Comparative evaluation of the UMIC Colistine kit to assess MIC of colistin of gram-negative rods

Crafting Stable Antibiotic Nanoparticles via Complex Coacervation of Colistin with Block Copolymers

To combat the ever-growing increase of multidrug-resistant (MDR) bacteria, action must be taken in the development of antibiotic formulations. Colistin, an effective antibiotic, was found to be nephrotoxic and neurotoxic, consequently leading to a ban on its use in the 1980s. A decade later, colistin use was revived and nowadays used as a last-resort treatment against Gram-negative bacterial infections, although highly regulated. If cytotoxicity issues can be resolved, colistin could be an effective option to combat MDR bacteria. Herein, we investigate the complexation of colistin with poly(ethylene oxide)-b-poly(methacrylic acid) (PEO-b-PMAA) block copolymers to form complex coacervate core micelles (C3Ms) to ultimately improve colistin use in therapeutics while maintaining its effectiveness. We show that well-defined and stable micelles can be formed in which the cationic colistin and anionic PMAA form the core while PEO forms a protecting shell. The resulting C3Ms are in a kinetically arrested and stable state, yet they can be made reproducibly using an appropriate experimental protocol. By characterization through dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS), we found that the best C3M formulation, based on long-term stability and complexation efficiency, is at charge-matching conditions. This nanoparticle formulation was compared to noncomplexed colistin on its antimicrobial properties, enzymatic degradation, serum protein binding, and cytotoxicity. The studies indicate that the antimicrobial properties and cytotoxicity of the colistin-C3Ms were maintained while protein binding was limited, and enzymatic degradation decreased after complexation. Since colistin-C3Ms were found to have an equal effectivity but with increased cargo protection, such nanoparticles are promising components for the antibiotic formulation toolbox.

Antimicrobial Susceptibility Testing for Colistin: Extended Application of Novel Quantitative and Morphologic Assay Using Scanning Electron Microscopy

Background

Colistin (Polymyxin E) has reemerged in the treatment of MDR Gram-negative infections. Traditional Colistin AST methods have long turnaround times and are cumbersome for routine use. We present a SEM-AST technique enabling rapid detection of Colistin resistance through direct observation of morphological and quantitative changes in bacteria exposed to Colistin.

Methods

Forty-four Gram-negative reference organisms were chosen based on their Colistin susceptibility profiles. Bacterial suspensions of ∼107 CFU/mL were exposed to Colistin at EUCAST-ECOFF, with controls not exposed, incubated at 37°C, and then sampled at 0, 15, 30, 60, and 120 minutes. Phosphotungstic Acid (PTA) staining was applied, followed by SEM imaging using Hitachi TM4000PlusII-Tabletop-SEM at ×2000, ×5000 and ×7000 magnifications. Bacterial viability analysis was performed for all conditions by quantifying viable and dead organisms based on PTA-staining and morphologic changes.

Results

We identified a significant drop in the percentage of viable organisms starting 30 minutes after exposure in susceptible strains, as compared to nonsignificant changes in resistant strains across all tested organisms. The killing effect of Colistin was best observed after 120 minutes of incubation with the antibiotic, with significant changes in morphologic features, including bacterial inflation, fusion, and lysis, observed as early as 30 minutes. Our observation matched the results of the gold standard-based broth microdilution method.

Conclusions

We provide an extended application of the proof of concept for the utilization of the SEM-AST assay for Colistin for a number of clinically relevant bacterial species, providing a rapid and reliable susceptibility profile for a critical antibiotic.

