Co-Occurrence of blaOXA-23 in the Chromosome and Plasmid: Increased Fitness in Carbapenem-Resistant Acinetobacter baumannii.

Zhiren Wang,Hui Wang,Jiangang Zhang,Henan Li

doi:10.3390/antibiotics10101196

Zhiren Wang, Hui Wang + Show 2 more

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https://doi.org/10.3390/antibiotics10101196

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Abstract

This study aims to explore the co-occurrence of chromosomal and plasmid blaOXA-23 in carbapenem-resistant A. baumannii (CRAB) and its influence on phenotypes. A total of 11 CRAB isolates containing copies of blaOXA-23 on the chromosome and plasmid (CO), as well as 18 closely related isolates with blaOXA-23, located on either the chromosome or plasmid (SI), were selected for the determination of antibiotic susceptibility, virulence phenotype, and characteristic genomic differences. The co-occurrence of blaOXA-23 on the CRAB chromosome and plasmids did not enhance carbapenem resistance, but trimethoprim/sulfamethoxazole exhibited significantly reduced minimum inhibitory concentrations in CO. CO demonstrated a higher degree of fitness compared to SI. An increased biofilm formation ability and serum tolerance were also identified in CO, which may be associated with virulence genes, which include csuD, entE, pgaA, and plc. blaOXA-23-carrying transposons were found at different insertion sites on the chromosome. The most common site was AbaR-type genomic islands (50%). Two types of plasmids were found in CO. The co-occurrence of blaOXA-23 on the chromosome and a plasmid in CRAB had little effect on carbapenem susceptibility but was accompanied by increased fitness and virulence. Different origins and independent insertions of blaOXA-23-carrying transposons were identified in both the chromosomal and plasmid sequences.

Highlights

Acinetobacter baumannii is a Gram-negative, opportunistic, and nosocomial pathogen that causes hospital- and community-acquired infections
The analysis indicated that isolates were roughly grouped into three distinct clades, with little evidence showing that chromosome and plasmid (CO) evolved from current SI isolates, implying that co-occurrence of blaOXA-23 on chromosomes and plasmids occurred previously
Our results suggest that this may be correlated with fitness enhancement. blaOXA-23 co-occurrence on chromosomes and plasmids altered bacterial phenotypes that are important for bacterial fitness

Summary

Introduction

Acinetobacter baumannii is a Gram-negative, opportunistic, and nosocomial pathogen that causes hospital- and community-acquired infections. This pathogen is considered a global threat to public health because of the speed at which it develops resistance to antibiotics and because residual options for treating its infections are limited. A recent review reported a carbapenem-resistant Acinetobacter baumannii (CRAB) prevalence of about 80% in China [1]. Poor clinical outcomes have been reported with CRAB infections [2]. They are members of the β-lactam family that are active against most β-lactamase-producing organisms. The increasing trend in the occurrence of CRAB indicates that last-resort treatments are increasingly ineffective. Carbapenem resistance may be attributed to modified porins, penicillin-binding proteins, and the resistance-nodulationdivision (RND) family efflux system [3]

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