Research Article

Molecular and Functional Characterization of CTX-M-15 Associated Outer Membrane Vesicles, Complement Resistance, and Macrophage Responses in Extraintestinal Pathogenic Escherichia coli Isolates from Najaf

Abstract

Background: Extraintestinal pathogenic Escherichia coli (ExPEC) commonly causes urinary tract and bloodstream infections. The worldwide spread of extended-spectrum β-lactamase (ESBL)-producing E. coli especially strains that carry blaCTX-M-15 has made treatment more difficult. Methods: Thirty clinical ExPEC isolates collected in Najaf government (Iraq) were divided into a β-lactam susceptible, ESBL-negative group (GI, n=15) and a CTX-M-15-producing group (GII, n=15). β-Lactamase activity was determined in whole-cell lysates, extracellular fractions, and purified OMVs. OMV production and protein content were characterized by nanoparticle analysis and protein quantification. Complement susceptibility was evaluated using fresh and heat-inactivated serum, together with flowcytometric assessment of C3b and C5b-9 deposition. Results: GII isolates demonstrated substantially higher β-lactamase activity than GI isolates in whole-cell lysates, extracellular fractions, and purified OMVs (all P<0.001). OMV production was approximately 2.8 fold higher in GII than in GI, while β-lactamase activity normalized to OMV particle number was approximately 8.1-fold higher (P<0.001). GII isolates exhibited greater survival in fresh serum (28.7 ± 5.3% versus 4.2 ± 1.1%, P<0.001) and reduced deposition of C3b and C5b-9. Macrophage phagocytosis was lower for GII isolates, whereas intracellular survival was significantly increased at 6 and 24 h. GII infection was associated with reduced ROS production and a cytokine profile characterized by lower TNF-α, IL-6, and IL-1β and higher IL-10 concentrations. Deletion of blaCTX-M-15 markedly reduced β-lactamase activity, OMV production, intracellular survival, and complement resistance, whereas complementation restored the phenotype. Conclusion: CTX-M-15-producing ExPEC isolates display coordinated changes in OMV-associated β-lactamase activity, complement susceptibility, and macrophage antibacterial responses. The persistence of these differences in antibiotic-free conditions and their attenuation following blaCTX-M-15 deletion support an association between the CTX-M-15 determinant and altered host–pathogen interactions. 

Authors affiliation:

Ameer Hayder Razzaq Kaiwan (ORCID): College of Health and Medical Techniques, University of Alkafeel, Najaf, Iraq.

How To Cite: A.H.R. Kaiwan. Molecular and Functional Characterization of CTX-M-15 Associated Outer Membrane Vesicles, Complement Resistance, and Macrophage Responses in Extraintestinal Pathogenic Escherichia coli Isolates from Najaf. Interdisciplinary Studies on Applied Science, 3(2):48–54, 2026. https://doi.org/10.58613/isas326