Interplay of OpdP Porin and Chromosomal Carbapenemases in the Determination of Carbapenem Resistance/Susceptibility in Pseudomonas aeruginosa

High level non-carbapenemase carbapenem resistance by overlaying mutations of mexR, oprD, and ftsI in Pseudomonas aeruginosa

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is a global threat, but the mechanism of non-carbapenemase carbapenem resistance is still unclear. In the current study, we investigated the contributions of point mutations in mexR, oprD, and ftsI to carbapenem resistance in P. aeruginosa during in vivo evolution studies with consecutive clinical isolates. Real-time qPCR and Electrophoretic Mobility Shift Assay demonstrated that MexR (Gln55Pro) mutation increased MexAB efflux pump genes expression by altering MexR's binding capacity, leading to a four- to eight-fold increase in meropenem MIC in the Pae d1 Green ∆mexR and PAO1∆mexR mutants. The OprD (Trp415*) truncation affected porin structure, and the constructed mutant Pae d1 Green oprD Trp415* increased meropenem MIC by 16-fold (from 0.25 to 4 µg/mL). The contribution of ftsI mutation to meropenem resistance was confirmed by clinical linkage analysis and was estimated to cause a two-fold increase in meropenem MIC by comparing the resistant clinical isolate with the Pae d1 Green oprD Trp415*∆mexR double mutant. The study found that the oprD Trp415* allele alone accounts for the imipenem MIC in clinical isolates, while the ∆mexR and ftsI Arg504Cys alleles do not contribute to imipenem resistance. In conclusion, we identified and explored the contributions of mexR, oprD, and ftsI mutations to high level non-carbapenemase carbapenem resistance in P. aeruginosa. These findings highlight the interplay of different mutations in causing non-carbapenemase carbapenem-resistance in P. aeruginosa.

IMPORTANCE

The emergence of carbapenem-resistant Pseudomonas aeruginosa (CRPA) poses a significant global health threat, complicating treatment options for infections caused by this pathogen. Understanding the mechanisms behind non-carbapenemase carbapenem resistance is critical for developing effective therapeutic strategies. This study provides crucial insights into how specific point mutations in key genes-mexR, oprD, and ftsI-contribute to carbapenem resistance, particularly the MexR (Gln55Pro) mutation's effect on efflux pump expression and the OprD (Trp415*) truncation's impact on porin structure. The findings elucidate the complex interplay of these mutations, highlighting their roles in conferring high-level resistance, and underscore the imperative for continued research to inform therapeutic strategies against CRPA infections.

AmpC induction by imipenem in Pseudomonas aeruginosa occurs in the absence of OprD and impacts imipenem/relebactam susceptibility

In the United States, carbapenem resistance in Pseudomonas aeruginosa is linked to the regulation of chromosomal resistance determinants, AmpC and OprD. The β-lactamase AmpC requires overexpression and genetic modifications to be capable of inhibiting imipenem activity. The outer membrane porin OprD can be downregulated or undergo genetic modifications that strongly correlate with imipenem non-susceptibility. Co-administration of imipenem and the β-lactamase inhibitor, relebactam, can lower imipenem minimal inhibitory concentrations and restore susceptibility. However, it is not understood how this occurs in P. aeruginosa isolates that do not overproduce AmpC or produce a functional OprD for imipenem entry. Therefore, we investigated whether imipenem could enter P. aeruginosa in the absence of OprD and whether any of the chromosomal β-lactamases (AmpC, OXA-50, and PIB-1) contributed to imipenem and/or imipenem/relebactam non-susceptibility. This investigation evaluated 17 imipenem non-susceptible clinical isolates and three laboratory strains of PAO1, two of which were porin transposon mutants for either oprD or opdP. Expression of OXA-50 and PIB-1 RNA was similar to PAO1. However, all 20 isolates exhibited blaampC induction under sublethal exposure to imipenem. This occurred in the absence of detectable OprD protein in 18 isolates. Collectively, our data identify that (i) OprD was not the only channel required for imipenem entry and (ii) imipenem susceptibility can be restored by imipenem/relebactam due to the interaction between relebactam and blaampC overexpression due to imipenem induction.IMPORTANCEInfections caused by Pseudomonas aeruginosa are associated with high mortality and worsened clinical outcomes. The carbapenem, imipenem, has been combined with the β-lactamase inhibitor relebactam to treat carbapenem-resistant P. aeruginosa. Downregulation of the outer membrane porin, OprD is the major mechanism of imipenem resistance; however, relebactam inhibits the chromosomally encoded AmpC β-lactamase. We investigated how relebactam was able to reduce P. aeruginosa imipenem minimal inhibitory concentrations (MICs) in isolates in which OprD was downregulated. Our data show that imipenem is capable of entering the cell in the absence of OprD and capable of inducing the AmpC β-lactamase. The induction of AmpC provides a substrate for relebactam, impacting the imipenem MIC. The data presented support the use of an alternative porin(s) for entry of imipenem. This study provides the basis for further investigation into modifications of imipenem or similar molecules that would increase the affinity for other porins in isolates resistant to imipenem.

