Phenotypic Characterization and Heterogeneity among Modern Clinical Isolates of Acinetobacter baumannii

Adam Valcek, Chantal Philippe, Clémence Whiteway, Etienne Robino, Kristina Nesporova, Mona Bové, Tom Coenye, Tim De Pooter, Wouter De Coster, Mojca Strazisar, Charles Van der Henst

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Acinetobacter baumannii is an opportunistic pathogenic bacterium prioritized by WHO and CDC because of its increasing antibiotic resistance. Heterogeneity among strains represents the hallmark of A. baumannii bacteria. We wondered to what extent extensively used strains, so-called reference strains, reflect the dynamic nature and intrinsic heterogeneity of these bacteria. We analyzed multiple phenotypic traits of 43 nonredundant, modern, and multidrug-resistant, extensively drug-resistant, and pandrug-resistant clinical isolates and broadly used strains of A. baumannii. Comparison of these isolates at the genetic and phenotypic levels confirmed a high degree of heterogeneity. Importantly, we observed that a significant portion of modern clinical isolates strongly differs from several historically established strains in the light of colony morphology, cellular density, capsule production, natural transformability, and in vivo virulence. The significant differences between modern clinical isolates of A. baumannii and established strains could hamper the study of A. baumannii, especially concerning its virulence and resistance mechanisms. Hence, we propose a variable collection of modern clinical isolates that are characterized at the genetic and phenotypic levels, covering a wide range of the phenotypic spectrum, with six different macrocolony type groups, from avirulent to hypervirulent phenotypes, and with naturally noncapsulated to hypermucoid strains, with intermediate phenotypes as well. Strain-specific mechanistic observations remain interesting per se, and established "reference" strains have undoubtedly been shown to be very useful to study basic mechanisms of A. baumannii biology. However, any study based on a specific strain of A. baumannii should be compared to modern and clinically relevant isolates. IMPORTANCE Acinetobacter baumannii is a bacterium prioritized by the CDC and WHO because of its increasing antibiotic resistance, leading to treatment failures. The hallmark of this pathogen is the high heterogeneity observed among isolates, due to a very dynamic genome. In this context, we tested if a subset of broadly used isolates, considered "reference" strains, was reflecting the genetic and phenotypic diversity found among currently circulating clinical isolates. We observed that the so-called reference strains do not cover the whole diversity of the modern clinical isolates. While formerly established strains successfully generated a strong base of knowledge in the A. baumannii field and beyond, our study shows that a rational choice of strain, related to a specific biological question, should be taken into consideration. Any data obtained with historically established strains should also be compared to modern and clinically relevant isolates, especially concerning drug screening, resistance, and virulence contexts.

Original languageEnglish
Article numbere0306122
Number of pages16
JournalMicrobiology spectrum
Issue number1
Early online date8 Dec 2022
Publication statusPublished - Jan 2023

Bibliographical note

Funding Information:
This project was supported by the Flanders Institute for Biotechnology (VIB) and has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no. 748032. A.V. is a recipient of a junior postdoctoral fellowship of the Research Foundation – Flanders (FWO; file number 1287223N). K.N. was supported by the Erasmus 1 program KA131-HED.

Publisher Copyright:
© 2022 Valcek et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.

Copyright 2023 Elsevier B.V., All rights reserved.


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