Abstract

INTRODUCTION This study evaluates the efficacy of matrix-assisted laser desorption ionization-time of flight technology and the PhoenixTM 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. METHODS 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. RESULTS 380 samples were analyzed after exclusions. Direct identification showed 93.4% sensitivity and 73.8% specificity, with moderate agreement (kappa=0.604) versus culture. E. coli had 98.5% concordance. For antimicrobial susceptibility test, Phoenix M50 performed well with E. coli, meeting Cumitech 31A standards for 13 out of 19 antibiotics. In contrast, only 8 of 19 antibiotics met the criteria for K. pneumoniae. CONCLUSIONS 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.