Fundamental changes in the antimicrobial resistance profile of Klebsiella quasipneumoniae ATCC 700603 in response to meropenem stress

TL;DR

This study shows how Klebsiella quasipneumoniae develops resistance to meropenem through carbapenemase production after prolonged exposure.

Contribution

Demonstrates meropenem resistance in K. quasipneumoniae via carbapenemase overexpression, not horizontal gene transfer.

Findings

Fully adapted cells showed 256-fold higher meropenem resistance than parent cells.

Carbapenemases degraded 65.93% of meropenem in resistant cells.

The blaOXA-2 gene was overexpressed 3.12-fold in resistant cells.

Abstract

Klebsiella is one of the most challenging superbugs having a high tendency to acquire rapid resistance to many antibiotics, even the ones recognized as the last resort. In several hospitals and environmental niches, Klebsiella is continuously exposed to residual amounts of antibiotics at sub-inhibitory concentrations forming an environmental stress motivating them to adapt and evolve antimicrobial resistance. In the present study, meropenem (MEM) resistance was induced experimentally in a MEM-sensitive strain of K. quasipneumoniae ATCC 700603 through sequential sub-culturing in presence of sub-inhibitory concentrations of MEM over a period of 20 days. To uncover the possible mechanisms standing behind the evolution of antimicrobial resistance upon successive exposure to stress of MEM rather than horizontal gene transfer (HGT) of antibiotic resistance genes.

Fully adapted cells of the 20th generation (G20) showed MEM-resistance with elevated minimum inhibitory concentration (MIC) by 256-fold compared to the parent cells (G0). The main mechanism of resistance was the production of carbapenemases, which was assured by different tests including nitrocefin, modified-Hodge test (MHT), and modified carbapenem inactivation method (mCIM). The degradation of MEM reached 65.93% by the produced carbapenemases of G20 as determined by the HPLC analysis. Transcriptomics analysis of the class D carbapenemase encoding gene, blaOXA-2, revealed that it was significantly over-expressed by a 3.12-fold (p < 0.05) in G20 compared to G0.

The evolved MEM resistance aroused mainly from MEM degradation by carbapenemases, neither increased efflux nor decreased influx of MEM. The rational use of antibiotics is essential to reduce bacterial exposure to the environmental basal levels of antibiotics and decreasing the evolution of antimicrobial resistance.

The online version contains supplementary material available at 10.1186/s12866-025-04100-6.

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