Klebsiella pneumoniae is a bacterial species causing a major clinical threat due to its tendency to develop resistance to antibiotics, particularly because of its ability to acquire plasmids carrying resistance genes such as carbapenemases. When these genes are located on the same plasmid, the potential for their spread is even greater. In this study, we focused on K. pneumoniae strains isolated in Colombia, that carry an IncC plasmid harbouring three carbapenemases encoded by the blaKPC-2, blaNDM-1, and blaVIM-24 genes. These strains have been analysed in the presence of imipenem to determine whether they display a heteroresistance profile and to assess the plasmid stability in absence of antibiotic. To investigate this, E-tests, Spot PAPs (Population Analysis Profile) and full PAPs, a plasmid stability assay, a PCR, a Percoll density test, and a whole genome sequencing (WGS) followed by complementary bioinformatics analyses were performed. The results of the E-tests revealed colonies that were able to grow within the imipenem inhibition zone, suggesting a heteroresistance phenomenon, and the PAPs confirmed bacterial survival patterns consistent with a heterogeneous response to imipenem. Some selected colonies with high concentrations of imipenem showed stable resistance, while others retained the resistance profile of the original strain. Multiplex PCR and sequencing revealed that the plasmid remained stable after passages without imipenem, indicating that the phenotypic change was not due to loss of the plasmid. Genomic analyses revealed variants located in chromosomal and plasmid regions, particularly in genes associated with mobile elements. Together, our results suggest that K. pneumoniae strains exhibit a heterogeneous response to imipenem and that this response could be influenced by genetic modulations rather than by a complete loss of the plasmid.