Subtle Difference Generates Big Dissimilarity: Comparison of Enzymatic Activity in KL1 and KL2 Domains of Lancelet Klotho

Combining with matrine restores ciprofloxacin efficacy against qnrS producing E. coli in vitro and in vivo

The exposure risk of plasmid-mediated quinolone resistance (PMQR) genes increases the incidence of resistant bacterial infections, has resulted in clinical treatment failures with ciprofloxacin, necessitating urgent implementation of novel strategies for controlling this situation. Matrine serves as the principal constituent of the traditional Chinese herb Sophora flavescens Ait. and exhibits pharmacological activities including anti-inflammatory, antibacterial, anti-tumor, and hepatoprotective effects. However, the precise mechanism by which matrine exhibits antibacterial activity remains incompletely elucidated. This study investigated the antibacterial potential and synergistic mechanism of matrine in combination with ciprofloxacin against qnrS-carrying E. coli. The clinical ciprofloxacin-resistant E. coli carrying the qnrS and the recombinant E. coli DE3 (pET28a-qnrS) were evaluated for their antibacterial activity in vitro, it was found that the combination of matrine/ciprofloxacin exhibited a significant synergistic, reducing the MIC value of ciprofloxacin against qnrS-positive E. coli by 4-fold, and it effectively reduced the bacterial load to undetectable levels within 10 h without obvious cytotoxicity. Moreover, consistent findings were observed in significantly reducing bacterial load within the mouse infection model. Molecular docking revealed that matrine was localized in the large loop B of the qnrS crystal structure, establishing hydrogen bonds with Thr-102 and Arg-101, thereby disrupting the activity of qnrS. Interaction analysis further confirmed that matrine could significantly inhibit the protective effect of qnrS on gyrase and restore the activity of ciprofloxacin against qnrS-positive E. coli. Matrine may serve as a qnrS inhibitor to restore the efficacy of ciprofloxacin, suggesting its potential as a novel antibiotic adjuvant for controlling bacterial infections.

Palmatine Is a Plasmid-Mediated Quinolone Resistance (PMQR) Inhibitor That Restores the Activity of Ciprofloxacin Against QnrS and AAC(6')-Ib-cr-Producing Escherichia coli

Purpose

The emergence of plasmid-mediated quinolone resistance (PMQR) is a global challenge in the treatment of clinical disease in both humans and animals and is exacerbated by the presence of different PMQR genes existing in the same bacterial strain. Here, we discovered that a natural isoquinoline alkaloid palmatine extracted from traditional Chinese medicinal plants effectively inhibited the activity of PMQR proteins QnrS and AAC(6′)-Ib-cr.

Methods

In total 120 clinical ciprofloxacin-resistant Escherichia coli (E. coli) were screened for the presence of qnrS and aac(6ʹ)-Ib-cr by PCR. Recombinant E. coli that produced QnrS or AAC(6ʹ)-Ib-cr proteins were constructed and the correct expression was confirmed by MALDI/TOF MS analysis and SDS-PAGE. A minimal inhibitory concentration (MICs) assay, growth curve assay and time-kill assay were conducted to evaluate the in vitro antibacterial activity of palmatine and the combination of palmatine and ciprofloxacin. Cytotoxicity assays and mouse thigh infection model were used to evaluate the in vivo synergies. Molecular docking, gyrase supercoiling assay and acetylation assay were used to clarify the mechanism of action.

Results

Palmatine effectively restored the activity of ciprofloxacin against qnrS and aac(6ʹ)-Ib-cr-positive E. coli strains in a synergistic manner in vitro. In addition, the combined therapy significantly reduced the bacterial burden in a mouse thigh infection model. Molecular docking revealed that palmatine bound at the functional large loop B of QnrS and Trp102Arg and Asp179Tyr in the binding pocket of AAC(6′)-Ib-cr. Furthermore, interaction analysis confirmed that palmatine reduced the gyrase protective effect of QnrS and the acetylation effect of AAC(6′)-Ib-cr.

Conclusion

Our findings suggest that palmatine is a potential efficacious compound to restore PMQR-mediated ciprofloxacin resistance and warrants further preclinical evaluations.