A Review of Resistance to Polymyxins and Evolving Mobile Colistin Resistance Gene (mcr) among Pathogens of Clinical Significance

The global rise in antibiotic resistance in bacteria poses a major challenge in treating infectious diseases. Polymyxins (e.g., polymyxin B and colistin) are last-resort antibiotics against resistant Gram-negative bacteria, but the effectiveness of polymyxins is decreasing due to widespread resistance among clinical isolates. The aim of this literature review was to decipher the evolving mechanisms of resistance to polymyxins among pathogens of clinical significance. We deciphered the molecular determinants of polymyxin resistance, including distinct intrinsic molecular pathways of resistance as well as evolutionary characteristics of mobile colistin resistance. Among clinical isolates, Acinetobacter stains represent a diversified evolution of resistance, with distinct molecular mechanisms of intrinsic resistance including naxD, lpxACD, and stkR gene deletion. On the other hand, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa are usually resistant via the PhoP-PhoQ and PmrA-PmrB pathways. Molecular evolutionary analysis of mcr genes was undertaken to show relative relatedness across the ten main lineages. Understanding the molecular determinants of resistance to polymyxins may help develop suitable and effective methods for detecting polymyxin resistance determinants and the development of novel antimicrobial molecules.

Mobile colistin resistance (mcr) genes and recent developments in colistin resistance detection

The peptide antibiotic colistin has been reserved as a last resort antibiotic treatment option for cases where other antibiotics including carbapenems have failed. Recent emergence of colistin resistance and discovery of mobile colistin resistance (mcr) genes, which encode the cell wall modifying phosphoethanolamine transferase enzyme, complicates the issue. The mcr genes have been associated with conjugative plasmids and can be horizontally transferred between different bacterial species. The global spread of mcr genes has been extensively documented and this warrants surveillance of the resistance genes in the community. However, susceptibility testing of colistin is fraught with practical challenges owing to the chemical nature of the drug and multiple mechanisms of resistance. Although broth microdilution is the current gold standard for colistin susceptibility testing, the method poses technical challenges. Hence, alternative detection methods for screening colistin resistance are the need of the hour. Several methods have been studied in the recent times to address this issue. In this review, we discuss some of the recent developments in the detection of colistin resistance.

Emerging Increase in Colistin Resistance Rates in Escherichia coli and Salmonella enterica from Türkiye

Foodborne infections caused by drug-resistant Salmonella spp. are a global health concern. Moreover, commensal Escherichia coli is considered risky due to the presence of antimicrobial resistance genes. Colistin is considered a last-resort antibiotic against Gram-negative bacterial infections. Colistin resistance can be transferred both vertically, and horizontally via conjugation between bacterial species. Plasmid-mediated resistance has been associated with mcr-1 to mcr-10 genes. In this study, we collected food samples (n = 238), and isolated E. coli (n = 36) and Salmonella (n = 16), representing recent isolates. We included previously collected Salmonella (n = 197) and E. coli (n = 56) from various sources from 2010 to 2015 in Türkiye as representing historical isolates to investigate colistin-resistance over time. In all isolates, colistin resistance was screened phenotypically by minimum inhibitory concentration (MIC), and then in resistant isolates, mcr-1 to mcr-5 genes were further screened. In addition, the antibiotic resistance of recent isolates was determined, and antibiotic resistance genes were investigated. We found that in total 20 Salmonella isolates (9.38%) and 23 of the E. coli isolates (25%) showed phenotypic colistin resistance. Interestingly, the majority of colistin-resistant isolates (N:32) had resistance levels above 128 mg/L. Furthermore 75% of commensal E. coli isolates recently isolated were resistant at least 3 antibiotics. Overall, we found that the colistin resistance has been increased from 8.12 to 25% in Salmonella isolates, and 7.14% to 52.8% in E. coli isolates over time. However, none of these resistant isolates carried mcr genes, most likely indicating emerging chromosomal colistin resistance.

Evaluation of Agar Dilution Method in Susceptibility Testing of Polymyxins for Enterobacteriaceae and Non-Fermentative Rods: Advantages Compared to Broth Microdilution and Broth Macrodilution

