Treatment ofPseudomonas aeruginosainfection in critically ill patients

Prevalence and Trends of Carbapenem-Resistant Pseudomonas aeruginosa and Acinetobacter Species Isolated from Clinical Specimens at the Ethiopian Public Health Institute, Addis Ababa, Ethiopia: A Retrospective Analysis

Purpose

Carbapenem-resistant Acinetobacter species and P. aeruginosa are the leading cause of nosocomial infections. Therefore, the objective of this study was to analyze the prevalence, antimicrobial susceptibility profile, and trends of carbapenem-resistant P. aeruginosa and Acinetobacter species isolated from clinical specimens.

Patients and Methods

This retrospective study included data from Ethiopian Public Health Institute from 2017 to 2021. BD phoenix M50, Vitek 2 compact, and conventional identification methods were used to identify the organisms. The Kirby-Bauer disc diffusion, BD phoenix M50, and Vitek 2 compact methods were used to determine the antimicrobial susceptibility profiles of the isolates. Chi-square for linear trends using Epi Info was employed to test the significance of carbapenem resistance trends over time. The p-values of ≤0.05 were considered statistically significant.

Results

Following data cleaning, 7110 reports were used. Out of this, (N=185, 2.6%) and (N=142, 2%), Acinetobacter species and P. aeruginosa were isolated, respectively. Twenty-four Acinetobacter species and fourteen P. aeruginosa species were omitted because carbapenem antimicrobial agents were not tested for them. The overall prevalence of carbapenem-resistant Acinetobacter species and P. aeruginosa were 61% and 22%, respectively. The prevalence of carbapenem-resistant Acinetobacter species increased significantly from 50% in 2017 to 76.2% in 2021 (p=0.013). The trend of carbapenem-resistant P. aeruginosa was fluctuating (p=0.99). Carbapenem-resistant Acinetobacter had a lower resistance rate to amikacin (44%) and tobramycin (55%); similarly, carbapenem-resistant P. aeruginosa had a lower resistance rate to amikacin (27%) and tobramycin (47%).

Conclusion

This study revealed a high prevalence of carbapenem-resistant Acinetobacter species and P. aeruginosa, both of which showed better sensitivity to amikacin and tobramycin. Furthermore, Acinetobacter species showed a statistically significant increasing trend in carbapenem resistance.

Discovery of an inhibitor of the production of the Pseudomonas aeruginosa virulence factor pyocyanin in wild-type cells

Pyocyanin is a small molecule produced by Pseudomonas aeruginosa that plays a crucial role in the pathogenesis of infections by this notorious opportunistic pathogen. The inhibition of pyocyanin production has been identified as an attractive antivirulence strategy for the treatment of P. aeruginosa infections. Herein, we report the discovery of an inhibitor of pyocyanin production in cultures of wild-type P. aeruginosa which is based around a 4-alkylquinolin-2(1H)-one scaffold. To the best of our knowledge, this is the first reported example of pyocyanin inhibition by a compound based around this molecular framework. The compound may therefore be representative of a new structural sub-class of pyocyanin inhibitors, which could potentially be exploited in in a therapeutic context for the development of critically needed new antipseudomonal agents. In this context, the use of wild-type cells in this study is notable, since the data obtained are of direct relevance to native situations. The compound could also be of value in better elucidating the role of pyocyanin in P. aeruginosa infections. Evidence suggests that the active compound reduces the level of pyocyanin production by inhibiting the cell–cell signalling mechanism known as quorum sensing. This could have interesting implications; quorum sensing regulates a range of additional elements associated with the pathogenicity of P. aeruginosa and there is a wide range of other potential applications where the inhibition of quorum sensing is desirable.

Surveillance and management of multidrug-resistant microorganisms

Multidrug-resistant organisms are an established and growing worldwide public health problem and few therapeutic options remain available. The traditional antimicrobials (glycopeptides) for multidrug-resistant Gram-positive infections are declining in efficacy. New drugs that are presently available are linezolid, daptomicin and tigecycline, which have well-defined indications for severe infections, and talavancin, which is under Phase III trial for hospital-acquired pneumonia. Unfortunately the therapies available for multidrug-resistant Gram-negatives, including carbapenem-resistant Pseudomonas aeruginosa, Acinetobacter baumannii and Enterobacteriaceae, are limited to only colistin and tigecycline. Both of these drugs are still not registered for severe infections, such as hospital acquired pneumonia. Consequently, as confirmed by scientific evidence, a multidisciplinary approach is needed. Surveillance, infection control procedures, isolation and antimicrobial stewardship should be implemented to reduce multidrug-resistant organism diffusion.

