrate with those obtained from the strain isolated in culture.

380 samples were analyzed after exclusions. Direct identification showed 93.4% sensitivity and 73.8% specificity, with moderate agreement (κ=0.604) versus culture. had 98.5% concordance. For antimicrobial susceptibility test, Phoenix M50 performed well with , meeting Cumitech 31A standards for 13 out of 19 antibiotics. In contrast, only 8 of 19 antibiotics met the criteria for .

The antimicrobial susceptibility method varies depending on the species-antibiotic combination; therefore, specific studies for each species are crucial. Despite these challenges, the direct method offers significant advantages in diagnostic speed and emphasize its potential for improving clinical decision-making, though further validation and protocol refinement are needed, particularly for Gram-positive pathogens.