Genomic characterization and identification of multiple drug resistance genes in clinical isolates of Acinetobacter baumannii through whole genome sequencing.

Background: Acinetobacter baumannii is a notorious nosocomial pathogen universally in healthcare settings. Its natural competent characteristics for genetic recombination are responsible for acquired antibiotic resistance and render it untreatable through commonly used antibiotics. Hence, characterizing the A. baumannii genomes for multidrug resistance carriage is of paramount importance. The study aimed to characterize the whole genome of clinical isolates of A. baumannii to identify specifically the types of antibiotic resistance genes, drug classes and mobile genetic elements. We also aimed to determine the significant multi-locus sequence tags (MLSTs). The phylogeny of the isolates was established with other clinical strains distributed globally.

Methods and results: Fifteen clinical isolates (isolated from tracheal secretion, urine and bronchoalveolar lavage) were subjected to whole genome sequencing. Raw sequences were assembled using SPAdes and species were identified using KmerFinder 3.2. The assembled genomes were annotated using the Prokka v1.14.6. Resfinder 4.6.0 was used to determine antibiotic resistance genes. The sequences were aligned against seven housekeeping genes aka sequence tags (STs) available within the MLST database (v 2.0.9). MobileGeneticElement finder (v1.0.3) were used for profiling mobile genetic elements associated with the antibiotic resistance genes. The genomes of nosocomial A. baumannii were assembled with an average N50 of 23,480 and GC content of 38%. There were approximately 3700 CDs, 53 tRNA and 3 rRNA. About 80% of the isolates were ST2 type. The genomes possessed antibiotic resistance genes (n = 24) belonging to 17 drug classes. The predicted phenotype was multidrug resistant. Among the mobile genetic elements, 12 insertion sequences and 2 composite transposons were also found. The mode of antibiotic resistance was mostly through antibiotic inactivation in all the isolates.

Conclusions: The results imply the occurrence of multidrug resistant genes in clinical isolates of A. baumannii strains in the healthcare settings of Kuwait. A more comprehensive survey should be undertaken for antimicrobial resistance monitoring on a regular basis for surveillance, contact tracing, and potential mitigation in clinical settings.