Pseudomonas aeruginosa OprD-Family Porins Facilitate Imipenem Translocation Resulting in AmpC β-Lactamase Induction Contributing to the Effectiveness of Imipenem/Relebactam
type: CreativeWork
description: Background: Multidrug-resistant Pseudomonas aeruginosa is a serious concern in the United States and considered an urgent priority pathogen globally. Due to multiple chromosomal resistance factors, P. aeruginosa can emerge resistant to most available antibiotics. Carbapenem antibiotics are a last line of defense antibiotic of choice for P. aeruginosa; however, emergence of resistance has increased in hospital onset cases since 2019. The introduction of the β-lactamase inhibitor relebactam in combination with the carbapenem imipenem has restored susceptibility in some isolates, yet the mechanism remains unknown. Imipenem resistance has been tied to the depletion of the outer membrane porin, OprD and overproduction of AmpC chromosomal β-lactamase. It is not known how relebactam potentiates imipenem when AmpC levels are low, nor how imipenem traffics into the cell in the absence of OprD. The purpose of this dissertation was to address these questions using three approaches. First, determine the contribution of the chromosomal β-lactamases, AmpC, Pib-1, and OXA-50 on imipenem susceptibility. Second, determine how relebactam potentiates imipenem in the absence of OprD. Third, to determine the contribution other OccD porins: OpdP, OpdB, and OpdB in the translocation of imipenem into the cell in the absence of OprD. Method: A panel of laboratory strains of P. aeruginosa and various clinical isolates were evaluated. Methods used in this dissertation included RT-qPCR, western analysis, whole genome sequencing, RNAseq analysis and linear regression analysis. Results: Basal levels of ampC were found to contribute very little to imipenem MICs and were not an accurate predictor of the impact relebactam had on imipenem MICs. However, loss of OprD correlated with imipenem nonsusceptibility. Protein production was the strongest indicator and resolved discordant phenotypes observed in isolates when only transcript levels were taken into consideration. AmpC induction occurred upon ex…
abstract: Background: Multidrug-resistant Pseudomonas aeruginosa is a serious concern in the United States and considered an urgent priority pathogen globally. Due to multiple chromosomal resistance factors, P. aeruginosa can emerge resistant to most available antibiotics. Carbapenem antibiotics are a last line of defense antibiotic of choice for P. aeruginosa; however, emergence of resistance has increased in hospital onset cases since 2019. The introduction of the β-lactamase inhibitor relebactam in combination with the carbapenem imipenem has restored susceptibility in some isolates, yet the mechanism remains unknown. Imipenem resistance has been tied to the depletion of the outer membrane porin, OprD and overproduction of AmpC chromosomal β-lactamase. It is not known how relebactam potentiates imipenem when AmpC levels are low, nor how imipenem traffics into the cell in the absence of OprD. The purpose of this dissertation was to address these questions using three approaches. First, determine the contribution of the chromosomal β-lactamases, AmpC, Pib-1, and OXA-50 on imipenem susceptibility. Second, determine how relebactam potentiates imipenem in the absence of OprD. Third, to determine the contribution other OccD porins: OpdP, OpdB, and OpdB in the translocation of imipenem into the cell in the absence of OprD. Method: A panel of laboratory strains of P. aeruginosa and various clinical isolates were evaluated. Methods used in this dissertation included RT-qPCR, western analysis, whole genome sequencing, RNAseq analysis and linear regression analysis. Results: Basal levels of ampC were found to contribute very little to imipenem MICs and were not an accurate predictor of the impact relebactam had on imipenem MICs. However, loss of OprD correlated with imipenem nonsusceptibility. Protein production was the strongest indicator and resolved discordant phenotypes observed in isolates when only transcript levels were taken into consideration. AmpC induction occurred upon ex…
author: Freed Jr., Shawn M.
language: en_US
keywords: Beta-Lactamase, Carbapenem, Pseudomonas, Resistance
date published: 2024
date modified: 2026-07-24T01:50:57Z
provider: Creighton University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Creighton University