Emergence of IncFIA Plasmid-Carrying blaNDM-1 Among Klebsiella pneumoniae and Enterobacter cloacae Isolates in a Tertiary Referral Hospital in Mexico

The emergence of New Delhi metallo-β-lactamase 1 on carbapenemase-producing bacteria has raised a major worldwide public health concern. This study reports the dissemination of bla NDM-1 in carbapenem-resistant isolates that caused nosocomial infections in a tertiary hospital in Mexico City. Seven Enterobacter cloacae and three Klebsiella pneumoniae nosocomial isolates from the same time period harbored the bla NDM-1 gene. The resistance phenotype and the bla NDM-1 gene were transferred through conjugative plasmids belonging to the incompatibility group IncFIA of 85, 101, and 195 kb in E. cloacae and 95 and 101 kb in K. pneumoniae isolates. Restriction fragment length polymorphism analysis showed that bla NDM-1 was carried in similar plasmids with molecular sizes of 101 and 85 kb, each one in three isolates of E. cloacae and one of 101 kb on two isolates of K. pneumoniae . During a 9-month period, six of the seven isolates of E. cloacae analyzed harbored bla NDM-1 and belonged to clone E1. Similarly, over a 5-month period, two of the three K. pneumoniae isolates that harbored bla NDM-1 belonged to clone K1. These results demonstrate the horizontal transfer of bla NDM-1 between different bacterial species, dissemination of clones with high levels of resistance to carbapenems, and underscore the need for heightened measures to control their further spread.