Comparison of Agar Dilution to Broth Microdilution for Testing In Vitro Activity of Cefiderocol against Gram-Negative Bacilli

Antimicrobial and Antibiofilm Activity of Monolaurin against Methicillin-Resistant Staphylococcus aureus Isolated from Wound Infections

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major pathogens associated with life-threatening infections, showing resistance to various antibiotics. This study aimed to assess the influence of monolaurin on biofilm-forming MRSA.

Methods

The agar dilution method determined the minimum inhibitory concentration (MIC) of monolaurin against MRSA isolates and explored its impact on the resistance profile of selected antibiotics. The assessment of combined therapy involving monolaurin and antibiotics was conducted using fractional inhibitory concentration (FIC). The tissue culture plate strategy appraised monolaurin's antibiofilm activity and its inhibitory concentration (IC50), with assessment via scanning electron microscopy. Reverse transcription polymerase chain reaction (RT-PCR) discerned a monolaurin effect on the expression of the icaD gene.

Results

Monolaurin exhibited MIC values ranging from 500 to 2000 μg/mL. FIC index showed a synergistic effect of monolaurin with β-lactam antibiotics ranging from 0.0039 to 0.25 (p < 0.001). Among the 103 investigated MRSA isolates, 44 (44.7%) displayed moderate biofilm formation, while 59 (55.3%) were strong biofilm producers. Antibiofilm activity demonstrated concentration dependence, confirming monolaurin's capacity to inhibit biofilm formation and exhibited strong eradicating effects against preformed MRSA biofilms with IC50 values of 203.6 μg/mL and 379.3 μg/mL, respectively. Scanning electron microscope analysis revealed reduced cell attachments and diminished biofilm formation compared to the control. The expression levels of the icaD gene were remarkably reduced at monolaurin concentrations of 250 and 500 μg/mL.

Conclusion

Monolaurin had significant inhibitory effects on MRSA pre-existing biofilms as well as biofilm development. So, it can be employed in the treatment of severe infections, particularly those associated with biofilm formation including catheter-associated infections.

Should we, and how to, optimize cefiderocol administration during severe nosocomial pneumonia due to carbapenem-resistant Acinetobacter baumanii? A viewpoint

OBJECTIVES

Acinetobacter baumannii is classified by the centre for Disease Control and Prevention (CDC) as an "urgent threat" due to its ability to acquire and develop resistance to multiple classes of antibiotics. As a result, it is one of the most concerning pathogens in healthcare settings, with increasing incidence of infections due to carbapenem-resistant Acinetobacter baumannii (CRAB) associated with high morbidity and mortality rates. Therefore, there are ongoing efforts to find novel treatment options, one of which is cefiderocol. We aim to review available evidence on cefiderocol use for severe nosocomial pneumonia due to carbapenem-resistant Acinetobacter baumannii.

METHODS

A comprehensive review was conducted from 2017 to 2023, covering articles from databases such as Pubmed, Scopus, and Embase, along with conference proceedings from ECCMID 2023. The primary focus was on severe nosocomial pneumonia due A. baumannii and cefiderocol.

DISCUSSION

Cefiderocol, targeting periplasmic space Penicillin-Binding Proteins (PBPs) via siderophore transport pathways, exhibits promise against multi-drug resistant Gram-negative bacilli. Its effectiveness in treating CRAB pneumonia remains debated. The CREDIBLE trial reported higher mortality with cefiderocol compared to the best available treatment, while other cohort studies showed contrasting outcomes. Patient variations and pharmacokinetic factors may underlie these discrepancies. The recommended cefiderocol dosage regimen may fall short of desired pharmacokinetic targets, especially in critically ill patients and lung infections. Pulmonary factors hindering cefiderocol's entry into bacteria through iron transporters are overlooked in clinical breakpoints. Optimized dosing or combination regimens may enhance infection site exposure and outcomes.

CONCLUSIONS

Further research is needed to determine the optimal cefiderocol dosage and administration (mono vs. dual therapy, continuous vs. intermittent infusion), in severe Acinetobacter baumannii nosocomial pneumonia.

