Version 1: Molecular characterization and transmission pattern of tetracycline resistance gene in tigecycline and carbapenem resistance klebsiella pneumoniae isolates at a tertiary care hospital India

Introduction 

Significant rise in resistance to tigecycline in carbapenem resistant K. pneumoniae (CRKP) is now a common concern in developing countries. Seeing these issues, we aimed to determine the genetic prevalence of tetracycline resistance gene along with transferability pattern in tigecycline resistant K. pneumoniae. 

Methodology

All K. pneumoniae isolates were isolated from pus and sputum samples and identified by MALDI-TOF MS. MIC of tigecycline resistance isolates were done by broth micro dilution method and Genetic characterization of Carbapenemases (blaNDM, blaOXA-48 and blaKPC) and tetracycline (tetA, tetB, tetK, tetM and tetS) genes were performed by PCR and Sanger sequencing, while transmission pattern was checked by conjugation assay. 

Results

Of 152 K. pneumoniae isolates, 20.4% (31/152) were resistant to tigecycline. The MIC50/MIC90 of imipenem, meropenem, tigecycline and omadacycline were 256/512 μg/ml, 128/512 μg/ml, 16/64 μg/ml and 16/128 μg/ml respectively. Furthermore, all isolates were resistant to Ceftazidime, Ceftriaxone, Aztreonam, Gentamicin, Ciprofloxacin with more than high MIC of >256μg/ml. However, only 51.6% (16/31) and 29.1% (9/31) isolates were resistant to minocycline and colistin. PCR result indicated that, 12.9% (4/31) contain tet(A) gene, 3.22% (1/31) contain tet(B) gene, 51% (16/31) isolates contain blaOXA-48 and 29% (9/31) isolate contain blaNDM gene while there are no isolates that contain tet(K), tet(M), tet(S)and blaKPC. The conjugation assay revealed that plasmid containing genes of blaNDM and blaOXA are transferable while tet(A) and tet(B) are non-transferable. 

Conclusion 

Our study revealed that Chromosome and plasmid-borne tet(A) gene increase MIC of tigecycline in carbapenem-resistant K. pneumoniae while the tet(B) gene is rare. This discovery underscores a potential threat that warrants closer attention.