Differential Expression of blaCTX‑M‑33 with Vancomycin/ Trimethoprim Combination in Escherichia coli‑Producing Extended‑Spectrum β‑Lactamase Isolated from Intensive Care Unit‑Acquired Urinary Tract Infection

Document Type : Original Article


1 Department of Biology, Gachsaran Branch, Islamic Azad University, Gachsaran,

2 Department of Microbiology, Yasooj Branch, Islamic Azad University, Yasooj, Iran



Aim: The aim of this study was to develop combination approach for the treatment of Escherichia coli‑producing extended‑spectrum
β‑lactamases (ESBLs) isolated from intensive care unit (ICU)‑acquired urinary tract infections (UTIs). Materials and Methods: The
observational study was conducted between January 5, 2018- June 5, 2019 to isolate and detect E. coli from UTI patients admitted to ICUs
in Shahid Rajaee hospital, Gachsaran, Iran. Morphological, biochemical and molecular methods were conducted to identify E. coli isolates.
Phenotypic confirmation of E. coli producing ESBL was performed using ESBL disc diffusion test according to the Clinical and Laboratory
Standards Institute (CLSI) guidelines. The combination index assay set‑up was based on CLSI guidelines to investigate antibacterial
susceptibilities to vancomycin alone and in combination with trimethoprim and interpreted with the fractional inhibitory concentration (FIC)
index. Eventually, the expression levels of blaCTX‑M‑33 gene were determined by real‑time quantitative reverse transcription–polymerase chain
reaction. Results: A total of 90 ICU‑acquired UTIs occurred among 255 patients. The combination index assay results showed that vancomycin/
trimethoprim combination would be reduced its minimal inhibitory concentration90 value. The vancomycin/trimethoprim combination revealed
partial synergistic and indifferent effects (FIC = 0.52–1.50) in the isolates of E. coli‑producing ESBL. The results of gene expression analysis
indicated that vancomycin/trimethoprim combination caused downregulation of blaCTX‑M‑33 gene at negligible levels by 55.56–58.82‑fold and
stopped drug resistant. Conclusion: Vancomycin/trimethoprim combination may diminish resistance in the E. coli‑producing ESBL isolated
from ICU‑acquired UTI patients.