Report and Comparative Genomics of an NDM-5-Producing Escherichia coli in a Portuguese Hospital: Complex Class 1 Integrons as Important Players in bla_NDM Spread

New Delhi metallo-beta-lactamase (NDM) has been spreading across the globe, but the causes of its success are poorly understood. We characterized a bla_NDM-5-positive Escherichia coli strain from a Portuguese hospital and conducted comparative genomic analyses to understand the role of clonal background and horizontal gene transfer in bla_NDM-5 dissemination.

After bla_NDM PCR screening and genome sequencing, Ec355340 was subjected to mating, transformation, and plasmid curing assays and MICs determination for several antibiotics. Comparison with data compiled from public databases was performed.

bla_NDM-5 was in a complex integron co-located in a FIB-FII plasmid (pEc355340_NDM-5). The mating assays were unsuccessful, but plasmid transformation into a susceptible host led to resistance to all beta-lactams and to sulfamethoxazole-trimethoprim. The profile of virulence genes (n = 73) was compatible with extraintestinal pathogenesis. An analysis of genomes from public databases suggested that bla_NDM-5 has rarely been associated with ST156 strains (such as Ec355340), while is has frequently been found on strains of the ST10 clonal complex. However, ST156 may play a role in the co-spreading of bla_NDM and mcr genes. Regardless, comparative genomics confirmed the presence of bla_NDM in similar complex integrons in plasmids (48/100 plasmids most similar to pEc355340_NDM-5) and ST156 genomes (20/41 bla_NDM-positive genomes).

bla_NDM-5 and other bla_NDM variants were more frequently associated to complex integrons than previously reported and, therefore, these platforms may be important drivers in their dissemination. The identification of bla_NDM-5 for the first time in Portugal could be a game-changer in the current Portuguese antibiotic resistance scenario, as this gene encodes a higher-level resistance phenotype, and its spread may be facilitated due to the association with complex integrons.