A method for screening tigecycline-resistant gene tet(X) from human gut

Area of Science:

• Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• The tet(X) gene confers resistance to tetracycline-class antibiotics.
• Emergence of antibiotic resistance, particularly to last-resort drugs like tigecycline, is a significant global health threat.
• Understanding the mechanisms of resistance, such as those mediated by tet(X) variants, is crucial for effective treatment strategies.

Purpose of the Study:

• To develop and validate an efficient enrichment and detection method for the tet(X) gene.
• To investigate the prevalence of tet(X) variants, specifically tet(X4), in bacterial isolates.
• To determine the association between tet(X) carriage and tigecycline resistance in *Escherichia coli*.

Main Methods:

• Polymerase chain reaction (PCR) and Sanger sequencing were employed for tet(X) gene detection and confirmation.
• Bacterial species identification was performed using Matrix-Assisted Laser Desorption/Ionization–Time of Flight Mass Spectrometry (MALDI-TOF MS).
• Minimum Inhibitory Concentrations (MICs) for common antibiotics were determined via broth microdilution, with results interpreted using CLSI and EUCAST guidelines.

Main Results:

• The study identified 29 isolates (2.26%) of *Escherichia coli* positive for the tet(X4) gene.
• A high proportion, 96.6% (28 isolates), of these tet(X4)-positive *E. coli* exhibited resistance to tigecycline.
• This indicates a strong correlation between the presence of tet(X4) and tigecycline resistance in the studied isolates.

Conclusions:

• The developed screening strategy is effective for detecting functional tet(X) genes.
• This method facilitates the identification of bacteria mediating tigecycline resistance.
• The findings contribute to a better understanding of tet(X) gene dissemination and its role in tigecycline resistance.