Ultra-rapid flow cytometry assay for colistin MIC determination in Enterobacterales, Pseudomonas aeruginosa and Acinetobacter baumannii

Flow Cytometry as a Rapid and Valuable Method in Investigation of Colistin Resistance in Carbapenem-Resistant Klebsiella pneumoniae Isolates

Rapid detection of antimicrobial resistance is crucial for early initiation of appropriate therapy. The aim of this study was to investigate whether resistance to colistin, the last-resort antibiotic, in carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates can be detected accurately and rapidly by flow cytometry (FCM). The VITEK 2 automated system was used to identify 85 K. pneumoniae strains and to determine their resistance to carbapenems. The minimum inhibitory concentration (MIC) values for colistin in 85 CRKP strains were determined by broth microdilution (BMD), which is the reference method. In addition, FCM was used, combined with DiBAC4(3) fluorescent stain, to determine colistin susceptibility. The MIC₅₀ value of the strains, 80% of which were resistant to colistin by the BMD method, was 16 mg/L, and the MIC₉₀ value was 32 mg/L. When FCM was compared with the reference method, it was determined that the specificity was 94.1%, sensitivity was 100% of FCM, and Cohen's kappa value was 0.96. Colistin susceptibility results with FCM were obtained within an average of 2 h. These findings suggest that FCM holds great promise as a rapid and reliable alternative method for detecting colistin resistance in CRKP strains.

Antibacterial Property of Silver Nanoparticles Green Synthesized from Stachys schtschegleevii Plant Extract on Urinary Tract Infection Bacteria

Urinary tract infections are one of the most common infections worldwide. Given the increasing antibiotic resistance, monitoring antibiotic sensitivity patterns is crucial. Furthermore, silver nanoparticles synthesized from Stachys schtschegleevii can exhibit potent antibacterial, antibiotic, and antifungal properties. The plant S. schtschegleevii was collected from its natural habitat, dried, and its extract was then exposed to silver nitrate. Under specific conditions, silver nanoparticles were synthesized from it. Subsequently, the production and validation of silver nanoparticles were confirmed through techniques such as FTIR analysis, UV-Vis analysis, TEM, SEM, EDX analysis, and zeta potential analysis. In the in vitro section of the research, the impact of the extracted silver nanoparticles on bacteria isolated from patients' urine and standard bacterial culture (control) was assessed using the disc diffusion and MIC test methods. The results of the analyses are FTIR (high protein content; proteins and phenols serve as stabilizing agents), UV-Vis (peak of 460 nm), TEM (spherical to occasionally elliptical shapes), SEM (sizes: 26 to 72 nm), EDX (peak at 3 keV), and zeta potential (- 15.76 ± 0.05 mV). The effect of silver nanoparticles by disc diffusion method (mm) is Enterococcus faecalis = 18.31 ± 0.35, Escherichia coli = 21.51 ± 0.61, and Staphylococcus aureus = 19.02 ± 1.28, and by MIC test (μg/ml), E. faecalis = 19, E. coli = 18, and Staphylococcus aureus = 16. Antibacterial activity of the silver nanoparticles synthesized from S. schtschegleevii means that these herbal nanoparticles treat urinary tract infections caused by some of the test isolates.

Sensing of Antibiotic-Bacteria Interactions

Sensing of antibiotic-bacteria interactions is an important area of research that has gained significant attention in recent years. Antibiotic resistance is a major public health concern, and it is essential to develop new strategies for detecting and monitoring bacterial responses to antibiotics in order to maintain effective antibiotic development and antibacterial treatment. This review summarizes recent advances in sensing strategies for antibiotic-bacteria interactions, which are divided into two main parts: studies on the mechanism of action for sensitive bacteria and interrogation of the defense mechanisms for resistant ones. In conclusion, this review provides an overview of the present research landscape concerning antibiotic-bacteria interactions, emphasizing the potential for method adaptation and the integration of machine learning techniques in data analysis, which could potentially lead to a transformative impact on mechanistic studies within the field.

