Mobilization of bla VIM genes via the Tn6292 transposon among carbapenem-resistant Enterobacter cloacae complex isolates from colonized patients in a Spanish hospital

The aim of this study was to perform molecular characterization of the carbapenem-resistant Enterobacter cloacae complex (ECC) isolates from colonized patients in a hospital using whole-genome sequencing (WGS) technology. As part of routine surveillance for multidrug-resistant bacterial colonization, 21 ECC isolates were recovered from patients at San Carlos Hospital in Madrid (Spain) between December 2020 and November 2024. WGS was used to determine their genetic relatedness. Furthermore, species identification, sequence type (ST), resistome, plasmid content, and flanking mobile genetic elements (MGEs) of the carbapenemase genes were derived from the WGS data. The most prevalent carbapenemase gene identified was bla VIM-1 ( n = 18, 85.7%), with other notable genes including bla KPC-2 ( n = 1, 4.8%), bla KPC-3 ( n = 1, 4.8%), and bla OXA-48 ( n = 1, 4.8%). Several bla ACT and bla ESBL variants were also found among the carbapenem-resistant ECC isolates. All of them carried at least one bla ACT gene, with bla ACT-7 (11/21) and bla TEM -type (14/21) genes being the most common AmpC and ESBL-encoding genes, respectively. Additionally, two isolates exhibited the presence of the mcr-9 gene. Overall, E. hormaechei subsp. steigerwaltii (ST93), followed by E. hormaechei subsp. hoffmanii (ST78 and ST50), were the predominant species and STs circulating among the carbapenem-resistant ECC strains. The bla VIM-1 gene was part of class 1 integrons located within a Tn3-family transposon, Tn6292. bla KPC and bla OXA-48 were linked to Tn4401 and Tn1999 transposons, respectively. In conclusion, the presence of the bla VIM within a transposon Tn6292 enhances its mobility across bacterial genomes, underscoring the value of high-throughput sequencing in monitoring the spread of carbapenem-resistant ECC isolates. IMPORTANCE This study highlights why monitoring the spread of antibiotic-resistant bacteria in hospitals is critical. By analyzing the complete DNA of carbapenem-resistant bacteria, antibiotics were considered a last line of treatment. We found that the resistance genes are not isolated. Instead, they are embedded within mobile elements called transposons. This means that they can “jump” between different bacteria, accelerating the spread of resistance. These findings emphasize the importance of high-resolution genomic technologies to track and control the spread of these dangerous bacteria in clinical settings, helping preserve the effectiveness of life-saving treatments.