Transcriptomic correlates of ceftazidime-avibactam collateral sensitivity in tigecycline-resistant NDM-producing enterobacter cloacae complex.

PURPOSE: Carbapenem-resistant Enterobacter cloacae complex (CRECC) has become an increasingly important pathogen in healthcare-associated infections, with limited treatment options and a high mortality rate. As reports of antimicrobial resistance continue to rise, tigecycline (TGC) and ceftazidime-avibactam (CZA) have emerged as the last-line therapies for CRECC infections. The aim of this study was to investigate collateral sensitivity to ceftazidime-avibactam following the acquisition of tigecycline resistance in NDM-producing CRECC, and to explore the transcriptional changes associated with this phenomenon and propose potential mechanistic hypotheses.

METHODS

Antimicrobial susceptibility profiles were determined using the broth microdilution method, and changes in colony morphology were analyzed. Transcriptomic sequencing was performed to characterize global gene expression alterations associated with antimicrobial resistance, and an in vivo Galleria mellonella infection model was used to assess the virulence of the mutant strains.

RESULTS

Both drug-resistant mutants displayed a stable mucoid phenotype with marked collateral susceptibility to CZA, with minimum inhibitory concentrations decreasing from greater than 128 mg/L to 0.5-1 mg/L. Compared with the parental strains, these mutants showed thickened cell surface structures, impaired growth, reduced serum tolerance, and significantly attenuated virulence in the Galleria mellonella infection model. Transcriptomic analysis revealed marked downregulation of metallo-β-lactamase-related genes at the transcriptional level.

CONCLUSION

In this study of two clinical isolates, collateral sensitivity to CZA was associated with transcriptional downregulation of blaNDM and altered bacterial metabolism. These findings suggest a potential trade-off between tigecycline resistance and CZA susceptibility that warrants further functional validation.