AUTHOR=Bharathi Srinivasan Vijaya , Venkataramaiah Manjunath , Rajamohan Govindan 

TITLE=Genotypic and Phenotypic Characterization of Novel Sequence Types of Carbapenem-Resistant Acinetobacter baumannii, With Heterogeneous Resistance Determinants and Targeted Variations in Efflux Operons

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.738371

DOI=10.3389/fmicb.2021.738371

ISSN=1664-302X

ABSTRACT=<p><italic>Acinetobacter baumannii</italic> has emerged as one of the dominant nosocomial human pathogens associated with high morbidity and mortality globally. Increased incidences of carbapenem-resistant <italic>A. baumannii</italic> (CRAB) have resulted in an enormous socioeconomic burden on health-care systems. Here, we report the genotypic and phenotypic characterization of novel ST1816 and ST128 variants in <italic>A. baumannii</italic> strains belonging to International clone II (GC2) with capsule types KL1:OCL8 and KL3:OCL1d from India. Sequence analysis revealed the presence of diverse virulome and resistome in these clinical strains, in addition to islands, prophages, and resistance genes. The oxacillinase <italic>bla</italic><sub><italic>OXA–23</italic></sub>detected in the genomic island also highlighted the coexistence of <italic>bla</italic><sub><italic>OXA–66</italic></sub>/<italic>bla</italic><sub><italic>OXA–98</italic></sub>, <italic>bla</italic><sub><italic>ADC73</italic></sub>/<italic>bla</italic><sub><italic>ADC–3</italic></sub>, and <italic>bla</italic><sub><italic>TEM–1D</italic></sub> in their mobile scaffolds, which is alarming. Together with these resistance-determining enzymes, multidrug efflux transporters also harbored substitutions, with increased expression in CRAB strains. The hotspot mutations in colistin resistance-conferring operons, PmrAB, LpxACD, and AdeRS, were additionally confirmed. Phenotype microarray analysis indicated that multidrug-resistant strains <italic>A. baumannii</italic> DR2 and <italic>A. baumannii</italic> AB067 preferred a range of antimicrobial compounds as their substrates relative to the other. To our knowledge, this is the first comprehensive report on the characterization of <italic>A. baumannii</italic> variants ST1816 and ST128, with different genetic makeup and genome organization. The occurrence of CRAB infections worldwide is a severe threat to available limited therapeutic options; hence, continued surveillance to monitor the emergence and dissemination of such novel ST variants in <italic>A. baumannii</italic> is imperative.</p>