This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility:



Targeting resistance to a crucial reserve antibiotic

Targeting resistance to a crucial reserve antibiotic
Specific cleavage of MCR-1 by DegP. (A) Immunoblot of MCR-1 in periplasmic fractions of clinical E. coli isolates V163, NRZ14408, E. coli 023, E. coli 053, and E. coli 032 carrying the mcr-1 gene. Full-length (55 kDa) and cleaved (38 kDa) forms of the protein were detected in all isolates regardless of MICs of colistin. (B) Purification of MCR-1 and detection of a cleaved 38 kDa derivative as observed by Coomassie blue staining following SDS-PAGE. Edman sequencing identified the 38 kDa polypeptide as a fragment of MCR-1 following its cleavage at aa 198. Lane 1, His-tagged purified MCR-1; lanes 2 and 3, MCR-1; lanes 4 and 5, MCR-1199–541 following size exclusion chromatography. The full-length protein obtained from this experiment was used for the cleavage studies whose results are presented in panel D and Fig. 2F. (C) Location of the DegP cleavage site within the PBD connecting the N- and C-terminal domains of MCR-1. The crystal structure of MCR-1 was modeled using RoseTTAFold. The different regions of the proteins are labeled and depicted in different colors. (D) Coomassie-stained SDS-PAGE following incubation of purified MCR-1 with DegP. Lane 1, MW ladder; lane 2, MCR-1; lane 3, DegP; lane 4, DegP and MCR-1 coincubated. DegP* is a self-cleavage product of DegP. (E) Amino acid sequence of the PBD (aa 181 to 237) with the DegP cleavage site at aa 198 (in pink). (F) Comparison of the PBD of phylogenomically distant alleles of MCR-1 (see also Fig. S6). Credit: Microbiology Spectrum (2023). DOI: 10.1128/spectrum.03592-22

Colistin is a cationic cyclic peptide that disrupts bacterial cell membranes of Gram-negative bacteria. It is one of the few remaining antibiotics of last resort for use against infections with multidrug-resistant bacteria. Hence, the recent global detection of transferable mobile colistin resistance gene families in a wide range of multi-resistant Gram-negative bacteria isolated from all kinds of environments—clinical, veterinary, food-products and aquaculture—has sounded alarm bells.

Nevertheless, the success of mcr-1 as a transferable resistance factor remained puzzling, as its expression imposes a selective disadvantage on the growth properties of bacteria while imparting only moderate levels of resistance towards colistin.

Now, an international team led by scientists of the German Center for Infection Research (DZIF) uncovered why mcr-1—despite its drawbacks—is beneficial to bacteria. Their study suggests that acquiring mcr-1 induces a specific physiological state in bacteria that promotes resistance towards commonly encountered environmental stress conditions such as changes in acidity and antimicrobial peptides.

"We discovered that bacteria harboring mcr-1 trigger regulatory components of the bacterial envelope stress response, a system that senses fluctuations in nutrient availability and environmental changes. This in turn greatly increases MCR-1 production and promotes bacterial survival in low pH environments," says the paper's first author Dr. Renate Frantz from the Department of Medical Microbiology at Justus-Liebig University in Giessen, Germany.

The results suggest that integration of MCR-1-dependent resistance activity into the envelope stress response would support resistance of strains in environments that are stressful to , such as during passage through the or when exposed to .

"Our analyses further showed, that production of the protein MCR-1 in bacteria grown under moderately acidic conditions leads to increased modification of lipid A, the anchor structure of lipopolysaccharides—a crucial component of the bacterial membrane required for colistin resistance," says Dr. Nicolas Gisch, joint first author from the Research Center Borstel, Leibniz Lung Center.

Based on the finding, that MCR-1 enzyme activity is greatly increased under , the research team developed a simple and easily reproducible assay to reliably determine MCR-1-dependent colistin resistance in bacterial isolates.

Production of the MCR-1 protein also induces expression of DegP, a protease in the bacteria's periplasm (the space between the inner and the in Gram-negative bacteria), which cleaves MCR-1 at a specific site within a highly conserved region of the protein. "Modification of the cleavage site of MCR-1 has profound effects on both resistance activity and the triggering of the envelope stress response," adds co-lead author Dr. Konrad Gwozdzinski, former DZIF researcher and now a Senior Scientist at Mondelēz International.

These insights into the biomolecular basis of MCR-1-dependent resistance allowed the team to develop a general strategy that employs targeted activation of a protease to eliminate mcr-1-bearing plasmids from their bacterial hosts.

"Development of a simple diagnostic assay has important implications for ensuring the future use of the last-resort antibiotic colistin in ," comments Prof. Trinad Chakraborty, former Director of the Institute of Medical Microbiology at Justus Liebig University, who led the study. "Our data also allowed us to devise a novel approach to eliminate transferable colistin in Gram-negative bacteria to counter its dissemination and spread in the environment."

The research is published in the journal Microbiology Spectrum.

More information: Renate Frantz et al, A Single Residue within the MCR-1 Protein Confers Anticipatory Resilience, Microbiology Spectrum (2023). DOI: 10.1128/spectrum.03592-22

Provided by Deutsches Zentrum für Infektionsforschung

Citation: Targeting resistance to a crucial reserve antibiotic (2023, May 10) retrieved 7 December 2023 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Explore further

Researchers develop targeted test for antibiotic resistance in clinical Enterobacter species


Feedback to editors