First report of IMP-1 in a clinical isolate of Escherichia coli in Latin America

To the Editor—The emergence of carbapenem-resistant Enterobacterales (CRE) is a matter of public health concern that seriously compromises antibiotic treatment for severe infections. Since the first report of acquired IMP-1 in Pseudomonas aeruginosa in Japan in 1988,¹ genes encoding IMP enzymes have spread rapidly among Acinetobacter spp and Enterobacterales.² Here, we describe the characteristics of a clinical isolate of E. coli harboring bla _IMP-1 gene in Latin America.

An Escherichia coli (termed E. coli 7469F) was recovered from the blood of a patient at Hospital de Clínicas de Porto Alegre in Southern Brazil in May 2019. The E. coli 7469F was not susceptible in vitro to meropenem and ertapenem by the disk-diffusion method. The presence of carbapenemase genes (bla _NDM-1, bla _KPC-2, bla _VIM-type, bla _GES-type, bla _OXA-48-like, and bla _IMP-type) was evaluated using multiplex high-resolution melting (HRM) real-time polymerase chain reaction (PCR),³ which yielded a positive result only for the bla _IMP-type gene. The clinical isolate was submitted to conjugation experiment using E. coli J53 as a receptor, and 1 transconjugant (T7469F) was selected for further analysis. The minimal inhibitory concentrations (MICs) of antibiotics representative of β-lactams, aminoglycosides, glycilcycline, and chloramphenicol were evaluated by broth microdilution for the E. coli 7469F and its transconjugant (T7469F). The transconjugant T7469F presented significant increase in MICs of the carbapenems and ceftazidime compared with E. coli J53 (Table 1). T7469F did not present an increased MIC for aminoglycosides, chloramphenicol, or tigecycline. This whole-genome shotgun project has been deposited at DDBJ/ENA/GenBank under the accession WTVT00000000. The version described here is version WTVT01000000.

Table 1. Minimal Inhibitory Concentrations (MICs) of Several Antibiotics Used to Treat Escherichia coli 7469F, Transconjugant 7469F, and E. coli J53

The whole genomes of the clinical isolate and its transconjugant were sequenced using the MiSeq platform (Illumina, San Diego, CA), and the data were analyzed using the following tools from the Centre for Genomic Epidemiology website (http://www.genomicepidemiology.org): MLST to characterize sequence typing (ST), ResFinder to characterize antibiotic resistance mechanisms, and PlasmidFinder to characterize plasmid types. Analyses of the whole-genome sequencing (WGS) data confirmed the presence of the bla _IMP-1 gene in isolate 7469F and its transconjugant. Other genes related to resistance to β-lactam (bla _CTX-M-15 and bla _OXA-1) were found in the clinical isolate using in silico data analyses. E. coli 7469F presented 4 plasmids, and the bla _IMP-1 gene was identified in the plasmid IncA/C₂. In silico data confirmed that the IncA/C₂ was the only plasmid identified in the transconjugant T7469F. Plasmids belonging to the IncA/C incompatibility group are broad host–range vehicles commonly identified among animal and clinical bacterial isolates of Enterobacterales worldwide. This plasmid usually harbors different resistance genes, including bla _CMY, bla _NDM, bla _VIM, and bla _IMP.⁴ The WGS analyses also indicated that the E. coli 7469F belonged to the ST648. ST648 is a predominant multidrug-resistant ST observed worldwide; it is increasingly reported in multiple regions.^5-8 In addition, several publications have reported the frequent occurrence of ST648 strains with various β-lactamases (extended-spectrum β-lactamases [ESBLs], New Delhi metallo-β-lactamases [NDMs], and Klebsiella pneumoniae carbapenemase [KPCs]),^9,10 as well as the mcr-1 gene.⁸

To the best of our knowledge, this is the first report of a clinical isolate of E. coli ST648 carrying an IncA/C₂ plasmid with the bla _IMP-1 gene in Latin America. Notably, the broad host range of IncA/C₂ plasmid may contribute to the diffusion and maintenance of bla _IMP-1 in different groups of bacteria. Considering the concerning spread of carbapenem resistance mediated by plasmids and considering the high prevalence of ST648 E. coli, our study highlights the importance of continuous surveillance studies of carbapenemase genes in Latin America.