An accurate and reliable susceptibility testing method for polymyxins is urgently needed not only for the clinical laboratory but also for new polymyxin-like lipopeptide development. Reference broth microdilution (rBMD), which was the recommended method by CLSI-EUCAST in clinics, has been proven not to be ideal, while the agar dilution (AD) method that was widely used in new antibiotics discovery has been neglected. In the present study, the AD method was compared with rBMD and broth macrodilution (BMAD) in susceptibility testing of polymyxin B and colistin against >200 Gram-negative isolates. AD showed strong agreement with BMAD for colistin (except for Klebsiella aerogenes and Pseudomonas aeruginosa); however, its performance was poor for polymyxin B or compared to rBMD. MICs of AD method were not affected when different types of Petri dishes were used, while glass-bottom microtiter plates could lower the MIC of polymyxins 2−8 times compared to tissue-culture-treated polystyrene plates when using rBMD, which demonstrated that tissue-culture-treated plates were not suitable. It was then validated with non-tissue-culture-treated plates. The culture volume was another influencing factor of accuracy for rBMD, and 200 μL seemed to be the most suitable volume for MIC detection of polymyxins. Additionally, no lack of growth phenomenon (skipped well) was observed for AD when it frequently occurred for both BMAD and rBMD. As for strains carrying mcr-1 gene, 100% of AD results were in essential agreement (EA) and categorical agreement (CA) with both rBMD and BMAD. Overall, rBMD is convenient and widely accepted for susceptibility testing of polymyxins. Although it may be too early to say that AD is superior compared to rBMD and BMAD, it did show some advantages in repeatability and anti-interference ability.

Evaluation of Colistin Broth Disk Elution and Colistin Agar Test: A study from Tertiary Care Hospital, South India

Enterobacterales particularly which are resistant to carbapenem group of antibiotics (CRE) are precariously being reported worldwide. Last option for treating the infections caused by CRE are polymyxin E (Colistin) and polymyxin B. Resistance to polymyxins is on higher side because of its increased usage both clinically and non-clinically. In vitro evaluation tests for susceptibility of colistin is associated with lot of complexities due to its innate cationic properties. Hence it is essential for all diagnostic laboratory to standardize colistin testing method, so the present study was undertaken to evaluate the results of colistin broth disk elution (CBDE) and colistin agar test (CAT) in comparison with the reference broth microdilution (rBMD). About 100 CRE clinical isolates were tested, results of CBDE & CAT was compared with rBMD. Categorical agreement (CA) of CBDE was 98% with 2% of very major error (VME), CA of CAT was 99% with 1% of VME in comparison with rBMD. Because of increasing colistin resistance it is crucial to report colistin MIC with a validated method, so we would like to recommend CAT test for routine MIC reporting of colistin since it is feasible test.

Lacticaseicin 30 and Colistin as a Promising Antibiotic Formulation against Gram-Negative β-Lactamase-Producing Strains and Colistin-Resistant Strains

Antimicrobial resistance is a global health concern across the world and it is foreseen to swell if no actions are taken now. To help curbing this well announced crisis different strategies are announced, and these include the use of antimicrobial peptides (AMP), which are remarkable molecules known for their killing activities towards pathogenic bacteria. Bacteriocins are ribosomally synthesized AMP produced by almost all prokaryotic lineages. Bacteriocins, unlike antibiotics, offer a set of advantages in terms of cytotoxicity towards eukaryotic cells, their mode of action, cross-resistance and impact of microbiota content. Most known bacteriocins are produced by Gram-positive bacteria, and specifically by lactic acid bacteria (LAB). LAB-bacteriocins were steadily reported and characterized for their activity against genetically related Gram-positive bacteria, and seldom against Gram-negative bacteria. The aim of this study is to show that lacticaseicin 30, which is one of the bacteriocins produced by Lacticaseibacillus paracasei CNCM I-5369, is active against Gram-negative clinical strains (Salmonella enterica Enteritidis H10, S. enterica Typhimurium H97, Enterobacter cloacae H51, Escherichia coli H45, E. coli H51, E. coli H66, Klebsiella oxytoca H40, K. pneumoniae H71, K. variicola H77, K. pneumoniae H79, K. pneumoniae H79), whereas antibiotics failed. In addition, lacticaseicin 30 and colistin enabled synergistic interactions towards the aforementioned target Gram-negative clinical strains. Further, the combinations of lacticaseicin 30 and colistin prompted a drastic downregulation of mcr-1 and mcr-9 genes, which are associated with the colistin resistance phenotypes of these clinical strains. This report shows that lacticaseicin 30 is active against Gram-negative clinical strains carrying a rainbow of mcr genes, and the combination of these antimicrobials constitutes a promising therapeutic option that needs to be further exploited.

