Genomic relatedness and dissemination of blaNDM-5 among Acinetobacter baumannii isolated from hospital environments and clinical specimens in Thailand

Background: Acinetobacter baumannii (A. baumannii) is an important cause of nosocomial infection, especially in intensive care units (ICUs). It has the propensity to tolerate various environments and multiple classes of antibiotics. Our study aimed to characterize the comparative genomes of A. baumannii from hospital environments and clinical isolates. Methods: Clinical and environmental A. baumannii isolates were collected from a university hospital. Antibiotic susceptibility testing was performed, antibiotic resistance genes (ARGs) were characterized, and repetitive element palindromic-PCR (rep-PCR) typing was performed. Eight representative A. baumannii isolated from environmental and clinical samples from the same wards were selected for whole-genome sequencing (WGS) using the Illumina platform. Results: A total of 106 A. baumannii isolates were obtained from 312 hospital environmental samples. A high percentage of samples with A. baumannii colonization were detected from AMBU bags (77.9%), followed by bedrails (66.7%) and suction tubes (66.7%). We found that 93.4% of the environmental isolates were multidrug-resistant A. baumannii (MDRAB), and 44.7% were extremely drug-resistant A. baumannii (XDRAB). blaOXA-23 blaNDM, and blaOXA-58 were present in 80.2%, 78.3%, and 0.9% of all isolates, respectively. Sixty-one A. baumannii isolates were collected from patient specimens in the same ward. Among all A. baumannii clinical isolates, MDRAB and XDRAB accounted for 82% and 55.7%, respectively. The most dominant ARGs identified was blaOXA-23 (80.3%), followed by blaNDM (55.7%). The genetic diversity of all isolates using rep-PCR could be divided into 33 genotypes. The genome size of eight A. baumannii ranged from 3.78-4.01 Mb. We found six of eight strains to be blaNDM-5-harboring A. baumannii. Mobile genetic elements (MGEs), such as integron1 (intl1), located upstream of blaNDM-5 were observed. The phylogenomic relationship of the core and pan genomes as well as the single nucleotide polymorphism (SNP) count matrix revealed the genetic similarity of A. baumannii environmental and clinical strains obtained from the same ward. Conclusion: This study confirmed that A. baumannii colonized in hospital environments were the main reservoir of nosocomial infection and provides critical information to guide the control of A. baumannii infection.