Low prevalence of mobilized resistance genes blaNDM, mcr-1, and tet(X4) in Escherichia coli from a hospital in China

Abstract

The emergence and spread of carbapenemase genes, colistin resistance genes mcr-1, and tigecycline resistance gene tet(X) represent a significant threat to clinical therapy and public health. In this study, we investigated the presence of carbapenemase genes, mcr-1, and tet(X) in 298 Escherichia coli strains obtained from a teaching hospital in China. In total, eight (2.68%), six (2.01%), and one (0.34%) E. coli isolates carried blaNDM, mcr-1, and tet(X4), respectively. The blaNDM gene was located on IncX3 (n = 4), F2:A-:B- (n = 3), and F2:A1:B1 (n = 1) plasmids, with high similarity to multiple plasmids belonging to the same incompatibility type from Enterobacteriaceae. Six MCR-producing strains contained mcr-1-carrying IncI2 plasmids, organized similarly to other mcr-1-bearing IncI2 plasmids from animals in China. The blaCTX−M−55/64/132/199 gene located within a typical transposition unit (ISEcp1-blaCTX−M-orf477Δ) was inserted near dnaJ to generate 5-bp direct repeats in four mcr-1-positive plasmids. The tet(X) and another four resistance genes [aadA2, tet(A), floR, and Δlnu(F)] were co-located on an IncX1 plasmid, highly similar to other tet(X4)-carrying IncX1 plasmids from Escherichia and Klebsiella of animal or food origin, except that the conjugative transfer region of IncX1 plasmids was absent in our plasmid. Although a low prevalence of blaNDM, mcr-1, and tet(X) was observed in E. coli from patients in this study, their dissemination associated with some successful pandemic plasmids is of great concern. The continued surveillance of these crucial resistance genes in patients should be strengthened.

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“…However, it is imperative to acknowledge that the number of isolates from these sources was relatively limited, posing a constraint on our study. Currently, tet(X4) is commonly detected in E. coli originating from food-producing animals and food products, particularly pigs and pork, but it is infrequently reported in E. coli from humans (He et al, 2019;Sun et al, 2019aSun et al, , 2020Dong et al, 2022;Li et al, 2021a;Sun et al, 2023). The detection rate of tet(X4) in this study was relatively low (0.65%), aligning closely with the findings of Sun et al (0.22%) (Sun et al, 2019a), Yu et al (0.17%) (Yu et al, 2022), and Zhang et al (0.32%) (Zhang et al, 2020) in their research on E. coli collected from China.…”

“…(Figure 1C). However, pYUYZPE244-2 as well as plasmids pDW28-tet(X4), pRF45-1_31k_tetX and pYUXYEH3934-2 lacked the conjugative transfer region of IncX1 plasmids (Figure 1C), potentially explaining their failure in conjugation (Sun et al, 2023).…”