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Outer membrane vesicles of carbapenem-resistant Acinetobacter baumannii derive enhanced inflammatory response

ABSTRACT: Carbapenem-resistant Acinetobacter baumannii (CRAB) is a critical nosocomial pathogen with limited treatment options. Although antibiotic resistance in CRAB is well-characterized, its interactions with host immunity and the contribution of outer membrane vesicles (OMVs) to pathogenesis remain poorly understood. We examined a clinical CRAB isolate and compared it with the reference strain A19606. Antimicrobial susceptibility testing revealed complete resistance of CRAB to commonly used antibiotics in clinical practice, while A19606 remained susceptible to most agents. In murine intranasal infection models and bone marrow-derived macrophages, CRAB induced significantly stronger activation of inflammatory signaling pathways and elevated levels of pro-inflammatory cytokines relative to A19606. Transcriptomic analysis of infected lung tissue identified differentially expressed genes, enriched for inflammatory response pathways. proteomics showed upregulated proteins in CRAB related to secretion systems. OMVs characterization revealed that CRAB-derived OMVs highly enriched in proteins associated with periplasmic and outer membrane spaces, and more potent in triggering macrophage inflammatory signaling. CRAB displays expansive antibiotic resistance and enhanced pro-inflammatory potential mediated in part by unique OMVs properties. Targeting OMVs formation or host immune modulation may represent effective strategies for combating CRAB infections.

ORGANISM(S): Mus musculus

PROVIDER: GSE313682 | GEO | 2026/01/19

REPOSITORIES: GEO

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Project description:Objectives: Carbapenem-resistant Acinetobacter baumannii (CRAB) are one of the most difficult pathogen to treat. The only drug recently approved by the FDA that is active against CRAB is cefiderocol. However, recent studies have shown higher all-cause mortality rate in the group of patients treated with cefiderocol, that may be due to heteroresistance, a phenotype characterized by the survival of a small proportion of cells in a population seemingly isogenic. Previous studies showed that adding human fluids to CRAB cultures can lead to CFDC heteroresistance. To better understand the nature of this phenomenon, we carried out molecular and phenotypic analyses of CRAB heteroresistant bacterial subpopulations. Methods: The CRAB strain AMA40 was cultured in the presence of cefiderocol and human pleural fluid (HPF) to isolate heteroresistant variants. Two of them, AMA40 IHC_1 and IHC_2, were subjected to whole genome sequencing and transcriptomic analysis to identify the mutations and transcriptomic changes responsible for the development of cefiderocol resistance. The impact of mutations on the pharmacodynamic activity of cefiderocol was assessed by susceptibility testing, EDTA and Boronic acid inhibition analysis, biofilm formation, and static time-kill assays. Results: Variants AMA40 IHC_1 and IHC_2 had 53 mutations, forty of which were common to both heteroresistant strains. None of the mutations are located inside genes associated with iron-uptake systems or β-lactam resistance. However, pipA, a gene associated with iron homeostasis in other species, was mutated in heteroresistant strains. Transcriptomic analyses revealed modifications in levels of expression of genes associated with antibiotic resistance. The blaNDM-1, blaADC-2, pbp3, and pbp1 were expressed at higher levels. At the same time, the carO and ompA genes’ expression was reduced. Collateral resistance to amikacin was observed in the heteroresistant variants. Static time-kill assays showed that when CA-MHB was supplemented with human serum albumin, the main protein component of HPF, cefiderocol killing activity was considerably reduced in all three strains. Conclusions: We conclude that heteroresistance to cefiderocol in CRAB, when exposed to fluids containing high HSA, is caused by mutations and modifications in the expression of genes associated with resistance to β-lactams.

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Outer membrane vesicles of carbapenem-resistant Acinetobacter baumannii derive enhanced inflammatory response

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