AUTHOR=Roy Subhasree , Chatterjee Somdatta , Bhattacharjee Amrita , Chattopadhyay Pinaki , Saha Bijan , Dutta Shanta , Basu Sulagna 

TITLE=Overexpression of Efflux Pumps, Mutations in the Pumps’ Regulators, Chromosomal Mutations, and AAC(6′)-Ib-cr Are Associated With Fluoroquinolone Resistance in Diverse Sequence Types of Neonatal Septicaemic Acinetobacter baumannii: A 7-Year Single Center Study

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.602724

DOI=10.3389/fmicb.2021.602724

ISSN=1664-302X

ABSTRACT=<p>This study investigates susceptibility toward three fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin), multiple fluoroquinolone-resistance mechanisms, and epidemiological relationship of neonatal septicaemic <italic>Acinetobacter baumannii</italic>. Previous studies on fluoroquinolone resistance in <italic>A. baumannii</italic> focused primarily on ciprofloxacin susceptibility and assessed a particular mechanism of resistance; a more holistic approach was taken here. Epidemiological relationship was evaluated by Multi Locus Sequence Typing. Minimum Inhibitory Concentrations of fluoroquinolones was determined with and without efflux pump inhibitors. Overexpression of efflux pumps, resistance-nodulation-cell-division (RND)-type, and multidrug and toxic compound extrusion (MATE)-type efflux pumps were evaluated by reverse transcriptase-qPCR. Mutations within regulatory proteins (AdeRS, AdeN, and AdeL) of RND-pumps were examined. Chromosomal mutations, presence of <italic>qnr</italic> and <italic>aac(6</italic>′<italic>)-Ib-cr</italic> were investigated. <italic>A. baumannii</italic> were highly diverse as 24 sequence-types with seven novel STs (ST-1440/ST-1441/ST-1481/ST-1482/ST-1483/ST-1484/ST-1486) were identified among 47 <italic>A. baumannii.</italic> High resistance to ciprofloxacin (96%), levofloxacin (92%), and particularly moxifloxacin (90%) was observed, with multiple mechanisms being active. Resistance to 4<sup>th</sup> generation fluoroquinolone (moxifloxacin) in neonatal isolates is worrisome. Mutations within GyrA (S83L) and ParC (S80L) were detected in more than 90% of fluoroquinolone-resistant <italic>A. baumannii</italic> (FQRAB) spread across 10 different clonal complexes (CC1/CC2/CC10/CC25/CC32/CC126/CC149/CC216/CC218/CC513). Efflux-based FQ resistance was found in 65% of FQRAB with ≥2 different active pumps in 38% of strains. Overexpression of <italic>adeB</italic> was highest (2.2−34-folds) followed by <italic>adeJ</italic>, <italic>adeG</italic>, and <italic>abeM</italic>. Amino acid changes in the regulators (AdeRS/AdeN/AdeL) either as single or multiple substitutions substantiated the overexpression of the pumps. Diverse mutations within AdeRS were detected among different CCs whereas mutations within AdeN linked to CC10 and CC32. Chromosomal mutations and active efflux pumps were detected simultaneously among 64% of FQRAB. Presence of <italic>aac(6′)-Ib-cr</italic> was also high (74% of FQRAB) but <italic>qnrS</italic> were absent. As most FQRABs had chromosomal mutations, this was considered predominant, however, isolates where pumps were also active had higher MIC values, establishing the critical role of the efflux pumps. The high variability of FQ susceptibility among FQRAB, possessing the same set of mutations in <italic>gyrA</italic>, <italic>parC</italic>, and efflux pump regulators, was also noted. This reveals the complexity of interpreting the interplay of multiple resistance mechanisms in <italic>A. baumannii</italic>.</p>