Abundance of Colistin-Resistant, OXA-23- and ArmA-Producing Acinetobacter baumannii Belonging to International Clone 2 in Greece

Mattia Palmieri; Marco Maria D'Andrea; Andreu Coello Pelegrin; Nadine Perrot; Caroline Mirande; Bernadette Blanc; Nicholas Legakis; Herman Goossens; Gian Maria Rossolini; Alex van Belkum

doi:10.3389/fmicb.2020.00668

Abundance of Colistin-Resistant, OXA-23- and ArmA-Producing Acinetobacter baumannii Belonging to International Clone 2 in Greece

Front Microbiol. 2020 Apr 15:11:668. doi: 10.3389/fmicb.2020.00668. eCollection 2020.

Authors

Affiliations

¹ bioMérieux, Data Analytics Unit, La Balme-les-Grottes, France.
² Department of Medical Biotechnologies, University of Siena, Siena, Italy.
³ Department of Biology, University of Rome Tor Vergata, Rome, Italy.
⁴ bioMérieux, R&D Microbiology, La Balme-les-Grottes, France.
⁵ Central Laboratories, IASO Group Hospitals, Athens, Greece.
⁶ Laboratory of Medical Microbiology, Vaccine and Infectious Disease Institute, University of Antwerp, Antwerp, Belgium.
⁷ Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy.
⁸ Clinical Microbiology and Virology Unit, Florence Careggi University Hospital, Florence, Italy.

Abstract

Carbapenem resistant Acinetobacter baumannii (CRAB) represents one of the most challenging pathogens in clinical settings. Colistin is routinely used for treatment of infections by this pathogen, but increasing colistin resistance has been reported. We obtained 122 CRAB isolates from nine Greek hospitals between 2015 and 2017, and those colistin resistant (ColR; N = 40, 32.8%) were whole genome sequenced, also by including two colistin susceptible (ColS) isolates for comparison. All ColR isolates were characterized by a previously described mutation, PmrB^A226V, which was associated with low-level colistin resistance. Some isolates were characterized by additional mutations in PmrB (E140V or L178F) or PmrA (K172I or D10N), first described here, and higher colistin minimum inhibitory concentrations (MICs), up to 64 mg/L. Mass spectrometry analysis of lipid A showed the presence of a phosphoethanolamine (pEtN) moiety on lipid A, likely resulting from the PmrA/B-induced pmrC overexpression. Interestingly, also the two ColS isolates had the same lipid A modification, suggesting that not all lipid A modifications lead to colistin resistance or that other factors could contribute to the resistance phenotype. Most of the isolates (N = 37, 92.5%) belonged to the globally distributed international clone (IC) 2 and comprised four different sequence types (STs) as defined by using the Oxford scheme (ST 425, 208, 451, and 436). Three isolates belonged to IC1 and ST1567. All the genomes harbored an intrinsic bla _OXA-51 group carbapenemase gene, where bla _OXA-66 and bla _OXA-69 were associated with IC2 and IC1, respectively. Carbapenem resistance was due to the most commonly reported acquired carbapenemase gene bla _OXA-23, with ISAba1 located upstream of the gene and likely increasing its expression. The armA gene, associated with high-level resistance to aminoglycosides, was detected in 87.5% of isolates. Collectively, these results revealed a convergent evolution of different clonal lineages toward the same colistin resistance mechanism, thus limiting the effective therapeutic options for the treatment of CRAB infections.

Keywords: A. baumannii; Greece; colistin resistance; genomics; lipid A; pmrCAB.