Emergence of a multidrug-resistant Citrobacter freundii ST8 harboring an unusual VIM-4 gene cassette in Poland

- Molecular analysis of a multidrug-resistant carbapenem-resistant Citrobacter freundii was performed, revealing the presence of the VIM-4 isoenzyme.
- The blaVIM-4 gene was inserted into an unusual gene cassette containing a 169-bp direct repeat of the 3′ segment of the blaVIM-4 gene.
- All unusual gene cassettes containing VIM-DR (direct repeat) described thus far have been harbored by non-fermenters, i.e., Acinetobacter and Pseudomonas.
- The results presented here underscore the importance of resistance determinant mobility, which may go even beyond genus, family, and order boundaries.

ObjectivesThe growing incidence of multidrug-resistant (MDR) bacteria is an emerging challenge in modern medicine. The utility of carbapenems, which are considered 'last-line' agents, is being diminished by the growing incidence of various resistance mechanisms in Gram-negative bacteria. A molecular investigation was performed of an MDR carbapenem-resistant Citrobacter freundii of sequence type 8 (ST8) isolated from a hematology patient with acute myeloid leukemia.MethodsMultilocus sequence typing and analysis of the nucleotide sequence of the class I integron were performed using PCR and Sanger sequencing. Transformation of the resistance plasmid isolated following the alkaline lysis method was performed using chemically competent E. coli TOP10.ResultsMolecular analysis of the carbapenem-resistant C. freundii revealed the presence of the VIM-4 isoenzyme located on the ∼55-kb transferable resistance plasmid. Interestingly, the blaVIM-4 gene was inserted into an unusual gene cassette containing a 169-bp direct repeat of the 3′ segment of the blaVIM-4 gene.ConclusionsAll unusual gene cassettes containing VIM-DR (direct repeat) described thus far have been harbored by non-fermenters, i.e., Acinetobacter and Pseudomonas, underscoring the importance of resistance determinant mobility, which may go even beyond genus, family, and order boundaries. Great efforts need to be taken to explore pathways of resistance to 'last-resort' antimicrobials, especially among clinically relevant pathogens.