Novel E. coli ST5123 Containing blaNDM-1 Carried by IncF Plasmid Isolated from a Pediatric Patient in Serbia

Katarina Novovic, Zorica Vasiljevic, Milos Kuzmanovic, Jelena Lozo, Jelena Begovic, Milan Kojic, Branko Jovcic

New Delhi metallo-β-lactamase (NDM) is a serious challenge to the treatment of infections and public health. Serbia has been designated as an endemic region for isolates carrying the blaNDM-1 gene, as well as one of several commonly proposed countries of origin. This is the first report of NDM-1-positive Escherichia coli from Serbia. A carbapenem-resistant clinical isolate of E. coli strain IMD989, isolated from the blood culture of a pediatric patient with leukemia, was subjected to antimicrobial susceptibility tests, molecular typing, and conjugation experiments. The strain exhibited resistance to meropenem and was classified as a novel sequence type, ST5123, belonging to E. coli phylogenetic group A. ST5123 showed similarity to veterinary isolates ST93 and ST3977. The blaNDM-1 gene was detected by polymerase chain reaction (PCR) and sequencing. Cloning and sequencing of genomic clones confirmed that strain IMD989 produces an NDM-1 variant. Conjugation experiments, pulsed-field gel electrophoresis, and Southern blot hybridization revealed that blaNDM-1 was located in IMD989 on a transmissible 80 kb plasmid, designated as pIMD989. PCR analysis confirmed that pIMD989 belongs to the IncF plasmid family. Propagation of IMD989 and selected transconjugants carrying pIMD989 over 14 days in solid media with and without antibiotic selection showed that pIMD989 is a stable plasmid.