 This study examined five Citrobacter freundi strains isolated from the same patient, which displayed different phenotypic characteristics despite producing the KPC enzyme. These strains were found to contain an additional gene cassette, including BlarCarb2 and II, AADA2, DFI19, CATB3, CMLA1, MPH, E, MSRE, and QNI1, which explained their differences in phenotype. Additionally, the presence of these genes allowed the strains to evade detection by phenotypic methods and acquire and transfer-resistant gene cassettes. This highlights the need for more accurate diagnostic tools to identify and treat these bacteria. This article was authored by Stephen M. Brecher, Isabella Atichola, and Fred C. Tenover.