Fast antibiotic susceptibility testing of urine microflora using a microbiological analyzer based on coherent fluctuation nephelometry

Background: Traditional culture-based microbiological methods remain the most used for defining the etiology of urinary tract infections and antibiotic susceptibility testing (AST) of isolated uropathogens. They are time-consuming and lead to delays of several days when obtaining the final results of microbiological tests.

Objectives: In this study, we validate the possibility of using a microbiological CFN analyzer combined with MALDI-TOF mass spectrometry (MS) for fast conclusive urine testing (1 day) without obtaining pure cultures.

Materials and methods: The study included three stages: detection of urine microflora growth using the CFN analyzer to separate positive and negative samples within 2-4 h; fast MS identification of positive samples without isolating uropathogens; fast AST using CFN analyzer within 3-6 h. In parallel, all urine samples were tested by traditional culture-based microbiological methods.

Result: In total, 194 urine samples were tested, and 22 urine cultures were identified by MS, among them, 20 monocultures with bacterial counts ≥ 10⁵ and 2 mixed cultures. The AST of these 22 urine cultures and additional 88 pure clinical cultures was performed using eight antibiotics. Overall, 276 tests were performed. The results of AST obtained using the CFN analyzer and traditional methods were in good agreement (98.2%). Although two mixed cultures were falsely identified as monocultures, their susceptibility determined by the CFN analyzer was correct.

Conclusions: The CFN analyzer is promising and effective for fast AST. Combined with MS identification, it allows to perform full urine analysis in 1 day without the lengthy isolation of pure cultures.