Molecular epidemiology and carbapenem resistance mechanisms of Pseudomonas aeruginosa isolated from a hospital in Fujian, China

The worldwide spread of Pseudomonas aeruginosa, especially carbapenem-resistant P. aeruginosa (CRPA), poses a serious threat to global public health. In this research, we collected and studied the clinical prevalence, molecular epidemiology, and resistance mechanisms of CRPA in Fujian, China. Among 167 non-duplicated P. aeruginosa isolates collected during 2019-2021, strains from respiratory specimens and wound secretions of older males in the intensive care unit dominated. Ninety-eight isolates (58.7 %) were resistant to at least one tested antibiotic, among which 70 strains were carbapenem-resistant. Moleclar typing of the CRPA isolates revealed they were highly divergent, belonging to 46 different sequence types. It is noteworthy that two previously reported high risk clones, ST1971 specific to China and the globally prevalent ST357, were found. Several carbapenem resistance-related characteristics were also explored in 70 CRPA isolates. Firstly, carbapenemase was phenotypically positive in 22.9 % of CRPA, genetically predominant by metallo-β-lactamase (MBL) and co-carrige of different carbapenemase genes. Then, mutations of the carbapenem-specific porins oprD and opdP were commonly observed, with frequencies of 97.1% and 100.0%, respectively. Furthermore, the biofilm formation and relative transcription levels of 8 multidrug efflux pump genes were also found to be increased in 48.6 % and 72.9 % of CRPA isolates compared to the reference strain PAO1. These findings will help fill the data gaps in molecular characteristics of CRPA on the southeastern coast of China and emphasize the urgent need for data-based specific stewardship for antipseudomonal practices to prevent the dissemination of CRPA.

Molecular characterization of carbapenem-resistance in Gram-negative isolates obtained from clinical samples at Jimma Medical Center, Ethiopia

Background

In resource-constrained settings, limited antibiotic options make treating carbapenem-resistant bacterial infections difficult for healthcare providers. This study aimed to assess carbapenemase expression in Gram-negative bacteria isolated from clinical samples in Jimma, Ethiopia.

Methods

A cross-sectional study was conducted to assess carbapenemase expression in Gram-negative bacteria isolated from patients attending Jimma Medical Center. Totally, 846 Gram-negative bacteria were isolated and identified using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Phenotypic antibiotic resistance patterns were determined using the Kirby-Bauer disk diffusion method and Etest strips. Extended-spectrum β-lactamase phenotype was determined using MAST disks, and carbapenemases were characterized using multiplex polymerase chain reactions (PCR).

Results

Among the isolates, 19% (157/846) showed phenotypic resistance to carbapenem antibiotics. PCR analysis revealed that at least one carbapenemase gene was detected in 69% (107/155) of these strains. The most frequently detected acquired genes were blaNDM in 35% (37/107), blaVIM in 24% (26/107), and blaKPC42 in 13% (14/107) of the isolates. Coexistence of two or more acquired genes was observed in 31% (33/107) of the isolates. The most common coexisting acquired genes were blaNDM + blaOXA-23, detected in 24% (8/33) of these isolates. No carbapenemase-encoding genes could be detected in 31% (48/155) of carbapenem-resistant isolates, with P. aeruginosa accounting for 85% (41/48) thereof.

Conclusion

This study revealed high and incremental rates of carbapenem-resistant bacteria in clinical samples with various carbapenemase-encoding genes. This imposes a severe challenge to effective patient care in the context of already limited treatment options against Gram-negative bacterial infections in resource-constrained settings.

