Towards understanding single-channel characteristics of OccK8 purified from Pseudomonas aeruginosa

A review of recently discovered mechanisms of cephalosporin resistance in Pseudomonas aeruginosa

Pseudomonas aeruginosa frequently causes respiratory tract infections in immunocompromised patients as well as bloodstream, urinary tract, skin, and soft tissue infections. The increasing prevalence of multidrug-resistant P. aeruginosa strains poses a significant clinical challenge. Cephalosporin antibiotics from the β-lactam class are commonly prescribed to treat infections owing to their broad spectrum of activity and generally low host toxicity. P. aeruginosa utilizes β-lactamase enzymes, efflux pumps, and mutations in outer membrane porins/transporters and target proteins, all of which confer resistance to cephalosporin antibiotics. This review categorizes resistance mechanisms into (i) well-characterized pathways, such as AmpC β-lactamase and Mex efflux pumps, (ii) recently described mutations linked to cephalosporin resistance (e.g., ygfB, sltB1, pbp3, galU, pmrAB, fusA1, and gyrA), and (iii) hypothetical β-lactamases and other mechanisms requiring further validation. A variety of β-lactamase inhibitors have been developed to overcome β-lactamase-mediated resistance, but resistance has already been observed toward inhibitors via the accumulation of mutations within the targeted β-lactamase enzyme or increased activity of efflux pumps. Understanding the regulation and pathways that lead to resistance is crucial in developing effective strategies to combat P. aeruginosa infections and extending the therapeutic lifespan of cephalosporin antibiotics.

Outer membrane permeability of Pseudomonas aeruginosa through β-lactams: new evidence on the role of OprD and OpdP porins in antibiotic resistance

Gram-negative bacteria are a major concern for public health, particularly due to the continuous rise of antibiotic resistance. A major factor that helps the development of resistance is the outer membrane that is essential since it acts as a strong permeability barrier to many antibiotics that are effective against other bacteria. In this study, we determine the specific permeability coefficients for various antibiotics in Pseudomonas aeruginosa strains, which differ from each other for their porin expressions. We showed that OprD and OpdP porins contribute both to internalize meropenem and biapenem. Using qRT-PCR, we demonstrated that their expression is dependent of the various phases of cellular growth. We were able to show how the OpdP porin is less expressed in exponential growth phases, while it tends to be produced when the bacterial culture enters into the latent phase, in an inversely proportional way compared to the OprD porin. The deletion of the OpdP porin, in the presence of meropenem at concentrations equivalent to the MIC values, contributes to the selection of carbapenem-resistant strains. Therefore, the presence of mutations/deletions of the OpdP porin should receive greater consideration from a clinical point of view as the use of meropenem at nonoptimal concentrations could lead to the appearance of resistance phenotypes.IMPORTANCECarbapenem-resistant strains of Pseudomonas aeruginosa are among the major threats to public health. The permeability of the outer membrane for the β-lactam antibiotics is one of the major factors that reduce the activity of the antibiotics. In this study, we measure the low permeability coefficient of the P. aeruginosa outer membrane to β-lactams. The methodology we develop to determine the permeability can be applied to other antibiotic families and/or pathogens.

Understanding resistance acquisition by Pseudomonas aeruginosa and possible pharmacological approaches in palliating its pathogenesis

Pseudomonas aeruginosa can utilize various virulence factors necessary for host infection and persistence. These virulence factors include pyocyanin, proteases, exotoxins, 2-heptyl-4-hydroxyquinoline N-oxide (HQNO), phospholipases, and siderophores that enable the bacteria to cause severe infections in immunocompromised individuals. P. aeruginosa falls into the category of nosocomial pathogens that are typically resistant to available antibiotics and therapeutic approaches. P. aeruginosa bio-film formation is a major concern in hospitals because it can cause chronic infection and increase the risk of mortality. Therefore, the development of new strategies to disrupt biofilm formation and improve antibiotic efficacy for the treatment of P. aeruginosa infections is crucial. Anti-biofilm and anti-quorum sensing (QS) activity can be viewed as an anti-virulence approach to control the infectious nature of P. aeruginosa. Inhibition of QS and biofilm formation can be achieved through pharmacological approaches such as phytochemicals and essential oils, which have shown promising results in laboratory studies. A regulatory protein called LasR plays a key role in QS signaling to coordinate gene expression. Designing an antagonist molecule that mimics the natural autoinducer might be the best approach for LasR inhibition. Here we reviewed the mechanism behind antibiotic resistance and alternative approaches to combat the pathogenicity of P. aeruginosa.

