Comparison of five methods for detection of carbapenemases in Enterobacterales with proposal of a new algorithm.

OBJECTIVES: The aim of this study was to evaluate the performance of five different carbapenemase tests and to develop an algorithm which will permit the detection of most common and rare carbapenemases in routine microbiology laboratories. METHODS: The immunochromatographic tests CARBA-5 (NG), RESIST-4 O.K.N.V. (Coris), the colorimetric ß-CARBA (BioRad), a newly developed carbapenem-inactivation method (CIM) supplemented with zinc (zCIM), and the Xpert Carba-R (Cepheid) were challenged with a collection of 189 molecularly characterized Enterobacterales isolates, including 146 carbapenemase producers (CPE): VIM (n = 48), OXA-48-like (n = 40), NDM (n = 29), KPC (n = 13), IMI (n = 9), IMP (n = 9), OXA-58 (n = 2), and GES (n = 2). RESULTS: The overall sensitivity/specificity values for the five carbapenemase detection tests were 84.2% (CI 77.6-89.2%)/100% (CI 91.8-100%) for RESIST-4, 88.2% (CI 82.1-92.4%)/100% (CI 91.8-100%) for CARBA-5, 88.2% (CI 82.1-92.4%)/100% (CI 91.8-100%) for Xpert Carba-R, 73.7% (CI 66.2-80.0%)/100% (CI 93.4-99.0%) for ß-CARBA, and 97.4% (CI 87.9-99.6%)/97.7% (CI 87.9-99.6%) for zCIM. The four common carbapenemases (KPC, OXA-48-like, NDM, and VIM) were detected with ≥97.6% sensitivity by all tests except for ß-CARBA (76.6% (CI 68.4-83.2%)). IMI and GES were only detected by zCIM (sensitivity 90.9% (CI 62.3-98.4%)). Based on these results a new algorithm was developed, consisting of an immunochromatographic assay as the first test followed by zCIM, which allows detection of 99.3% of all carbapenemases assessed. CONCLUSIONS: Except for ß-CARBA, all methods showed excellent sensitivity/specificity for the detection of the four most frequent carbapenemases. With the new algorithm, rare variants can also be detected. It is rapid, simple, and inexpensive and can be performed in any microbiology laboratory, as no PCR equipment is required.

Changes in Clostridium (Clostridioides) difficile PCR-Ribotype Distribution and Antimicrobial Resistance in a German Tertiary Care Hospital Over the Last 10 Years.

Clostridium (Clostridioides) difficile ribotype 027 (RT027) was detected in Germany for the first time in 2007 during an outbreak in the region of Trier, Rhineland-Palatinate and is today the most prevalent ribotype (RT) in Europe. We aimed to determine the changes in RT distribution and corresponding antimicrobial resistance in clinical C. difficile isolates between two time points (2007 and 2017) in one tertiary care hospital in Germany. C. difficile isolates recovered in 2007 and in 2017 (80 isolates per year, respectively) from patients at a Tertiary Care University Hospital in North-Rhine Westphalia were analyzed. Isolates were characterized by ribotyping and susceptibility testing using gradient tests (metronidazole, vancomycin) and the disk diffusion method (moxifloxacin). Between 2007 and 2017, a clear switch from RT001 [18.75% (n = 15) in 2007 versus 3.75% (n = 3) in 2017 P = 0.003] to RT027 [0% in 2007 versus 21.25% (n = 17) in 2017] was evident. While minimal inhibitory concentrations (MICs) of vancomycin were stable, a significant metronidazole MIC creep was determined (MIC50 = 0.047 in 2007 versus MIC50 = 0.094 in 2017, P < 0.0001 using the Man-Whitney test). We detected one metronidazole-resistant isolate (0.6%). Interestingly, in total we encountered more isolates resistant to moxifloxacin in 2007 (42 (52.25%) than in 2017 [(30 (37.5%), P = 0.06)]). We could demonstrate that RT027 replaced RT001 in the last 10 years in our hospital. Furthermore, our data show a metronidazole MIC creep in C. difficile isolates over the last 10 years and an unexpected decrease of isolates resistant to moxifloxacin.

Evaluation of the Use of Rectal Swabs for Laboratory Diagnosis of Clostridium difficile Infection.

For the diagnosis of Clostridium difficile infection (CDI), microbiological testing is almost always accomplished through the analysis of stool specimens. We evaluated the performances of rectal swabs with liquid transport medium (FS) and nylon flocked dry swabs for the detection of C. difficile Additionally, the impact on the diagnostic yield of storing swabs at -80°C for up to 3 months was evaluated. Sixty clinical stool samples positive for C. difficile by PCR were used for simulating rectal swabbing. FS and dry swabs were dipped into the stool and tested by PCR directly after swabbing at 1 and 3 months after storage at -80°C. Stool and the liquid medium of FS were additionally tested by a combination of glutamate dehydrogenase antigen (GDH) testing and toxin A/B enzyme immunoassay (EIA), as well as by toxigenic culture (TC). Using dry swabs, the PCR-based detection rate of C. difficile was equal to the rate using stool samples (30/30 [100%]), whereas the detection rate in FS was significantly lower (25/30 [83.2%]; P = 0.019). The sensitivities of FS for detecting C. difficile by PCR, TC, GDH testing, and toxin A/B EIA were 83.3%, 85.7%, 88%, and 68.9%, respectively. Storage of swabs at -80°C had no impact on the detection rate. FS cannot replace stool samples in the two-step laboratory diagnosis of CDI, as the sensitivities were too low, probably due to diluting effects of the fecal sample in the liquid medium. For simple PCR-based detection of C. difficile, dry swabs proved to be a suitable alternative to the use of stool samples.

Pop-off system for the high flow IMV reservoir bag.

A pop-off valve system for use with intermittent mandatory ventilation that employs high flow and a reservoir bag is described. It ensures constancy of the mechanical tidal volume regardless of the flow rate of fresh gases into the reservoir bag of the spontaneous breathing circuit.