Microevolution in the major outer membrane protein OmpA ofAcinetobacter baumannii

Abstract

Acinetobacter baumannii is nowadays a relevant nosocomial pathogen characterized by multidrug resistance (MDR) and concomitant difficulties to treat infections. OmpA is the most abundant A. baumannii outer membrane (OM) protein, and is involved in virulence, host cell recognition, biofilm formation, regulation of OM stability, permeability, and antibiotic resistance. OmpA members are two-domain proteins with an N-terminal eight-stranded β-barrel domain with four external loops (ELs) interacting with the environment, and a C-terminal periplasmic domain binding non-covalently to the peptidoglycan. Here, we combined data from genome sequencing, phylogenetic, and multilocus sequence analyses from 242 strains of the Acinetobacter calcoaceticus/Acinetobacter baumannii complex (ACB), 222 from A. baumannii, to explore ompA microevolutionary divergence. Five major ompA variant groups were identified (V1 to V5) comprising 50 different alleles coding for 29 different proteins. Polymorphisms were concentrated in 5 regions corresponding to the four ELs and the C-terminal end, and provided evidence for different intra-genic recombination events. ompA variants were not randomly distributed across the A. baumannii phylogeny, with the most frequent V1a1 allele almost exclusive to clonal complex 1 (CC1) strains and the second most frequent V2a1 allele found in the majority of CC2 strains. Evidence was found for assortative exchanges of ompA alleles not only between different A. baumannii clonal lineages, but also different ACB species. Within A. baumannii ompA non-synonymous substitutions were concentrated in the ELs regions, but were more abundant in the transmembrane regions between different Acinetobacter species. The overall results have implications for A. baumannii evolution, epidemiology, virulence, and vaccine design.ImportanceAcinetobacter baumannii is an increasing MDR threat in nosocomial settings associated with prolonged hospitalization and concomitantly increased healthcare costs. The main A. baumannii OM protein, OmpA, is a multifaceted two-domain protein implicated in host cell recognition and adhesion, cytotoxicity, biofilm formation, and as a slow porin for antibiotics and small hydrophilic nutrients. A. baumannii OmpA has been proposed as a potential target for anti-virulence drugs and as a vaccine candidate. Given the many interactions of this protein with environmental factors including host defenses, it is certainly subjected to many selective pressures. Here, we analyzed the microevolution of this OM protein in the A. baumannii population to obtain clues on the extent to which selection in the clinical setting has shaped this protein. The results provide relevant information on the main causes driving evolution of this protein, with potential implications in A. baumannii epidemiology, virulence, and vaccine design.

Virulence role of the outer membrane protein CarO in carbapenem-resistant Acinetobacter baumannii

“…Structural differences at the EL loops are most likely responsible for the differential permeation efficiencies between CarO variants toward the basic amino acid ornithine, with variant I (found in A. baumannii ATCC 19606) showing higher ornithine permeability as compared to variant IV (present in A. baumannii ATCC 17978) [21]. Thus, and similarly to A. baumannii OmpA also exhibiting sequence polymorphisms [44], there are grounds to support the notion that general CarO inhibitors could be also developed against this nosocomial pathogen. As we show in this work different CarO variants, irrespective of their differences at the EL regions [21], participate in the adherence and invasion of human lung epithelial cells (Figure 4).…”

Diversity of carbapenem-resistantAcinetobacter baumanniiand bacteriophage-mediated spread of the Oxa23 carbapenemase

“…The Sequence Read Archive was searched using keywords of Middle Eastern countries, and the genomes of an additional 36 strains were downloaded and included in subsequent analyses. The genomes of a further 17 geographically and genomically diverse strains (35) were also downloaded and included in subsequent analyses. The core genome content of the strain collection was determined using Roary v3.12.0 (36), and the core gene phylogeny estimated using FastTree v2.1.10 (37).…”

The Outer Membrane Proteins OmpA, CarO, and OprD of Acinetobacter baumannii Confer a Two-Pronged Defense in Facilitating Its Success as a Potent Human Pathogen

“…All these observations in the host indicate that OmpA might be toxic in nature, unlike other outer membrane proteins. The toxicity of A. baumannii OmpA can be attributed to its unique structural features and vast diversity of alleles ( Viale and Evans, 2020 ) with conserved domains. OmpA protein is comprised of two domains; an N-terminal 8-stranded β-barrel domain and a C-terminal periplasmic peptidoglycan binding domain.…”