Genomic analysis of VIM-2-producing Enterobacter hormaechei subsp. steigerwaltii

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• Carbapenemase-producing Enterobacterales (CPE) pose a significant global health threat due to antimicrobial resistance.
• Enterobacter hormaechei is an opportunistic pathogen that can harbor resistance genes.
• The VIM-2 carbapenemase is a critical determinant of resistance to carbapenem antibiotics.

Purpose of the Study:

• To investigate the occurrence and genetic context of the blaVIM-2 gene in Enterobacter hormaechei isolates.
• To characterize the plasmids and transposons carrying blaVIM-2.
• To explore the reasons for phenotypic variation in carbapenemase activity among CPE isolates.

Main Methods:

• Whole-genome sequencing of Enterobacter hormaechei isolates.
• Plasmid analysis and characterization.
• Identification of transposons and integrons.
• Antimicrobial susceptibility testing and phenotypic carbapenemase detection (Carba NP test).
• Analysis of genetic mutations in resistant strains.

Main Results:

• The blaVIM-2 gene was found within the Tn1332 transposon, integrated into a class 1 integron remnant on a conjugative plasmid.
• Three Enterobacter hormaechei subsp. steigerwaltii isolates belonging to ST90 harbored Tn1332.
• Isolate 104D2 showed phenotypic resistance despite carrying Tn1332, later found to have a WecA mutation and increased Tn1332 copy number in a resistant mutant.
• Isolates 90H2 and 90H3 also carried an IncHI plasmid with the blaCTX-M-15 ESBL gene.

Conclusions:

• This study reports the first instance of Tn1332 in Enterobacterales, highlighting its potential for dissemination.
• Genetic alterations, such as mutations in WecA and changes in transposon copy number, can influence the phenotypic expression of carbapenemase activity.
• The findings underscore the complex mechanisms underlying antimicrobial resistance in CPE and the importance of detailed molecular characterization.