# REL/DPA/AVI method: a novel approach for rapid detection of carbapenemase-producing Enterobacterales directly from positive blood cultures based on optical density

## TL;DR

A new rapid and low-cost method for detecting carbapenem-resistant bacteria in blood cultures is introduced, offering faster and more cost-effective results than current techniques.

## Contribution

The REL/DPA/AVI method is a novel, rapid, and cost-effective phenotypic test for early detection of carbapenemase-producing Enterobacterales in blood cultures.

## Key findings

- The REL/DPA/AVI method detected carbapenemases in 1.5 to 2 hours with high sensitivity for classes A, B, and A + B.
- The method is significantly more cost-effective than existing technologies, with a cost of less than $1 USD per test.
- Compared to traditional methods like mCIM/eCIM and APB-EDTA, the REL/DPA/AVI method showed comparable or higher sensitivity for most carbapenemase classes.

## Abstract

The high mortality rate associated with carbapenem-resistant Enterobacterales (CRE), particularly for bloodstream infections (BSI), underscores the urgent need for early identification and differentiation of its resistance mechanisms. In China, traditional phenotypic detection methods for carbapenemases, including the modified Carbapenem Inactivation Method (mCIM), EDTA Carbapenemase Inactivation Method (eCIM), and the carbapenemase inhibitor 3-aminophenylboronic acid (APB) and EDTA enhancement method (APB-EDTA method), are widely used; however, they are time consuming. The relebactam, dipicolinic acid, and avibactam sodium (REL/DPA/AVI) method is a novel phenotypic test for carbapenemase targeting to address these challenges. This method exploits the growth status differences of enzyme-producing bacteria under the combined action of imipenem and enzyme inhibitors (REL, DPA, and AVI) to identify Class A, B, and D carbapenemases at an early stage through optical density (OD) measurements. The REL/DPA/AVI method was optimized and evaluated using 213 contrived (seeded) blood cultures and compared to mCIM/eCIM and APB-EDTA methods. The REL/DPA/AVI method achieved results within 1.5 h (OD measurement) or 2 h (visual observation or OD measurement) from blood culture positivity. Sensitivities of detection of class A, B, D, and A + B carbapenemases at 1.5 h were 97.56% (40/41), 100% (82/82), 71.43% (5/7), and 100% (7/7), respectively. After 2 h, the sensitivity for detecting class D carbapenemases increased to 85.71% (6/7). Conversely, the sensitivities of mCIM/eCIM were 95.83% (46/48) and 97.56% (80/82) for serine β-lactamases and metallo-β-lactamases, respectively. However, the APB-EDTA method demonstrated a sensitivity of 95.1% (39/41), 87.8% (72/82), and 71.43% (5/7) for classes A, B, and A + B carbapenemases, respectively.

The relebactam, dipicolinic acid, and avibactam sodium (REL/DPA/AVI) method has demonstrated significant success in identifying and differentiating carbapenemase-producing Enterobacterales (CPE) from positive blood cultures, exhibiting superior performance compared with existing technologies. Although numerous advanced technologies such as mNGS, Filmarray, Verigene, and NG-Test CARBA 5 DetecTool have been developed for carbapenemase typing of CPE in positive blood cultures, our method is distinguished by a significant economic advantage, with a cost of less than $1 USD per test. This substantial cost-effectiveness underscores the immense potential for widespread clinical applications.