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There is an urgent need for accurate and fast diagnostic tests to identify carbapenemase-producing bacteria. Here, we evaluated a colorimetric imipenem hydrolysis test, called the CARBA PAcE test, to detect carbapenemase-producing Gram-negative bacteria (GNB). We tested a collection of 270 GNB isolates with a characterized carbapenemase content. Our testing set included 205 carbapenemase-producing, carbapenemase-resistant Enterobacterales ( CP CRE ) with 40 Klebsiella pneumoniae carbapenemase (KPC), 49 New Delhi metallo beta lactamase (NDM), 49 OXA-48-like, 15 Verona integron-mediated metallo-β-lactamase (VIM), three IMP, 43 IMI, six isolates producing more than one carbapenemase, and 65 non-carbapenemase-producing Enterobacterales (20 ESBL producers, 35 non-carbapenemase-producing, carbapenem-resistant [non-CP CRE], and 10 carbapenem-susceptible Enterobacterales [non-CP, non-CSE, third-generation cephalosporin and carbapenem susceptible]). We compared the performances of the CARBA PAcE test, the qualitative colorimetric β-CARBA test, and the modified CarbaNP test to a gold standard of carbapenemase gene detection by PCR. Specificities of all tests were high: 95.4% (62/65) for CARBA PAcE test, 98.5% (64/65) for β-CARBA test, and 100% (65/65) for the modified CarbaNP test. Sensitivity varied by carbapenemase: all three tests had a sensitivity of 100% for NDM, VIM, and IMP and 97.5% for KPC. Sensitivity to detect IMI was 0% for the CARBA PAcE and β-CARBA tests and 11.6% for the modified CarbaNP test. Sensitivity to detect OXA-48-like was 89.7% for the CARBA PAcE test, 87.7% for the β-CARBA test, and 14.2% for the modified CarbaNP test. Reading the results of the CARBA PAcE assay was difficult. The CARBA PAcE assay is highly sensitive for detecting NDM, VIM, IMP, and KPC, but slightly less sensitive for OXA-48-like. It does not detect IMI. It is highly specific, and its overall diagnostic accuracy is similar to that of β-CARBA. Its operational advantages are rapid turnaround time, ease of use, and long shelf life, but reading of results is subjective.IMPORTANCEWe evaluated the ability of the CARBA PAcE test to detect carbapenemases in 274 Gram-negative isolates with a known carbapenemase content. Specificity was high for all carbapenemases tested (96.9%). Sensitivity was high for KPC, NDM, VIM, and IMP (97.5-100%); but lower for OXA-48-like (89.7%). Activity of IMI could not be detected. Taken together, our results indicate that CARBA PAcE is a useful alternative in regions where NDM and KPC are predominant. The limitations of the test are difficulty in reading results and incompatibility with mSuperCARBA.

Timely detection of carbapenem-resistant Acinetobacter baumannii (CRAB) carriers is essential to direct infection control measures. In this work, we aimed to develop a practical protocol to detect CRAB from screening samples. To choose a selective medium that detects CRAB with high sensitivity and specificity, 111 A . baumannii clinical isolates were inoculated on three types of agar: mSuperCARBA (SC), CHROMagar Acinetobacter (CaA), and modified CHROMagar Acinetobacter (mCaA) containing 4.5 mg/mL meropenem. SC was non-selective, CaA was the most sensitive (100%), but only moderately specific (72%), and mCaA was highly specific (97%) and sensitive (98%). Confirmation of the carbapenem-resistant phenotype using PCR-based detection of bla OXA-23 , bla OXA-24 , and bla OXA-58 genes was specific but not sensitive, detecting only 58% of CRAB isolates. Identification of A. baumannii using either gyrB or bla OXA-51 PCR was excellent. Next, we used the same methodology in routine screening for CRAB carriage. mCaA had the best yield, with high sensitivity but moderate specificity to differentiate between CRAB and other carbapenem-resistant organisms. Skin sampling using sponges and 6 hour enrichment was highly sensitive (98%), while other body sites had poor sensitivity (27%- 41%). Shorter incubation had slightly lower yield, and longer incubation did not improve the detection. Performing PCR for bla OXA-51 and gyrB on colonies growing on modified mCaA differentiated between CRAB and other species with high accuracy (98% and 99%, respectively). Based on our results, we present a procedure for easy and reliable detection of CRAB carriage using skin sampling, short enrichment, selection on mCaA, and PCR-based identification., Importance: Carbapenem-resistant Acinetobacter baumannii (CRAB) is a substantial cause of nosocomial infections, classified among the most significant multidrug-resistant pathogens by the World Health Organization and by the US Centers for Disease Control. Limiting the spread of CRAB is an important goal of infection control, but laboratory methods for identification of CRAB carriers are not standardized. In this work, we compared different selective agar plates, tested the efficiency of A. baumannii identification by PCR for species-specific genes, and used PCR-based detection of common resistance genes to confirm the carbapenem-resistant phenotype. During a prospective study, we also determined the optimal sample enrichment time. Based on our results, we propose a simple and efficient protocol for the detection of CRAB carriage using skin sampling, short enrichment, selection on appropriate agar plates, and PCR-based identification, resulting in a turn-around time of 24 hours., Competing Interests: The authors declare no conflict of interest.

V ibrio c holerae c arbapenemase (VCC-1) is a chromosomal encoded class A carbapenemase thus far reported in environmental Vibrio cholerae isolates. Here, we report the first isolation of a bla VCC-1 -carrying Aeromonas caviae from a clinical sample in Israel. The isolate was resistant to all β-lactam agents, including carbapenems. The bla VCC-1 was located on a large plasmid. GC content suggests that the origin of the bla VCC-1 gene is neither Aeromonas nor Vibrio spp. but an unknown progenitor., Competing Interests: The authors declare no conflict of interest.