Descriptive analysis of targeted carbapenemase genes and antibiotic susceptibility profiles among carbapenem-resistant
Acinetobacter baumannii
tested in the Antimicrobial Resistance Laboratory Network—United States, 2017–2020
Authors: Sabour Sarah , Bantle Katie , Bhatnagar Amelia , Huang Jennifer Y. , Biggs Angela , Bodnar Janine , Dale Jennifer L. , Gleason Rachel , Klein Liore , Lasure Megan , Lee Rachel , Nazarian Elizabeth , Schneider Emily , Smith Lori , Snippes Vagnone Paula , Therrien Michelle , Tran Michael , Valley Ann , Wang Chun , Young Erin L. , Lutgring Joseph D. , Brown Allison C. 
Published: January 2024

ABSTRACT

Acinetobacter baumannii
is a Gram-negative bacillus that can cause severe and difficult-to-treat healthcare-associated infections.
A. baumannii
can harbor mobile genetic elements carrying genes that produce carbapenemase enzymes, further limiting therapeutic options for infections. In the United States, the Antimicrobial Resistance Laboratory Network (AR Lab Network) conducts sentinel surveillance of carbapenem-resistant
Acinetobacter baumannii
(CRAB). Participating clinical laboratories sent CRAB isolates to the AR Lab Network for characterization, including antimicrobial susceptibility testing and molecular detection of class A (
Klebsiella pneumoniae
carbapenemase), class B (Active-on-Imipenem, New Delhi metallo-β-lactamase, and Verona integron-encoded metallo-β-lactamase), and class D (Oxacillinase,
bla
OXA-23-like
,
bla
OXA-24/40-like
,
bla
OXA-48-like
, and
bla
OXA-58-like
) carbapenemase genes. During 2017‒2020, 6,026 CRAB isolates from 45 states were tested for targeted carbapenemase genes; 1% (64 of 5,481) of CRAB tested for targeted class A and class B genes were positive, but 83% (3,351 of 4,041) of CRAB tested for targeted class D genes were positive. The number of CRAB isolates carrying a class A or B gene increased from 2 of 312 (<1%) tested in 2017 to 26 of 1,708 (2%) tested in 2020. Eighty-three percent (2,355 of 2,846) of CRAB with at least one of the targeted carbapenemase genes and 54% (271 of 500) of CRAB without were categorized as extensively drug resistant; 95% (42 of 44) of isolates carrying more than one targeted gene had difficult-to-treat susceptibility profiles. CRAB isolates carrying targeted carbapenemase genes present an emerging public health threat in the United States, and their rapid detection is crucial to improving patient safety.

IMPORTANCE
The Centers for Disease Control and Prevention has classified CRAB as an urgent public health threat. In this paper, we used a collection of >6,000 contemporary clinical isolates to evaluate the phenotypic and genotypic properties of CRAB detected in the United States. We describe the frequency of specific carbapenemase genes detected, antimicrobial susceptibility profiles, and the distribution of CRAB isolates categorized as multidrug resistant, extensively drug-resistant, or difficult to treat. We further discuss the proportion of isolates showing susceptibility to Food and Drug Administration-approved agents. Of note, 84% of CRAB tested harbored at least one class A, B, or D carbapenemase genes targeted for detection and 83% of these carbapenemase gene-positive CRAB were categorized as extensively drug resistant. Fifty-four percent of CRAB isolates without any of these carbapenemase genes detected were still extensively drug-resistant, indicating that infections caused by CRAB are highly resistant and pose a significant risk to patient safety regardless of the presence of one of these carbapenemase genes.