Standardization of isothermal microcalorimetry in urinary tract infection detection by using artificial urine.

PURPOSE: Isothermal microcalorimetry (IMC) has recently been reported as a new method to rapidly detect urinary tract pathogens (UTP). However, further application of microcalorimetry in the clinical setting requires a standardized procedure. An important step toward such standardization is to use a reproducible growth medium. In this study, we investigated the potential of artificial urine in combination with microcalorimetry for detection of common UTP. METHODS: A microcalorimeter equipped with 48 channels was used. Detection was accomplished, and growth was monitored for four bacterial strains in artificial urine at 37 °C by measuring metabolic heat flow (µW = µJ/s) as a function of time. The strains were Escherichia coli, Proteus mirabilis, Enterococcus faecalis, and Staphylococcus aureus. RESULT: Bacterial growth was detected after 3-32 h with decreasing inoculums down to 1 CFU. The gram-negative strains grew and were detected faster than their gram-positive counterparts. The growth rates the different strains were 0.75 ± 0.11 for E. coli, 0.74 ± 0.10 for E. faecalis, 1.31 ± 0.04 for P. mirabilis, and 0.56 ± 0.20 for S. aureus. The shape of individual heat flow curves was characteristic for each species independent of its initial concentration. CONCLUSIONS: IMC allows rapid detection of UTP in artificial urine. Clearly, different heat flow patterns enable accurate pathogen differentiation. UTP detection after only 4 h is realistic. The rapid detection of UTP tested in standardized artificial urine proves the diagnostic potential of IMC and warrants further microcalorimetric studies in the clinical setting of urinary tract infections.