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MgrB Inactivation Is Responsible for Acquired Resistance to Colistin in Enterobacter hormaechei subsp. steigerwaltii
Amel Mhaya1,2, Dominique Bégu1, Slim Tounsi2
1Laboratoire de Microbiologie Fondamentale et Pathogénicité (MFP), Université de Bordeaux, CNRS UMR-5234, Bordeaux, France.
Abstract:
Multidrug-resistant strains belonging to the Enterobacter cloacae complex (ECC) group, and especially those belonging to clusters C-III, C-IV, and C-VIII, have increasingly emerged as a leading cause of health care-associated infections, with colistin used as one of the last lines of treatment. However, colistin-resistant ECC strains have emerged. The aim of this study was to prove that MgrB, the negative regulator of the PhoP/PhoQ two-component regulatory system, is involved in colistin resistance in ECC of cluster C-VIII, formerly referred to as Enterobacter hormaechei subsp. steigerwaltii An in vitro mutant (Eh22-Mut) was selected from a clinical isolate of Eh22. The sequencing analysis of its mgrB gene showed the presence of one nucleotide deletion leading to the formation of a truncated protein of six instead of 47 amino acids. The wild-type mgrB gene from Eh22 and that of a clinical strain of Klebsiella pneumoniae used as controls were cloned, and the corresponding recombinant plasmids were used for complementation assays. The results showed a fully restored susceptibility to colistin and confirmed for the first time that mgrB gene expression plays a key role in acquired resistance to colistin in ECC strains.
Insights
The mgrB gene is crucial for colistin resistance in multidrug-resistant Enterobacter cloacae complex strains. Mutations in mgrB lead to colistin resistance, impacting treatment options for these challenging healthcare-associated infections.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- Multidrug-resistant Enterobacter cloacae complex (ECC) strains are a growing threat in healthcare settings.
- Colistin is a last-resort antibiotic, but resistance is emerging in ECC strains.
- Understanding resistance mechanisms is vital for effective treatment strategies.
Purpose of the Study:
- To investigate the role of the mgrB gene in colistin resistance within ECC cluster C-VIII (formerly Enterobacter hormaechei subsp. steigerwaltii).
- To determine if mgrB mutations contribute to acquired colistin resistance in these pathogens.
Main Methods:
- Selection of an in vitro colistin-resistant mutant (Eh22-Mut) from a clinical ECC isolate (Eh22).
- Sequencing analysis of the mgrB gene in the mutant to identify genetic alterations.
- Cloning of the wild-type mgrB gene and complementation assays using recombinant plasmids.
Main Results:
- Sequencing revealed a nucleotide deletion in the mgrB gene of Eh22-Mut, resulting in a truncated protein.
- Complementation assays with wild-type mgrB restored colistin susceptibility in the resistant mutant.
- This demonstrates that mgrB gene expression is essential for acquired colistin resistance in ECC.
Conclusions:
- The mgrB gene, a negative regulator of the PhoP/PhoQ system, is directly implicated in acquired colistin resistance in ECC cluster C-VIII.
- Mutations leading to mgrB dysfunction confer colistin resistance.
- Targeting mgrB could offer new therapeutic strategies against multidrug-resistant ECC infections.
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