A new mutation in mgrb mediating polymyxin resistance in Klebsiella variicola

Area of Science:

• Microbiology
• Genomics
• Antimicrobial Resistance

Background:

• Polymyxin resistance is a growing public health concern, driven by chromosomal or plasmid mechanisms.
• Alterations in the MgrB regulator are common in Klebsiella spp. but uncharacterized in Klebsiella variicola.
• Migratory birds can act as reservoirs for antimicrobial-resistant bacteria.

Purpose of the Study:

• To characterize polymyxin-resistant Klebsiella variicola isolates from migratory birds.
• To investigate the genetic mechanisms conferring polymyxin resistance in these isolates.
• To assess the role of the mgrB gene in polymyxin resistance in K. variicola.

Main Methods:

• Isolation and microbiological characterization of K. variicola from migratory bird microbiota.
• SpeI-Pulsed Field Gel Electrophoresis (PFGE) for genetic relatedness analysis.
• Broth microdilution for antimicrobial susceptibility testing.
• Whole genome sequencing (Illumina MiSeq) and bioinformatic analysis (BLAST, PROVEAN) of resistance genes and regulatory systems (PmrAB, PhoPQ, RstAB, CrrAB, MgrB).
• mgrB complementation studies to confirm functional impact.

Main Results:

• Three polymyxin-resistant K. variicola isolates (M14, M15, M50) were identified, belonging to two distinct clones.
• Deleterious mutations in the phoQ gene were found in isolates M14 and M15.
• A single deletion in the mgrB gene, resulting in a non-functional protein, was identified in isolate M50.
• Complementation with a functional mgrB gene restored polymyxin susceptibility in the M50 isolate.

Conclusions:

• A non-functional mgrB variant is confirmed to confer polymyxin resistance in Klebsiella variicola.
• This study highlights the significant role of the MgrB regulator in polymyxin resistance within K. variicola.
• Wildlife, specifically migratory birds, can harbor and disseminate novel polymyxin resistance mechanisms.