Cefiderocol for treating severe aerobic Gram-negative bacterial infections: technology evaluation to inform a novel subscription-style payment model

Background

To limit the use of antimicrobials without disincentivising the development of novel antimicrobials, there is interest in establishing innovative models that fund antimicrobials based on an evaluation of their value as opposed to the volumes used. The aim of this project was to evaluate the population-level health benefit of cefiderocol in the NHS in England, for the treatment of severe aerobic Gram-negative bacterial infections when used within its licensed indications. The results were used to inform the National Institute for Health and Care Excellence guidance in support of commercial discussions regarding contract value between the manufacturer and NHS England.

Methods

The health benefit of cefiderocol was first derived for a series of high-value clinical scenarios. These represented uses that were expected to have a significant impact on patients' mortality risks and health-related quality of life. The clinical effectiveness of cefiderocol relative to its comparators was estimated by synthesising evidence on susceptibility of the pathogens of interest to the antimicrobials in a network meta-analysis. Patient-level costs and health outcomes of cefiderocol under various usage scenarios compared with alternative management strategies were quantified using decision modelling. Results were reported as incremental net health effects expressed in quality-adjusted life-years, which were scaled to 20-year population values using infection number forecasts based on data from Public Health England. The outcomes estimated for the high-value clinical scenarios were extrapolated to other expected uses for cefiderocol.

Results

Among Enterobacterales isolates with the metallo-beta-lactamase resistance mechanism, the base-case network meta-analysis found that cefiderocol was associated with a lower susceptibility relative to colistin (odds ratio 0.32, 95% credible intervals 0.04 to 2.47), but the result was not statistically significant. The other treatments were also associated with lower susceptibility than colistin, but the results were not statistically significant. In the metallo-beta-lactamase Pseudomonas aeruginosa base-case network meta-analysis, cefiderocol was associated with a lower susceptibility relative to colistin (odds ratio 0.44, 95% credible intervals 0.03 to 3.94), but the result was not statistically significant. The other treatments were associated with no susceptibility. In the base case, patient-level benefit of cefiderocol was between 0.02 and 0.15 quality-adjusted life-years, depending on the site of infection, the pathogen and the usage scenario. There was a high degree of uncertainty surrounding the benefits of cefiderocol across all subgroups. There was substantial uncertainty in the number of infections that are suitable for treatment with cefiderocol, so population-level results are presented for a range of scenarios for the current infection numbers, the expected increases in infections over time and rates of emergence of resistance. The population-level benefits varied substantially across the base-case scenarios, from 896 to 3559 quality-adjusted life-years over 20 years.

Conclusion

This work has provided quantitative estimates of the value of cefiderocol within its areas of expected usage within the NHS.

Limitations

Given existing evidence, the estimates of the value of cefiderocol are highly uncertain.

Future work

Future evaluations of antimicrobials would benefit from improvements to NHS data linkages; research to support appropriate synthesis of susceptibility studies; and application of routine data and decision modelling to assess enablement value.

Study registration

No registration of this study was undertaken.

Funding

This award was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment Policy Research Programme (NIHR award ref: NIHR135591), conducted through the Policy Research Unit in Economic Methods of Evaluation in Health and Social Care Interventions, PR-PRU-1217-20401, and is published in full in Health Technology Assessment; Vol. 28, No. 28. See the NIHR Funding and Awards website for further award information.

Determination of minimum inhibitory concentrations using machine-learning-assisted agar dilution

