Bacterial characteristics of carbapenem-resistant Enterobacteriaceae (CRE) colonized strains and their correlation with subsequent infection

Abstract

Background: Searching the risk factors for carbapenem-resistant Enterobacteriaceae (CRE) infection is important in clinical practice. In the present study, we aim to investigate bacterial characteristics of colonizing strains and their correlation with subsequent CRE infection.

Methods: Between May 2018 and January 2019, patients hospitalized in the department of haematology and intensive care unit (ICU) were screened for CRE by rectal swabs and monitored for the outcome of infection. We identified the species and carbapenemase-encoding genes of colonizing strains and performed antimicrobial susceptibility tests and multilocus sequence typing (MLST). Risk factors for subsequent CRE infections were ascertained by univariate and multivariable analysis.

Results: We collected a total of 219 colonizing strains from 153 patients. Klebsiella pneumoniae was the most abundant species, and MLST analysis showed rich diversity. K. pneumoniae carbapenemase (KPC) was predominant in the infection group (72.4%). In the non-infection group, 35.4% of strains were non-carbapenemase-producing CRE (NCP-CRE), and New Delhi metallo-β-lactamase (NDM) was predominant (42.2%). The rate of high-level carbapenem resistance (minimum inhibitory concentration [MIC] ≥ 64 mg/L for meropenem and ertapenem, ≥ 32 mg/L for imipenem) was remarkably higher in the infection group than in the non-infection group (P < 0.001). Univariate analysis showed that K. pneumoniae, high-level carbapenem resistance, CP-CRE and KPC-CRE were infection risk factors after CRE colonization. On multivariable analysis with different carbapenemase dichotomizations, KPC-CRE (adjusted odds ratio [aOR], 4.507; 95% confidence interval [CI], 1.339-15.171; P = 0.015) or imipenem MIC ≥ 32 mg/L (aOR, 9.515; 95% CI, 1.617-55.977; P = 0.013) were respectively identified as independent risk factors for subsequent infection.

Conclusions: Patients colonized with KPC-CRE or strains with an imipenem MIC ≥ 32 mg/L were at particularly high risk of subsequent CRE infections during their hospital stay.

Keywords: Bacterial characteristic; Carbapenem-resistant Enterobacteriaceae; Intestinal colonization; Risk factor.

Fig. 1

The distribution of minimum inhibitory concentrations (MICs) of carbapenem (meropenem, imipenem and ertapenem) in different groups of carbapenem-resistant Enterobacteriaceae colonizing strains. A Meropenem MIC distribution in the infection group (n = 58). B Meropenem MIC distribution in the non-infection group (n = 161). C Imipenem MIC distribution in the infection group. D Imipenem MIC distribution in the non-infection group. (E) Ertapenem MIC distribution in the infection group. (F) Ertapenem MIC distribution in the non-infection group

Fig. 2

The distribution of species and carbapenem MICs among CRE-colonizing strains producing different carbapenemases. A Species distribution among strains producing different carbapenemases. B Carbapenem MICs distribution among KPC-producing strains (n = 71). C Carbapenem MIC distribution among strains producing other carbapenemases (n = 84). D Carbapenem MIC distribution among NCP-CRE strains (n = 64). Abbreviations: MEM, meropenem; IPM, imipenem; ETP, ertapenem; MIC, minimum inhibitory concentration; CRE, carbapenem-resistant Enterobacteriaceae; KPC, K. pneumoniae carbapenemase; NCP-CRE, non-carbapenemase-producing CRE