Background: Carbapenem-resistant Acinetobacter baumannii (CRAB) are an urgent public health threat because they cause healthcare-associated infections that are difficult to treat and can spread in healthcare environments. Acinetobacter spp may develop resistance to carbapenems through various mechanisms, including decreased permeability, overexpression of efflux pumps, and production of carbapenemases. Carbapenemases found in CRAB commonly belong to the group of carbapenem-hydrolyzing class D β-lactamases, which can be either intrinsic or acquired. The most clinically relevant class D enzymes are the OXA-23-like, OXA-24/40–like, and OXA-58–like because they are commonly plasmid mediated and thereby have the potential for rapid dissemination. We describe the molecular epidemiology of CRAB in the United States using a convenience sample of isolates collected from reference submissions, an isolate-based surveillance system, and the Antibiotic Resistance Laboratory Network (ARLN). Methods: Beginning in August 2017, 7 public health laboratories in the ARLN began testing CRAB isolates submitted by participating sentinel clinical laboratories across their region. Carbapenem-resistant isolates were identified by resistance to imipenem, meropenem, or doripenem. Testing included molecular detection of 4 targeted carbapenemase genes: blaKPC, blaNDM, blaVIM, and blaIMP. Participating labs reported testing results to CDC at least monthly. A separate collection of isolates from CDC reference and surveillance activities between 2013 and 2015 underwent whole-genome sequencing (WGS) to evaluate the presence of acquired carbapenemase genes, including class D OXA-variants. Results: From August 2017 through July 2019, the ARLN tested 2,368 CRAB isolates across 44 states. Only 12 (0.5%) of these harbored a bla- gene: blaKPC (n = 5), blaNDM (n = 5), blaIMP (n = 1), and blaVIM (n = 1). Of 95 reference and surveillance isolates sequenced, none harbored these targeted carbapenemases. However, 69 (73%) harbored at least 1 acquired class D OXA gene; OXA-23 was the most commonly acquired OXA variant (n = 46, 48.4%). Conclusions: Using a multipronged approach, our studies indicate that the presence of class D β-lactamases of the OXA type are common in CRAB among surveillance and reference samples that underwent WGS analysis. Other acquired carbapenemases appear to be rare. To prevent the spread of highly resistant CRAB, particularly those carrying the targeted, emerging carbapenemase genes, continued testing, and rapid infection control are necessary to improve patient safety and maintain situational awareness.

Funding: None

Disclosures: None