Abstract
Carbapenem-resistant Acinetobacter baumannii (CRAB) presents a serious therapeutic and infection control challenge. In this study, we investigated the epidemiological and molecular differences of CRAB and the threatening factors for contributing to increased CRAB infections at a hospital in western China. A total of 110 clinical isolates of A. baumannii, collected in a recent 2-year period, were tested for carbapenem antibiotic susceptibility, followed by a molecular analysis of carbapenemase genes. Genetic relatedness of the isolates was characterized by multilocus sequence typing. Sixty-seven of the 110 isolates (60.9%) were resistant to carbapenems, 80.60% (54/67) of which carried the blaOXA-23 gene. Most of these CRAB isolates (77.62%) were classified as clone complex 92 (CC92), and sequence type (ST) 92 was the most prevalent STs, followed by ST195, ST136, ST843, and ST75. One CRAB isolate of ST195 harbored plasmid pAB52 from a Chinese patient without travel history. This plasmid contains toxin–antitoxin elements related to adaptation for growth, which might have emerged as a common vehicle indirectly mediating the spread of OXA-23 in CRAB. Thus, CC92 A. baumannii carrying OXA-23 is a major drug-resistant strain spreading in China. Our findings indicate that rational application of antibiotics is indispensable for minimizing widespread of drug resistance.
Highlights
Acintobacter baumannii is an opportunistic Gram-negative pathogen, which has recently been successfully spreading worldwide nosocomial infections and causing outbreaks of hospitalacquired infections, primarily due to its prominent ability to acquire antibiotic resistance (Peleg et al, 2008; Kempf and Rolain, 2012)
The results were interpreted according to the CLSI guidelines (CLSI, 2014), i.e., Carbapenem-resistant Acinetobacter baumannii (CRAB) was defined as an A. baumannii isolate that was resistant to both imipenem and meropenem (i.e., ≥8 μg/ml as resistant), whereas carbapenem-susceptible A. baumannii (CSAB) possessed carbapenem Minimal Inhibitory Concentration (MIC) of ≤2 μg/ml and carbapenem-intermediate A. baumannii (CIAB) has MIC of 4 μg/ml)
Clinical characterization of 67 patients with CRAB indicated that compromised immunity increases the risk of A. baumannii infection
Summary
Acintobacter baumannii is an opportunistic Gram-negative pathogen, which has recently been successfully spreading worldwide nosocomial infections and causing outbreaks of hospitalacquired infections, primarily due to its prominent ability to acquire antibiotic resistance (Peleg et al, 2008; Kempf and Rolain, 2012). Class A, C, and D (OXA enzymes) of β-lactamases contain a catalytically active serine residue that cleaves the lactam ring of antibiotics (Bush et al, 1995; Tiwari and Moganty, 2014). Class B of β-lactamases is a metallo-enzyme that requires zinc for their catalytic activity, and has a completely different mechanism for enzyme activity (Tiwari and Moganty, 2013) Carbapenems, such as imipenem and meropenem, have an exceedingly broad spectrum of activity and are able to resist hydrolysis by most of the β-lactamases, including extended-spectrum and derepressed class C chromosomal AmpC β-lactamases (Bush et al, 1995). Liu et al (2015) reported the dissemination of MDR OXA-23-producing A. baumannii clones throughout multiple cities in China, but little is known about the molecular mechanisms of resistance to carbapenems in western China
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