Draft Genome Sequence of an NDM-1-Producing Sequence Type 101 (ST101) Klebsiella pneumoniae Strain, Marseille-Q1949

A pan-drug-resistant Klebsiella pneumoniae strain was isolated from the blood of a 70-year-old critically ill patient in April 2019. Interestingly, the patient recovered and was discharged home a month later. The genome of strain Marseille-Q1949 is 5,607,584 bp long and has a 57.1% G+C content and 5,467 protein-coding genes.

Current and emerging polymyxin resistance diagnostics: A systematic review of established and novel detection methods

The emergence of polymyxin resistance, due to transferable mcr genes, threatens public and animal health as there are limited therapeutic options. As polymyxin is one of the last-line antibiotics, there is a need to contain the spread of its resistance to conserve its efficacy. Herein, we describe current and emerging polymyxin resistance diagnostics to inform faster clinical diagnostic choices. A literature search in diverse databases for studies published between 2016 and 2020 was performed. English articles evaluating colistin resistance methods/diagnostics were included. Screening resulted in the inclusion of 93 journal articles. Current colistin resistance diagnostics are either phenotypic or molecular. Broth microdilution is currently the only gold standard for determining colistin MICs (minimum inhibitory concentration). Phenotypic methods comprise of agar-based methods such as CHROMagar™ Col-APSE, SuperPolymyxin, ChromID^® Colistin R, LBJMR and LB medium; manual MIC-determiners viz., UMIC, MICRONAUT MIC-Strip and ComASP Colistin; automated antimicrobial susceptibility testing systems such as BD Phoenix, MICRONAUT-S, MicroScan, Sensititre and Vitek 2; MCR-detectors such as lateral flow immunoassay (LFI) and chelator-based assays including EDTA- and DPA-based tests, that is, combined disk test, modified colistin broth-disk elution (CBDE), Colispot, and Colistin MAC test as well as biochemical colorimetric tests, that is, Rapid Polymyxin NP test and Rapid ResaPolymyxin NP test. Molecular methods only characterize mobile colistin resistance; they include PCR, LAMP and whole-genome sequencing. Due to the faster turnaround time (≤3 h), improved sensitivity (84%-100%) and specificity (93.3%-100%) of the Rapid ResaPolymyxin NP test and Fastinov^® , we recommend this test for initial screening of colistin-resistant isolates. This can be followed by CBDE with EDTA or the LFI as they both have 100% sensitivity and a specificity of ≥94.3% for the rapid screening of mcr genes. However, molecular assays such as LAMP and PCR may be considered in well-equipped clinical laboratories.

Colistin Resistance among Enterobacteriaceae Isolated from Clinical Samples in Gaza Strip

Bacterial infections, especially drug-resistant infections, are a major global health issue. The emergence of multidrug-resistant (MDR) strains of Enterobacteriaceae and the lack of new antibiotics have worrisome prospects for all of humanity. Colistin is considered the last-line drug for MDR Gram-negative bacteria (GNB), and it is often used for treatment of respiratory infections caused by MDR-GNB. In recent years, there has been a marked increase in the incidence of colistin-resistant infections. The main objective of this study was to investigate the presence of colistin resistance among clinical GNB isolated from Gaza Strip hospitals. Clinical Enterobacteriaceae isolates (100) were obtained from microbiology laboratories of the hospitals of different geographical locations in Gaza Strip Governorate over a period of six months. Samples were cultured, and bacterial identification was performed by standard microbiological procedures. Enterobacteriaceae isolates were tested for their antimicrobial susceptibility by the disk diffusion method and the MIC method for colistin. Varying degrees of susceptibility were observed for the isolates against the tested antimicrobials even within members of the same antimicrobial class. Amikacin was the most effective drug (74%), followed by chloramphenicol (48%), fosfomycin, and gentamicin (45%). High resistance was recorded against trimethoprim (85%) and tetracycline (83%). Only 59% of the tested isolates were interpreted as susceptible, while 41% was classified as resistant. The highest resistance to colistin was found to be among the Proteus spp. (63.2%), followed by Serratia spp. (57.1%). The lowest resistance was observed among Klebsiella isolates (31.6%). Only 39.0% of meropenem-resistant Enterobacteriaceae was susceptible to colistin, while 45.8% of imipenem-resistant Enterobacteriaceae was susceptible to colistin. The overall resistance to colistin was high (41%) among tested clinical isolates. Furthermore, 89% was MDR. These limit and complicate treatment options for the infections caused by Enterobacteriaceae in Gaza Strip. This calls for immediate actions to control and monitor the use of antimicrobials in general and colistin in particular.