Applications of small molecule activators and inhibitors of quorum sensing in Gram-negative bacteria

Quorum sensing is a form of intercellular communication used by many species of bacteria that facilitates concerted interactions between the cells comprising a population. The phenotypes regulated by quorum sensing are extremely diverse, with many having a significant impact upon healthcare, agriculture, and the environment. Consequently there has been significant interest in developing methods to manipulate this signalling process and recent years have witnessed significant theoretical and practical developments. A wide range of small molecule modulators of quorum sensing systems has been discovered, providing an expansive chemical toolbox for the study and modulation of this signalling mechanism. In this review, a selection of recent case studies which illustrate the value of both activators and inhibitors of quorum sensing in Gram-negative bacteria are discussed.

Design, synthesis and biological evaluation of non-natural modulators of quorum sensing in Pseudomonas aeruginosa

Many species of bacteria employ a mechanism of intercellular communication known as quorum sensing which is mediated by small diffusible signalling molecules termed autoinducers. The most common class of autoinducer used by Gram-negative bacteria are N-acylated-L-homoserine lactones (AHLs). Pseudomonas aeruginosa is a clinically important bacterium which is known to use AHL-mediated quorum sensing systems to regulate a variety of processes associated with virulence. Thus the selective disruption of AHL-based quorum sensing represents a strategy to attenuate the pathogenicity of this bacterium. Herein we describe the design, synthesis and biological evaluation of a collection of structurally novel AHL mimics. A number of new compounds capable of modulating the LasR-dependent quorum sensing system of P. aeruginosa were identified, which could have value as molecular tools to study and manipulate this signalling pathway. Worthy of particular note, this research has delivered novel potent quorum sensing antagonists, which strongly inhibit the production of virulence factors in a wild type strain of this pathogenic bacterium.

Fatal hemorrhage in two renal graft recipients with multi-drug resistant Pseudomonas aeruginosa infection

Pseudomonas aeruginosa (PA) infections occurring after renal transplantation (RT) represent a potentially life-threatening complication. We present 2 cases of early death following RT in which PA was transmitted, possibly from the donor to the recipients, despite preoperative cultures that were negative. The donor had developed PA-related bilateral pneumonia while in the intensive care unit. However, after appropriate antibiotic therapy, no signs of infection were present at the time of organ retrieval and cultures were negative. Both recipients received a renal graft from the same donor and developed multi-drug resistant (MDR)-PA infections with bacterial phenotypes and resistances similar to the donor. The first recipient died 9 days after RT from rupture of a false aneurysm of the external iliac artery, caused by a fully thickened PA-related arteritis. The second recipient died postoperatively on day 10 after rupture of an aneurysm in the right vertebral artery. Our experience shows that MDR-PA infection early after RT may be a catastrophic event. Specific anti-PA antibiotic therapy in RT patients during the perioperative period is recommended in the case of PA infection in the donor, even after apparent successful therapy with negative cultures.

Development and qualification of a pharmacodynamic model for the pronounced inoculum effect of ceftazidime against Pseudomonas aeruginosa

Evidence is mounting in support of the inoculum effect (i.e., slow killing at large initial inocula [CFUo]) for numerous antimicrobials against a variety of pathogens. Our objectives were to (i) determine the impact of the CFUo of Pseudomonas aeruginosa on ceftazidime activity and (ii) to develop and validate a pharmacokinetic/pharmacodynamic (PKPD) mathematical model accommodating a range of CFUo. Time-kill experiments using ceftazidime at seven concentrations up to 128 mg/liter (MIC, 2 mg/liter) were performed in duplicate against P. aeruginosa PAO1 at five CFUo from 10(5) to 10(9) CFU/ml. Samples were collected over 24 h and fit by candidate models in NONMEM VI and S-ADAPT 1.55 (all data were comodeled). External model qualification integrated data from eight previously published studies. Ceftazidime displayed approximately 3 to 4 log(10) CFU/ml net killing at 10(6.2) CFUo and concentrations of 4 mg/liter (or higher), less than 1.6 log(10) CFU/ml killing at 10(7.3) CFUo, and no killing at 10(8.0) CFUo for concentrations up to 128 mg/liter. The proposed mechanism-based model successfully described the inoculum effect and the concentration-independent lag time of killing. The mean generation time was 28.3 min. The effect of an autolysin was assumed to inhibit successful replication. Ceftazidime concentrations of 0.294 mg/liter stimulated the autolysin effect by 50%. The model was predictive in the internal cross-validation and had excellent in silico predictive performance for published studies of P. aeruginosa ATCC 27853 for various CFUo. The proposed PKPD model successfully described and predicted the pronounced inoculum effect of ceftazidime in vitro and integrated data from eight literature studies to support translation from time-kill experiments to in vitro infection models.