Detection of antimicrobial impact on gram-negative bacterial cell envelope based on single-cell imaging by scanning electron microscopy

Rapid determination of drug efficacy against bacterial pathogens is needed to detect potentially resistant bacteria and allow for more rational use of antimicrobials. As an indicator of the antimicrobial effect for rapid detection, we found changes in image brightness in antimicrobial-affected bacteria by scanning electron microscopy (SEM). The cell envelopes of unaffected bacteria were stained with phosphotungstic acid (PTA), whereas the entire cells of affected bacteria were stained. Since tungsten density increases backscattered electron intensity, brighter bacterial images indicate lethal damage. We propose a simplified method for determining antimicrobial efficacy by detecting damage that occurs immediately after drug administration using tabletop SEM. This method enabled the visualization of microscopic deformations while distinguishing bacterial-cell-envelope damage on gram-negative bacteria due to image-brightness change. Escherichia coli, Acinetobacter baumannii, Enterobacter cloacae, Klebsiella pneumoniae, and Pseudomonas aeruginosa were exposed to imipenem and colistin, which affect the cell envelope through different mechanisms. Classification of single-cell images based on brightness was quantified for approximately 500 bacteria per sample, and the bright images predominated within 5 to 60 min of antimicrobial treatment, depending on the species. Using intracellular PTA staining and characteristic deformations as indicators, it was possible to determine the efficacy of antimicrobials in causing bacterial-cell-envelope damage.

Rapid Phenotypic Antimicrobial Susceptibility Testing Using a Coulter Counter and Proliferation Rate Discrepancy

The rapid determination of antimicrobial susceptibility and evidence-based antimicrobial prescription is necessary to combat widespread antimicrobial resistance and promote effectively treatment for bacterial infections. This study developed a rapid phenotypic antimicrobial susceptibility determination method competent for seamless clinical implementation. A laboratory-friendly Coulter counter-based antimicrobial susceptibility testing (CAST) was developed and integrated with bacterial incubation, population growth monitoring, and result analysis to quantitatively detect differences in bacterial growth between resistant and susceptible strains following a 2 h exposure to antimicrobial agents. The distinct proliferation rates of the different strains enabled the rapid determination of their antimicrobial susceptibility phenotypes. We evaluated the performance efficacy of CAST for 74 clinically isolated Enterobacteriaceae subjected to 15 antimicrobials. The results were consistent with those obtained via the 24 h broth microdilution method, showing 90.18% absolute categorical agreement.

Determination of antibiotic susceptibility of bacteria by flow cytometric method

In this study, it was aimed to determine the antibiotic susceptibility of bacterial strains by using flow cytometry method by comparing them with current standardized methods. Eleven clinical isolates and 6 standard bacterial strains were included in the study. MIC values were determined by broth microdilution method (BMD), VITEK 2® automated system and flow cytometric method (FCM). FCM was performed with the Accuri C6 flow cytometer. For all strains except P. aeuruginosa ATCC 27853 [BMD-FCM:r = 0.557(p = 0.048); VITEK 2-FCM:r = 0.529(p = 0.063)], E. faecalis ATCC 29212 [BMD-FCM:r = 0.393(p = 0.295); BMD-VITEK 2:r = 0.393(p = 0.295)], and vancomycin-resistant E. faecium clinical isolate [BMD-FCM:r = 0.452(p = 0.063)] r values were in the range of 0.802-0.969 for BMD-FCM (p < 0.001), 0.655-0.941 for BMD-VITEK 2 (p < 0.005) and 0.667-0.953 for FCM-VITEK 2 (p < 0.005). Correlation values of antibiotic susceptibility test results between three methods for Gram-negative bacteria were found as follows; r = 0.927(p < 0.001) for BMD-FCM, r = 0.851(p < 0.001) for BMD-VITEK 2, r = 0.807(p < 0.001) for VITEK 2-FCM. Correlation values were found as follows for Gram positive bacteria; r = 0.848(p < 0.001) for BMD-FCM, r = 0.877(p < 0.001) for BMD-VITEK 2, r = 0.800(p < 0.001) for VITEK 2-FCM. When all bacteria included in the study were evaluated as a total; it was r = 0.911(p < 0.001) for BMD-FCM, r = 0.888(p < 0.001) for BMD-VITEK 2, r = 0.835(p < 0.001) for VITEK 2-FCM. The methicillin resistance of the clinical methicillin resistant S. aureus isolate could not be detected by FCM. It was determined that there was a high level of correlation between methods. FCM shortens the duration of antibiotic susceptibility tests by 12-14 h and gives results within the same day. However, it has not been standardized to be widely used in microbiology laboratories and experienced personnel are needed for its implementation.