Rescuing the Last-Line Polymyxins: Achievements and Challenges

Antibiotic resistance is a major global health challenge and, worryingly, several key Gram negative pathogens can become resistant to most currently available antibiotics. Polymyxins have been revived as a last-line therapeutic option for the treatment of infections caused by multidrug-resistant Gram negative bacteria, in particular Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacterales. Polymyxins were first discovered in the late 1940s but were abandoned soon after their approval in the late 1950s as a result of toxicities (e.g., nephrotoxicity) and the availability of "safer" antibiotics approved at that time. Therefore, knowledge on polymyxins had been scarce until recently, when enormous efforts have been made by several research teams around the world to elucidate the chemical, microbiological, pharmacokinetic/pharmacodynamic, and toxicological properties of polymyxins. One of the major achievements is the development of the first scientifically based dosage regimens for colistin that are crucial to ensure its safe and effective use in patients. Although the guideline has not been developed for polymyxin B, a large clinical trial is currently being conducted to optimize its clinical use. Importantly, several novel, safer polymyxin-like lipopeptides are developed to overcome the nephrotoxicity, poor efficacy against pulmonary infections, and narrow therapeutic windows of the currently used polymyxin B and colistin. This review discusses the latest achievements on polymyxins and highlights the major challenges ahead in optimizing their clinical use and discovering new-generation polymyxins. To save lives from the deadly infections caused by Gram negative "superbugs," every effort must be made to improve the clinical utility of the last-line polymyxins. SIGNIFICANCE STATEMENT: Antimicrobial resistance poses a significant threat to global health. The increasing prevalence of multidrug-resistant (MDR) bacterial infections has been highlighted by leading global health organizations and authorities. Polymyxins are a last-line defense against difficult-to-treat MDR Gram negative pathogens. Unfortunately, the pharmacological information on polymyxins was very limited until recently. This review provides a comprehensive overview on the major achievements and challenges in polymyxin pharmacology and clinical use and how the recent findings have been employed to improve clinical practice worldwide.

Ultra-fast and universal detection of Gram-negative bacteria in complex samples based on colistin derivatives

Gram-negative bacteria are a significant cause of infections acquired in both hospital and community settings, resulting in a high mortality rate worldwide. Currently, a Gram-negative infection is diagnosed by symptom evaluation and is treated with empiric antibiotics which target both Gram-negative and Gram-positive bacteria. A rapid and simple diagnostic method would enable immediate and targeted treatment, while dramatically reducing antibiotic overuse. Herein, we introduce a method utilizing a fluorescent derivative of colistin (COL-FL), that can directly label the Gram-negative cell wall of live bacteria and universally detect the targets within 10 min. By using the COL-FL assay, we achieved the differential labeling of various Gram-negative pathogens related to hospital-acquired infections, which could be subsequently detected via spectrofluorometry and microscopy. Further, we determined that our method can be used for complex samples, such as combinations of multiple bacterial types; bacteria in the presence of mammalian cells; and bacteria with serum components. This assay can be integrated into a simple diagnostic platform for rapid screening tests and the stratification of Gram-negative bacterial infections in the clinic.