Diagnosis and Therapeutic Strategies Based on Nucleic Acid Aptamers Selected against Pseudomonas aeruginosa: The Challenge of Cystic Fibrosis

Antimicrobial resistance (AMR) is a rapidly spreading global health problem, and approximately five million deaths associated with AMR pathogens were identified prior to the COVID-19 pandemic. Pseudomonas aeruginosa has developed increasing AMR, and in patients with cystic fibrosis (CF) colonized by this bacterium, rare phenotypes have emerged that complicate the diagnosis and treatment of the hosts, in addition to multiple associated "epidemic strains" with high morbidities and mortalities. The conjugation of aptamers with fluorochromes or nanostructures has allowed the design of new identification strategies for Pseudomonas aeruginosa with detection limits of up to 1 cell ⋅ mL-1 , and the synergy of aptamers with antibiotics, antimicrobial peptides and nanostructures has exhibited promising therapeutic qualities. Some selected aptamers against this bacterium have shown intrinsic antimicrobial activity. However, these aptamers have been poorly evaluated in clinical isolates and have shown decreased interactions for CF isolates, demonstrating, in these cases, uncommon phenotypes resulting from the selective qualities of this disease as well as the great adaptive capacity of the pathogen. Therefore, finding an aptamer or set of aptamers that have the ability to recognize strange phenotypes of this bacillus is crucial in the battle against AMR.

Evaluated gene expressions of Metallo beta lactamase genes GIM and , VIM, SPM in Pseudomonas aeruginosa clinical isolates

Pseudomonas aeruginosa is considered as one of the human health care problems, P. aeruginosa's carbapenem resistance emerges by several different mechanisms, some of which include carbapenems genes. P. aeruginosa's carbapenem resistance is a significant health concern, So this study aims to evaluate MBL gene expressions. The study was conducted at the Department of Microbiology, AL-Mahmoodia Hospital, over one year from January to December 2022. The samples were collected from patients with different clinical sources (Burn, Urine, Wound, Sputum, Ear, and Blood), from different ages while. Samples were collected from three hospitals in Baghdad including Al-Yarmouk Teaching Hospital, AL-Mahmmodiya Hospital, and Child's Central Teaching Hospital. A study analyzed 55 P. aeruginosa strains from various clinical sources, the study utilizes the chemical characterization, VITEK 2 system, 16s rRNA, antibiogram sensitivity tests, antibiotic susceptibility using eight antibiotics, including Amikacin, Ciprofloxacin, Levofloxacin, Imipenem Meropenem, Piperacillin, Cefepim and Aztreonam. The test of bacterial susceptibility revealed that each isolate was highly resistant to piperacillin, which are 96.36%, and lower resistance to Ciprofloxacin, which are 32%. Phenotypic screening carbapenem resistance methods combined the disk synergy test and conventional PCR that were used to detect isolates by using 16 S rRNA. This proves that the bacteria is P. aeruginosa and computed by measuring gene expression of the target genes (GIM, VIM, SPM) by using the real-time PCR, which is employed for twenty-five isolates. The result indicates that the expression level of the VIM gene is highly regulated in carbapenem-resistance isolates compared to control isolates that is 1.00. While the expression level of gene GIM and SPM is downregulated in carbapenem-resistance isolates compared to control isolates that is 6. The carbapenem VIM and GIM, SPM (class B) genes are essential for resistance in P. aeruginosa induced by chromosomal changes that modify membrane permeability efflux pump overexpression for genes. As a result, many studies require for discovering new strategies to reduce the threat to public health through preventing the spread of these isolates via tight infections, control measures, and the reduction of the danger to public health.

Role of Relebactam in the Antibiotic Resistance Acquisition in Pseudomonas aeruginosa: In Vitro Study

BACKGROUND

Pseudomonas aeruginosa shows resistance to several antibiotics and often develops such resistance during patient treatment.

OBJECTIVE

Develop an in vitro model, using clinical isolates of P. aeruginosa, to compare the ability of the imipenem and imipenem/relebactam to generate resistant mutants to imipenem and to other antibiotics. Perform a genotypic analysis to detect how the selective pressure changes their genomes.

METHODS

The antibiotics resistance was studied by microdilution assays and e-test, and the genotypic study was performed by NGS.