Diagnosis of Bloodstream Infections: An Evolution of Technologies towards Accurate and Rapid Identification and Antibiotic Susceptibility Testing

Bloodstream infections (BSI) are a leading cause of death worldwide. The lack of timely and reliable diagnostic practices is an ongoing issue for managing BSI. The current gold standard blood culture practice for pathogen identification and antibiotic susceptibility testing is time-consuming. Delayed diagnosis warrants the use of empirical antibiotics, which could lead to poor patient outcomes, and risks the development of antibiotic resistance. Hence, novel techniques that could offer accurate and timely diagnosis and susceptibility testing are urgently needed. This review focuses on BSI and highlights both the progress and shortcomings of its current diagnosis. We surveyed clinical workflows that employ recently approved technologies and showed that, while offering improved sensitivity and selectivity, these techniques are still unable to deliver a timely result. We then discuss a number of emerging technologies that have the potential to shorten the overall turnaround time of BSI diagnosis through direct testing from whole blood—while maintaining, if not improving—the current assay’s sensitivity and pathogen coverage. We concluded by providing our assessment of potential future directions for accelerating BSI pathogen identification and the antibiotic susceptibility test. While engineering solutions have enabled faster assay turnaround, further progress is still needed to supplant blood culture practice and guide appropriate antibiotic administration for BSI patients.

MICy: a Novel Flow Cytometric Method for Rapid Determination of Minimal Inhibitory Concentration

Early initiated adequate antibiotic treatment is essential in intensive care. Shortening the length of antibiotic susceptibility testing (AST) can accelerate clinical decision-making. Our objective was to develop a simple flow cytometry (FC)-based AST that produces reliable results within a few hours. We developed a FC-based AST protocol (MICy) and tested it on six different bacteria strains (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pyogenes, Enterococcus faecalis) in Mueller-Hinton and Luria-Bertani broth. We monitored the bacterial growth by FC to define the optimal time of AST. All bacteria were tested against 12 antibiotics and the MIC values were compared to microdilution used as reference method. McNemar and Fleiss' kappa inter-observer tests were performed to analyze the bias between the two methods. Susceptibility profiles of the two methods were also compared. We found that FC is able to detect the bacterial growth after 4-h incubation. The point-by-point comparison of MICy and microdilution resulted in exact match above 87% (2642/3024) of all measurements. The MIC values obtained by MICy and microdilution agreed over 80% (173/216) within ±1 dilution range that gives a substantial inter-observer agreement with weighted Fleiss' kappa. By using the EUCAST clinical breakpoints, we defined susceptibility profiles of MICy that were identical to microdilution in more than 92% (197/213) of the decisions. MICy resulted 8.7% major and 3.2% very major discrepancies. MICy is a new, simple FC-based AST method that produces susceptibility profile with low failure rate a workday earlier than the microdilution method. IMPORTANCE MICy is a new, simple and rapid flow cytometry based antibiotic susceptibility testing (AST) method that produces susceptibility profile a workday earlier than the microdilution method or other classical phenotypic AST methods. Shortening the length of AST can accelerate clinical decision-making as targeted antibiotic treatment improves clinical outcomes and reduces mortality, duration of artificial ventilation, and length of stay in intensive care unit. It can also reduce nursing time and costs and the spreading of antibiotic resistance. In this study, we present the workflow and methodology of MICy and compare the results produced by MICy to microdilution step by step.

