¹H-nuclear magnetic resonance spectroscopy for identifying and quantifying common uropathogens: A metabolic approach to the urinary tract infection

OBJECTIVE To address the shortcomings of urine culture for the diagnosis of urinary tract infection (UTI), we used ¹H-nuclear magnetic resonance (NMR) spectroscopy for identifying and quantifying Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumonia and Proteus mirabilis. PATIENTS, SUBJECTS AND METHODS Urine samples from patients with suspected UTI (617), healthy volunteers (50) and commercially available standard strains of E. coli, K. pneumonia, P. aeruginosa, Enterobacter, Acinobacter, Pr. mirabilis, Citrobacter frundii, Streptococcus saprophyticus and Enterococcus faecalis were assessed between 2003 and 2006. ¹H-NMR spectra were recorded on a 400 MHz spectrophotometer; to quantify the bacteria we estimated the areas under the spectral peaks of the specific metabolic product compared with the known concentration of trimethyl silyl propionic acid. All urine specimens were cultured in addition to an assessment by NMR spectroscopy. RESULTS Preliminary urinary spectroscopy of the unprocessed samples showed peaks of nonspecific metabolites such as succinate, acetate, lactate and ethanol, indicating infected samples. Based on the results from processed samples, 93% (240/256) of E. coli, 92% (101/110) of K. pneumoniae, 93% (56/60) of P. aeruginosa and eight of 10 Pr. mirabilis could be diagnosed with NMR (numerator) and urine culture (denominator). The remaining samples were sterile and/or had a bacterial population of <10³ colony-forming units (CFU)/mL. The NMR method diagnosed bacterial densities of >10³ CFU. CONCLUSIONS The identification of the common uropathogens E. coli, K. pneumoniae, P. aeruginosa and Pr. mirabilis by NMR spectroscopy has a shorter reporting time and can be used to differentiate between infected, contaminated and sterile specimens.