Molecular characterization and transmission pattern of tetracycline resistance determinants in tigecycline and carbapenem resistant Klebsiella pneumoniae isolates at a tertiary care hospital in India

Abstract Background. The increasing prevalence of tigecycline and carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a serious challenge, especially in resource-limited settings. Its ability to exchange resistance genes with other bacteria accelerates the spread of multidrug resistance. While carbapenems and tetracyclines have been used effectively against K. pneumoniae, resistance to these agents is now rising globally, narrowing available treatment options. Objective. The study aimed to determine the phenotypic and genotypic prevalence of carbapenem and tetracycline resistance in K. pneumoniae isolates along with the transferability pattern of carbapenem and tetracycline resistance genes in these isolates. Methodology. Clinical isolates from pus and respiratory samples were identified using biochemical tests and MALDI-TOF MS. Antimicrobial susceptibility test was performed by the Kirby–Bauer disc diffusion method, and MICs were determined by the broth microdilution test method. PCR was performed to detect carbapenemase (blaNDM, blaOXA-48 and blaKPC) and tetracycline resistance genes [tet(A), tet(B), tet(K), tet(M) and tet(S)], followed by Sanger sequencing for validation. Conjugation assays assessed gene transferability. Results. Out of 152 CRKP isolates, 20.4% (31 out of 152) were found to be resistant to tigecycline. All tigecycline-resistant isolates exhibited complete resistance (31 out of 31; 100%) to ceftazidime, ciprofloxacin and omadacycline. Additionally, resistance to amikacin and cefoperazone-sulbactam was observed in 87.1% (27 out of 31) and 77.4% (24 out of 31) of the isolates. Resistance to minocycline and colistin was detected in 51.6% (16 out of 31) and 29.0% (9 out of 31) of the isolates, respectively. PCR analysis revealed that 51.6% (16 out of 31) of the isolates carried the blaOXA-48 gene, and 29.0% (9 out of 31) carried the blaNDM gene. None of the isolates harboured the blaKPC gene. With respect to tetracycline resistance determinants, the tet(A) gene was detected in 12.9% (4 out of 31) of the isolates, and the tet(B) gene in 3.2% (1 out of 31), while tet(K), tet(M), tet(S) and blaKPC were not detected in any isolate. Conjugation assays demonstrated that plasmids carrying blaNDM and blaOXA-48 were transferable to a recipient strain, indicating their potential for horizontal gene transfer. In contrast, plasmids harbouring tet(A) and tet(B) genes were not transferable under the experimental conditions. Conclusion. Tigecycline-resistant K. pneumoniae isolates showed high multidrug resistance, with transferable blaNDM and blaOXA-48 genes. In contrast, chromosome and plasmid-borne tetracycline resistance genes tet(A) and tet(B) were non-transferable, indicating limited horizontal spread.