Rapid high-resolution detection of colistin resistance in Gram-negative bacteria using flow cytometry: a comparison with broth microdilution, a commercial screening test and WGS

BACKGROUND

Even though both EUCAST and CLSI consider broth microdilution (BMD) as the reference method for antimicrobial susceptibility testing (AST) of colistin, the method exhibits potential flaws related to properties of the colistin molecule.

OBJECTIVES

To develop a flow cytometry method (FCM) for colistin AST and to validate it against BMD, a commercial screening test and WGS.

METHODS

Colistin-mediated loss of membrane integrity in Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter spp. was detected with the fluorescent probe YoPro-1 by FCM. An international collection of 65 resistant and 109 susceptible isolates were analysed and the colistin concentration required to reach the EC50 was compared with the BMD MIC and the presence of genotypic resistance markers.

RESULTS

The overall FCM sensitivity and specificity for colistin resistance was 89% and 94%, with E. coli > K. pneumoniae > P. aeruginosa, whereas the performance for Acinetobacter spp. was poor. All tested E. coli were correctly categorized. Three K. pneumoniae isolates with genotypic findings consistent with colistin resistance were detected by FCM but not BMD. Compared with BMD, FCM delivered AST results with a 75% reduction of time.

CONCLUSIONS

Here, we present a rapid FCM-based AST assay for qualitative and quantitative testing of colistin resistance in E. coli and K. pneumoniae. The assay revealed probable chromosomal colistin resistance in K. pneumoniae that was not detected by BMD. If confirmed, these results question the reliability of BMD for colistin testing.

How to: screening for mcr-mediated resistance to colistin

BACKGROUND

Colistin belongs to the last-resort antibiotics. The discovery of plasmid-bound colistin resistance mediated by the mcr-gene(s) is of great concern because, given its biological potential, there is a risk of its rapid spread.

OBJECTIVES

To discuss the current literature on the methods for the screening for mcr-mediated resistance to colistin.

SOURCES

Literature was drawn from a search of PubMed from 1 January 2016 to 26 April 2021.

CONTENT

The selective culture-based or culture-independent approach can be used for the screening of mcr-mediated resistance to colistin in clinical samples. Rapid Polymyxin NP, Colistin Drop or Colistin Agar Spot tests are applicable for the selection of isolates with a suspected resistance to colistin that has to be confirmed by broth microdilution. The mcr-mediated resistance to colistin can be confirmed by the detection of the causal gene(s) or by phenotype using EDTA-colistin broth disc elution; production of the MCR-1 enzyme can be confirmed with lateral flow immunoassay, using matrix-assisted laser desorption/ionization time-of flight or liquid chromatography-based mass spectrometry. Whole-genome sequencing (WGS) is the ultimate typing method. When a WGS platform is not available at a healthcare facility, a WGS-outsourced service, in combination with freely available bioinformatics tools, allows for the characterization of the mcr-gene(s) carrying isolates.

IMPLICATIONS

mcr-mediated colistin resistance should be monitored through active targeted screening. The broth microdilution method is required for colistin susceptibility testing but as only a selected number of clinical isolates are tested, colistin resistance, including mcr-mediated, may remain undetected. In mcr-1-positive Escherichia coli isolates, the MIC to colistin can range from 2 to 8 mg/L, so it is proposed that Enterobacterales with a colistin MIC of 2 mg/L should also be included in the mcr-mediated colistin resistance screening and those with a confirmed mcr-genotype and/or MCR-phenotype should be considered to be colistin-resistant.