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Porin Deficiency in Carbapenem-Resistant Enterobacter aerogenes Strains

Min Hao^1,2, Meiping Ye^1,2, Zhen Shen^1,2

¹1 Institute of Antibiotics, Huashan Hospital, Fudan University , Shanghai, People's Republic of China .

Microbial Drug Resistance (Larchmont, N.Y.)

|April 15, 2018

Abstract

Purpose:

The more frequent reports of carbapenem-resistant Enterobacteriaceae have raised the alarm for public health. Apart from the production of carbapenemases, deficiency (decreased or loss of expression) of outer membrane proteins (OMPs) has been proposed as a potentially important mechanism of carbapenem resistance. The aim of the present study was to evaluate the contribution of the major OMPs to carbapenem resistance in Enterobacter aerogenes (CREA) isolates and also investigate the role of small RNAs (sRNAs) in inducing porin-associated permeability defects.

Materials And Methods:

The differential expression of OMPs was analyzed in four clinical CREA isolates. omp35 and omp36 genes were further investigated by whole-genome sequencing, induction of meropenem resistance, sRNA overexpression, OMP complementation assays, and reverse transcription-quantitative PCR.

Results:

All four isolates examined were deficient in omp35 and omp36. Functional restoration of these two genes confirmed their contribution to carbapenem resistance. The meropenem induction assay further revealed that porin deficiency plays a role in carbapenem resistance under antibiotic selection pressure. Single-point mutations in omp36 leading to premature stop codons were detected in two of the isolates. Elevated expression levels of the sRNAs micF and micC were detected in the other two porin-deficient isolates, which were predicted to be potential porin regulators from whole-genome sequencing. Overexpression of micF and micC downregulated the expression of Omp35 and Omp36, respectively.

Conclusions:

Porin deficiency plays an important role in carbapenem resistance among clinical E. aerogenes isolates under regulation of the sRNAs micC and micF. Furthermore, overexpression of micC and micF had a minor to no impact on carbapenem minimum inhibitory concentrations, and thus, the regulatory mechanism is likely to be complex.

Insights

Outer membrane protein deficiency in Enterobacter aerogenes contributes to carbapenem resistance. Small RNAs micF and micC regulate this process, though the exact mechanism remains complex.

Area of Science:

Microbiology
Molecular Biology
Genetics

Background:

Carbapenem-resistant Enterobacteriaceae (CRE) pose a significant public health threat.
Outer membrane protein (OMP) deficiency is an emerging mechanism of carbapenem resistance.
Enterobacter aerogenes is a relevant pathogen in this context.

Purpose of the Study:

To determine the role of major OMPs in carbapenem resistance in E. aerogenes.
To investigate the involvement of small RNAs (sRNAs) in OMP-mediated carbapenem resistance.
To analyze OMP expression and genetic mutations in clinical carbapenem-resistant E. aerogenes (CREA) isolates.

Main Methods:

Analysis of OMP differential expression in clinical CREA isolates.
Whole-genome sequencing and gene-specific analysis (omp35, omp36).
Meropenem induction assays, sRNA overexpression, OMP complementation, and RT-qPCR.

Main Results:

All four CREA isolates showed deficiency in omp35 and omp36, confirmed by functional restoration.
Meropenem induction demonstrated porin deficiency's role under antibiotic pressure.
Mutations in omp36 and elevated expression of micF and micC sRNAs were observed, with sRNAs downregulating OMP expression.

Conclusions:

Porin deficiency, specifically of Omp35 and Omp36, is a key factor in carbapenem resistance in E. aerogenes.
The sRNAs micF and micC regulate this porin deficiency.
The overall regulatory mechanism influencing carbapenem resistance is complex and requires further investigation.

Read full analysis

Keywords:

Enterobacter aerogenes carbapenem induction carbapenem resistance outer membrane proteins small RNA

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