Comparative performance study of six commercial molecular assays for rapid detection of toxigenic Clostridium difficile.

OBJECTIVES: Rapid and accurate detection of Clostridium difficile in stool affects patient treatment and containment efforts. Detection of C. difficile toxin genes using nucleic acid amplification techniques (NAAT) is part of a multistep algorithm. Our objective was to directly compare the diagnostic accuracy and applicability of six commercial C. difficile NAAT. METHODS: Two hundred ten specimens were analysed in parallel by six commercial NAAT. Toxigenic culture was used as a reference method. RESULTS: We analysed 98 positive and 112 negative samples. The Xpert C. difficile had 99% sensitivity (95% confidence interval (CI) 94.45-99.97), followed by Simplexa C. difficile Universal Direct 95% (95% CI 88.49-98.32), Illumigene C. difficile, and Quidel AmpliVue C. difficile, both 93% (95% CI 85.84-97.08), and BDmax Cdiff and GenomEra C. difficile, both 92% (95% CI 84.55-96.41). All assays had very high specificity (>99%). Invalid results requiring retesting were the highest in GenomEra (6.7%; 14/210) and BDmax (4.3%; 9/210), followed by AmpliVue (1.4%; 3/210) and Xpert (0.96%; 2/210). No retesting was required with Simplexa and Illumigene. The turnaround time was the shortest for the Illumigene and Xpert and the longest for BDmax, mostly due to the different reaction times of assays. Total hands-on time was comparable for all six assays. CONCLUSIONS: All assays had high sensitivity and specificity. The differences in turnaround time, repeat testing rates and platform characteristics could help laboratories decide which assay would integrate better in their setting and to better select a molecular platform for C. difficile detection.

A multicenter study of the clonal structure and resistance mechanism of KPC-producing Escherichia coli isolates in Israel.

Little is known about the molecular epidemiology of Klebsiella pneumoniae carbapenemase-producing Escherichia coli (KPCEC). We aimed to describe the clonal structure and resistance mechanisms of KPCEC in a multicenter study. The study included 88 isolates from four medical centres in Israel: Tel Aviv Medical Center (n = 17), Laniado Medical Center (n = 12), Sha'are-Zedek Medical Center (n = 38), and Rambam Medical Center (n = 21). Twelve (14%) KPCEC were from clinical sites and 86% from surveillance cultures. The clonal structure was studied by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) and was highly diverse, with 79 and 45 different PFGE types and STs, respectively. The most common clones were ST-131 and ST-410, identified in 21 isolates (23%). Dominant clonal complexes (CCs) were CC131 (n = 16), CC410 (n = 14), CC10 (n = 17), and CC-69 (n = 6). The blaKPC-2 and blaKPC-3 genes were identified in 68 and 20 isolates, respectively. All isolates were non-susceptible to ertapenem; 16 (18%) and 35 (40%) isolates were susceptible (minimal inhibitory concentration ≤1 mg/L) to imipenem and meropenem, respectively. Isolates were susceptible to colistin, amikacin, ciprofloxacin, gentamicin, and trimethoprim-sulfamethoxazole in 100%, 87%, 28%, 27%, and 21% of the cases, respectively. blaKPC-Harbouring plasmids from Tel Aviv Medical Center as well as from six CC-131 isolates from the other centres were studied by Inc and pMLST typing. Sixteen of the 20 blaKPC2-harbouring plasmids were of identical type, IncN-pMLST ST-15. In conclusion, the clonal structure of KPCEC in Israel is characterized by the predominance of known international extended-spectrum ß-lactamase-producing clones and by high intra- and inter-institutional diversity. This suggests that in Israel, clonal spread does not play a major role in the dissemination of KPCEC.