Rapid detection of bla_KPC carbapenemase genes by real-time PCR

Carbapenem resistance among Enterobacteriaceae is an emerging problem worldwide. Klebsiella pneumoniae carbapenemase (bla_KPC) enzymes are among the most common β-lactamases described. In this study, we report the development and validation of a real-time PCR (q-PCR) assay for the detection of bla_KPC genes using TaqMan chemistry. The q-PCR amplification of bla_KPC DNA was linear over 7 log dilutions (r² = 0.999; slope, 3.54), and the amplification efficiency was 91.6%. The q-PCR detection limit was 1 CFU, and there was no cross-reaction with DNA extracted from several multidrug-resistant bacteria. Perianal/rectal swabs (n = 187) collected in duplicate from 128 patients admitted to Sheba Medical Center surgical intensive care units were evaluated for the presence of carbapenem-resistant bacteria by culturing on MacConkey agar-pluscarbapenem disks and for bla_KPC genes by q-PCR. Carbapenem-resistant organisms, all K. pneumoniae, were isolated from 47 (25.1%) of the 187 samples collected, while bla_KPC genes were detected in 54 (28.9%) of the patient samples extracted by the NucliSENS easyMAG system. Of these, seven samples were positive for bla_KPC genes by q-PCR but negative for carbapenem resistance by culture, while all samples in which no carbapenem-resistant bacteria were detected by culture also tested negative by q-PCR. Thus, the sensitivity and specificity of the q-PCR assay after extraction by the NucliSENS easyMAG system were 100% and 95%, respectively. Similar values were obtained after DNA extraction by the Roche MagNA Pure LC instrument: 97.9% sensitivity and 96.4% specificity. Overall, the bla_KPC q-PCR assay appears to be highly sensitive and specific. The utilization of q-PCR will shorten the time to bla_KPC detection from 24 h to 4 h and will help in rapidly isolating colonized or infected patients and assigning them to cohorts.