Quantitative multiplex polymerase chain reaction in copies ml–1 linearly correlates with standard urine culture in colonies ml−1 for urinary tract infection (UTI) pathogens

Abstract

Standard urine culture (SUC) is the current standard method for confirmation of a urinary tract infection (UTI). SUC identifies microorganisms in urine samples and semi-quantifies these as colony-forming units (CFUs) ml−1. In contrast, quantitative multiplex polymerase chain reaction (q-MPCR) is a culture-independent assay in which the microbes are quantified by targeting genomic sequences and reported as cells ml−1, calculated from copies ml−1. Using serial dilutions within the 104–105 cells ml−1 range, the usual reporting range of SUC, this study compared the quantification results based on SUC and q-MPCR for four uropathogens with the control hemocytometer counts. The results revealed a linear relationship and a 1:1 correlation between the q-MPCR and SUC results. Additional q-MPCR quantification of 36 uropathogenic non-fastidious and fastidious bacteria and yeast indicated a reproducible linear correlation in a 1:1 manner with the control counts over a range of cell densities (103–106 cells ml−1). The results confirm that the quantifications by q-MPCR in cells ml−1 and by SUC in CFUs ml−1 are comparable and answer to the lingering question of how the results of these two methods correlate. Moreover, q-MPCR provided accurate quantification of various microorganisms over wider cell density ranges without the time required for microbial growth.