Transmission of imipenem resistance determinants during the course of an outbreak of NDM-1 Escherichia coli in a sick newborn care unit

Objectives This study reports a cluster of septicaemic newborns with imipenem-resistant Escherichia coli in the blood and delineates the possible mechanisms of transmission of imipenem resistance with respect to the New Delhi metallo-β-lactamase (NDM-1) gene. Methods During a point prevalence survey, attempts were made to isolate Gram-negative bacilli (GNB) from the environment of a sick newborn care unit (SNCU) and body sites of neonates. Subsequently, four fresh neonates admitted to the SNCU developed sepsis with E. coli. E. coli isolates from body sites and blood of the newborns were analysed in terms of clonality, carbapenemases, integrons, virulence factors, porins and transmissibility. Results During the survey, both imipenem-resistant and imipenem-susceptible E. coli were isolated from the body sites of neonates, but none from the environment. None of these neonates developed sepsis. The freshly admitted septicaemic neonates had imipenem-resistant E. coli in their blood, which were similar to the imipenem-susceptible E. coli obtained from the body sites (during the survey) in terms of clonality, phylogroup, virulence and other resistance genes, except possession of bla NDM-1. Imipenem-resistant E. coli from blood and body sites were not clonal, though both had bla NDM-1. Besides E. coli, other GNB isolated from the environment and body sites also harboured bla NDM-1. Imipenem-resistant and imipenem-susceptible E. coli from the blood and body sites respectively, possessed a novel AmpC β-lactamase, bla CMY-59. The plasmid carrying bla NDM-1 was transferable. Conclusions The time frame of isolation and clonal identity indicated a possible transfer of bla NDM-1 from imipenem-resistant GNB to the imipenem-susceptible E. coli, which subsequently caused septicaemia. This establishes the promiscuous nature of bla NDM-1 and emphasizes the need for the early recognition of similar isolates.