RESULTS

The isolates acquired resistance to imipenem in an average of 6 days, and to imipenem/relebactam in 12 days (p value = 0.004). After 30 days of exposure, 75% of the isolates reached a MIC > 64 mg/L for imipenem and 37.5% for imipenem/relebactam (p value = 0.077). The 37.5% and the 12.5% imipenem/relebactam mutants developed resistance to piperacillin/tazobactam and ceftazidime, respectively, while the 87.5% and 37.5% of the imipenem mutants showed resistance to these drugs (p value = 0.003, p value = 0.015). The main biological processes altered by the SNPs were the glycosylation pathway, transcriptional regulation, histidine kinase response, porins, and efflux pumps.

DISCUSSION

The addition of relebactam delays the generation of resistance to imipenem and limits the cross-resistance to other beta-lactams. The clinical relevance of this phenomenon, which has the limitation that it has been performed in vitro, should be evaluated by stewardship programs in clinical practice, as it could be useful in controlling multi-drug resistance in P. aeruginosa.

Comparison of Lateral Flow Immunochromatography and Phenotypic Assays to PCR for the Detection of Carbapenemase-Producing Gram-Negative Bacteria, a Multicenter Experience in Mexico

The identification of carbapenemase-producing Enterobacterales and Pseudomonas aeruginosa is important for treating and controlling hospital infections. The recommended methods for their identification require a long waiting time, technical training, and expertise. Lateral flow immunoassays such as NG-Test CARBA 5^® overcome these needs. We analyzed 84 clinical isolates of carbapenem-resistant Enterobacterales and P. aeruginosa from four different hospitals in a two-year period. Antimicrobial resistance patterns were confirmed with the broth dilution method. Evaluation of KPC, VIM, NDM, IMP, and OXA-48-like enzymes was performed and compared to NG-Test CARBA 5 and phenotypic assays. Enterobacterales represented 69% of isolates and P. aeruginosa represented 31%. Carbapenemase-producing strains were 51 (88%) of Enterobacterales and 23 (88.4%) of P. aeruginosa; 20 (34%) and 23 (88%) were Class B ß-lactamases, respectively. The NG-Test CARBA 5^® assay for Enterobacterales showed high sensitivity (98%), specificity (100%), and PPV (100%); however, it did not for P. aeruginosa. The Kappa concordance coefficient was 0.92 for Enterobacterales and 0.52 for P. aeruginosa. NG-Test CARBA 5^® is a fast and easy-to-use assay. In Enterobacterales, we found excellent agreement in our comparison with molecular tests. Despite the low agreement in P. aeruginosa, we suggest that this test could be used as a complementary tool.

Relationships between Efflux Pumps and Emergence of Heteroresistance: A Comprehensive Study on the Current Findings

Heteroresiatnce (HR) is the type of resistance toward one or more antibiotics appearing as a population of the bacterial load consisting of one or more subpopulations with lower antibiotic susceptibility levels than others. Due to the lack of appropriate diagnosis of HR isolates and their importance in resistance emergence to antibiotics, investigating the origins, emergence factors, and HR inhibitors is critical in combating antibiotic resistance. Efflux pumps (EPs) are bacterial systems that own an influential role in acquiring resistance toward anti-bacterial compounds. Studies on EPs revealed that they can affect HR emergence mechanisms and are competent to be introduced as a suitable bacterial target for diagnostic and therapeutic development in combating HR isolates. This review will consider the relations between EPs and the emergence of HR isolates and discuss their importance in confronting this type of antibiotic resistance.

Resistance Is Not Futile: The Role of Quorum Sensing Plasticity in Pseudomonas aeruginosa Infections and Its Link to Intrinsic Mechanisms of Antibiotic Resistance

Bacteria use a cell-cell communication process called quorum sensing (QS) to orchestrate collective behaviors. QS relies on the group-wide detection of extracellular signal molecules called autoinducers (AI). Quorum sensing is required for virulence and biofilm formation in the human pathogen Pseudomonas aeruginosa. In P. aeruginosa, LasR and RhlR are homologous LuxR-type soluble transcription factor receptors that bind their cognate AIs and activate the expression of genes encoding functions required for virulence and biofilm formation. While some bacterial signal transduction pathways follow a linear circuit, as phosphoryl groups are passed from one carrier protein to another ultimately resulting in up- or down-regulation of target genes, the QS system in P. aeruginosa is a dense network of receptors and regulators with interconnecting regulatory systems and outputs. Once activated, it is not understood how LasR and RhlR establish their signaling hierarchy, nor is it clear how these pathway connections are regulated, resulting in chronic infection. Here, we reviewed the mechanisms of QS progression as it relates to bacterial pathogenesis and antimicrobial resistance and tolerance.