Revealing the single-channel characteristics of OprD (OccAB1) porins from hospital strains of Acinetobacter baumannii

Nowadays, reports of antimicrobial resistance (AMR) against many antibiotics are increasing because of their misapplication. With this rise, there is a serious decrease in the discovery and development of new types of antibiotics amid an increase in multi-drug resistance. Unfermented Acinetobacter baumannii from gram-negative bacteria, which is one of the main causes of nosocomial infections and multi-drug resistance, has 4 main kinds of antibiotic resistance mechanism: inactivating antibiotics by enzymes, reduced numbers of porins and changing of their target or cellular functions due to mutations, and efflux pumps. In this study, characterization of the possible mutations in OprD (OccAB1) porins from hospital strains of A. baumannii were investigated using single channel electrophysiology and compared with the standard OprD isolated from wild type ATCC 19,606. For this aim, 5 A. baumannii bacteria samples were obtained from patients infected with A. baumannii, after which OprD porins were isolated from these A. baumannii strains. OprD porins were then inserted in an artificial lipid bilayer and the current-voltage curves were obtained using electrical recordings through a pair of Ag/AgCl electrodes. We observed that each porin has a characteristic conductance and single channel recording, which then leads to differences in channel diameter. Finally, the single channel data have been compared with the gene sequences of each porin. It was interesting to find out that each porin isolated has a unique porin diameter and decreased anion selectivity compared to the wild type.

Outer membrane permeability: Antimicrobials and diverse nutrients bypass porins in Pseudomonas aeruginosa

Novel antibiotics are urgently needed to resolve the current antimicrobial resistance crisis. For critical pathogens, drug entry through the cell envelope is one of the major challenges in the development of effective novel antibiotics. Envelope proteins forming water-filled channels, so-called porins, are commonly thought to be essential for entry of hydrophilic molecules, but we show here for the critical pathogen Pseudomonas aeruginosa that almost all antibiotics and diverse hydrophilic nutrients bypass porins and instead permeate directly through the outer membrane lipid bilayer. However, carboxylate groups hinder bilayer penetration, and Pseudomonas thus needs porins for efficient utilization of carboxylate-containing nutrients such as succinate. The major porin-independent entry route might open opportunities for facilitating drug delivery into bacteria.

Gram-negative bacterial pathogens have an outer membrane that restricts entry of molecules into the cell. Water-filled protein channels in the outer membrane, so-called porins, facilitate nutrient uptake and are thought to enable antibiotic entry. Here, we determined the role of porins in a major pathogen, Pseudomonas aeruginosa, by constructing a strain lacking all 40 identifiable porins and 15 strains carrying only a single unique type of porin and characterizing these strains with NMR metabolomics and antimicrobial susceptibility assays. In contrast to common assumptions, all porins were dispensable for Pseudomonas growth in rich medium and consumption of diverse hydrophilic nutrients. However, preferred nutrients with two or more carboxylate groups such as succinate and citrate permeated poorly in the absence of porins. Porins provided efficient translocation pathways for these nutrients with broad and overlapping substrate selectivity while efficiently excluding all tested antibiotics except carbapenems, which partially entered through OprD. Porin-independent permeation of antibiotics through the outer-membrane lipid bilayer was hampered by carboxylate groups, consistent with our nutrient data. Together, these results challenge common assumptions about the role of porins by demonstrating porin-independent permeation of the outer-membrane lipid bilayer as a major pathway for nutrient and drug entry into the bacterial cell.