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 β-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 β-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 β-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 β-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.

Rapid detection of OXA-48-like, KPC, NDM, and VIM carbapenemases in Enterobacterales by a new multiplex immunochromatographic test

The rapid detection of carbapenemase-producing Gram-negative bacteria is indispensable to optimize treatment and avoid the further spread of these organisms. While phenotypic tests are time-consuming and PCR is expensive and not available in many routine laboratories, immunochromatographic tests (ICT) can provide rapid results at moderate cost. The aim of this study was to determine the performance of the new ICT RESIST-4 O.K.N.V. K-SeT (Coris BioConcept, Gembloux, Belgium) which can detect the four most prevalent carbapenemases: OXA-48-like, KPC, NDM, and VIM. Additionally, we analyzed the impact of different culture conditions on the sensitivity. The new ICT was challenged with 169 carbapenem-resistant isolates. Of these, 125 were carbapenemase producers: 43 OXA-48-like, 15 KPC, 29 NDM, and 43 VIM. The ICT correctly detected 129 of the 130 carbapenemases resulting in a sensitivity of 99.2% and specificity of 100% when tested from Mueller-Hinton agar (MHA). The sensitivity of the assay increased to 100% when performed from zinc-supplemented MHA and sheep blood agar (SBA) or when the inoculum was harvested from the inhibition zone of an ertapenem disk. All carbapenemase-negative carbapenem-resistant bacteria tested negative and no cross-reaction was observed. The new ICT is an excellent test for rapid diagnostic of carbapenemase-producing Gram-negatives in the routine laboratory. It is easy to handle and provides rapid results with a high sensitivity. For best results, we recommend to obtain the inoculum from a medium with sufficient zinc or from the inhibition zone of an ertapenem disk.

Inherited variation in vitamin D genes is associated with predisposition to autoimmune disease type 1 diabetes

OBJECTIVE

Vitamin D deficiency (25-hydroxyvitamin D [25(OH)D] <50 nmol/L) is commonly reported in both children and adults worldwide, and growing evidence indicates that vitamin D deficiency is associated with many extraskeletal chronic disorders, including the autoimmune diseases type 1 diabetes and multiple sclerosis.

RESEARCH DESIGN AND METHODS

We measured 25(OH)D concentrations in 720 case and 2,610 control plasma samples and genotyped single nucleotide polymorphisms from seven vitamin D metabolism genes in 8,517 case, 10,438 control, and 1,933 family samples. We tested genetic variants influencing 25(OH)D metabolism for an association with both circulating 25(OH)D concentrations and disease status.

RESULTS

Type 1 diabetic patients have lower circulating levels of 25(OH)D than similarly aged subjects from the British population. Only 4.3 and 18.6% of type 1 diabetic patients reached optimal levels (≥75 nmol/L) of 25(OH)D for bone health in the winter and summer, respectively. We replicated the associations of four vitamin D metabolism genes (GC, DHCR7, CYP2R1, and CYP24A1) with 25(OH)D in control subjects. In addition to the previously reported association between type 1 diabetes and CYP27B1 (P = 1.4 × 10(-4)), we obtained consistent evidence of type 1 diabetes being associated with DHCR7 (P = 1.2 × 10(-3)) and CYP2R1 (P = 3.0 × 10(-3)).

CONCLUSIONS

Circulating levels of 25(OH)D in children and adolescents with type 1 diabetes vary seasonally and are under the same genetic control as in the general population but are much lower. Three key 25(OH)D metabolism genes show consistent evidence of association with type 1 diabetes risk, indicating a genetic etiological role for vitamin D deficiency in type 1 diabetes.