Although molecules with such properties are currently being tested (e.g. The development of a single molecule that would collectively inhibit all carbapenemases is a difficult task due to their different reaction mechanisms (zinc dependent metallo-beta-lactamases or serine reactive classes A and D). Therefore it should be considered for screening purposes after further clinical evaluation. Direct colorimetry of carbapenemase-induced imipenem decomposition required minimum reagents while exhibited high accuracy in detecting CPE. When applied on bacterial cell suspensions the assay could detect CPE with 96.7 % sensitivity and 100 % specificity with results being comparable to those obtained with the CARBA NP technique. The development of the yellow color was specific for carbapenemase containing enzyme preparations and the maximum intensity was achieved in acidic or un-buffered conditions in the presence of zinc. Optimal conditions were used for the analysis of cell suspensions and the assay was evaluated using 38 selected enterobacteria including 29 CPE as well as nine carbapenemase-negative strains overexpressing other β-lactamases. The effects of various buffers on reactions containing the potent carbapenemases NDM-1 and NMC-A were monitored at 405 nm. The reactions were studied by spectrophotometry in the visible spectrum using preparations of β-lactamases from the four molecular classes. Herein a low cost CPE detection method was developed that was based on the direct colorimetry of the yellow shift caused by the accumulation of diketopiperazines – products of the acid catalyzed imipenem oligomerization – induced by carbapenemase action on dense solutions of imipenem/cilastatin. Cost effective methodologies rapidly detecting carbapenemase producing enterobacteria (CPE) would facilitate such measures. In the absence of a molecule that would collectively inhibit both metallo-β-lactamases and serine reactive carbapenemases, containment of their genes’ spreading is the main weapon currently available for confronting carbepenem resistance in hospitals.
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