Whole-genome Study of Carbapenem-resistant Acinetobacter baumannii Virulence and Resistance

Background and Aim: Carbapenem-resistant Acinetobacter baumannii (CRAb) has ability to develop and acquire resistance makes it one of the most critical nosocomial pathogens globally. Whole genome sequemcing (WGS) technology was employed to map genes associated with antimicrobial resistance (AMR),virulene factors and to identify multilocus sequence types (MLST). In order to understand the resistance mechanism for A. baumannii species, this study set out to establish the genetic makeup of the species. Materials and Methods: Whole-genome sequencing (WGS) of A.b4, A.b49 and A.b75 was performed using Illumina MiSeq and the genomes were assembled with SPAdes. ARG-ANNOT, CARD-RGI, VFDB, PHAST, PlasmidFinder were used to analyse all genomes. Results: Genome analysis revealed that Ab4 belongs to ST944, represented singletons that could not be attributed to any, A.b49 belongs to ST1104, represented unique ST.While A.b75 belongs to ST195 which represented known international clones of high risk .Molecular characterisation showed the presence 23 antibiotic resistance genes in all straines of A. baumannii. 12 of them are shared by all 3 strains and 11 are common between A. baumannii 4(ST/944), 49 (ST/1104) and 75(ST/195). The common drug-resistance genes shared by all 3 strains include bla OXA-72 (resistance to carbapenems), ade genes, RND (adeFJK, adeLN  adeR), and SMR   (abeS) encoding for efflux pumps. Conclusion: We present WGS analysis of three A. baumannii strains belonging to three different STs. The presence of strains harboring acquired AMR genes makes them more dangerous. Acquired resistance genes and chromosomal gene mutation are successful routes for disseminating AMR determinants among A. baumannii. Identification of chromosomal and plasmid-encoded AMR in the genome of A. baumannii may help understand the mechanism behind the genetic mobilization and spread of AMR genes.