Effective policy to address the global threat of antimicrobial resistance requires robust antimicrobial susceptibility data. Traditional methods for measuring minimum inhibitory concentration (MIC) are resource intensive, subject to human error, and require considerable infrastructure. AIgarMIC streamlines and standardizes MIC measurement and is especially valuable for large-scale surveillance activities. MICs were measured using agar dilution for n = 10 antibiotics against clinical Enterobacterales isolates (n = 1,086) obtained from a large tertiary hospital microbiology laboratory. Escherichia coli (n = 827, 76%) was the most common organism. Photographs of agar plates were divided into smaller images covering one inoculation site. A labeled data set of colony images was created and used to train a convolutional neural network to classify images based on whether a bacterial colony was present (first-step model). If growth was present, a second-step model determined whether colony morphology suggested antimicrobial growth inhibition. The ability of the AI to determine MIC was then compared with standard visual determination. The first-step model classified bacterial growth as present/absent with 94.3% accuracy. The second-step model classified colonies as "inhibited" or "good growth" with 88.6% accuracy. For the determination of MIC, the rate of essential agreement was 98.9% (644/651), with a bias of -7.8%, compared with manual annotation. AIgarMIC uses artificial intelligence to automate endpoint assessments for agar dilution and potentially increases throughput without bespoke equipment. AIgarMIC reduces laboratory barriers to generating high-quality MIC data that can be used for large-scale surveillance programs.

IMPORTANCE

This research uses modern artificial intelligence and machine-learning approaches to standardize and automate the interpretation of agar dilution minimum inhibitory concentration testing. Artificial intelligence is currently of significant topical interest to researchers and clinicians. In our manuscript, we demonstrate a use-case in the microbiology laboratory and present validation data for the model's performance against manual interpretation.

Novel synergistic interactions between monolaurin, a mono-acyl glycerol and β lactam antibiotics against Staphylococcus aureus: an in vitro study

BACKGROUND

A major worldwide health issue is the rising frequency of resistance of bacteria.Drug combinations are a winning strategy in fighting resistant bacteria and might help in protecting the existing drugs.Monolaurin is natural compound extracted from coconut oil and has a promising antimicrobial activity against Staphylococcus.aureus. This study aims to examine the efficacy of monolaurin both individually and in combination with β-lactam antibiotics against Staphylococcus aureus isolates.

METHODS

Agar dilution method was used for determination of minimum inhibitory concentration (MIC) of monolaurin against S.aureus isolates. Scanning electron microscope (SEM) was used to detect morphological changes in S.aureus after treatment with monolaurin. Conventional and Real-time Polymerase chain reaction (RT-PCR) were performed to detect of beta-lactamase (blaZ) gene and its expressional levels after monolaurin treatment. Combination therapy of monolaurin and antibiotics was assessed through fractional inhibitory concentration and time-kill method.

RESULTS

The antibacterial activity of monolaurin was assessed on 115 S.aureus isolates, the MIC of monolaurin were 250 to 2000 µg/ml. SEM showed cell elongation and swelling in the outer membrane of S.aureus in the prescence of 1xMIC of monolaurin. blaZ gene was found in 73.9% of S.aureus isolates. RT-PCR shows a significant decrease in of blaZ gene expression at 250 and 500 µg/ml of monolaurin. Synergistic effects were detected through FIC method and time killing curve. Combination therapy established a significant reduction on the MIC value. The collective findings from the antibiotic combinations with monolaurin indicated synergism rates ranging from 83.3% to 100%.In time-kill studies, combination of monolaurin and β-lactam antibiotics produced a synergistic effect.

CONCLUSION

This study showed that monolaurin may be a natural antibacterial agent against S. aureus, and may be an outstanding modulator of β-lactam drugs. The concurrent application of monolaurin and β-lactam antibiotics, exhibiting synergistic effects against S. aureus in vitro, holds promise as potential candidates for the development of combination therapies that target particularly, patients with bacterial infections that are nearly incurable.

In vitro activity of the newly approved antimicrobial agent Cefiderocol against Carbapenem resistant Gram negative clinical isolates

INTRODUCTION

Carbapenem resistant Gram negative bacteria have emerged as priority pathogens in recent years. Cefiderocol is a siderophore cephalosporin licensed in 2019 with claimed activity against ESBL producing and carbapenem resistant bacteria with much better safety margin compared to colistin. The present study was undertaken to assess the in vitro activity of cefiderocol against carbapenem resistant clinical isolates, compared to some select antimicrobial agents including colistin.

MATERIALS AND METHODS

Seventy-seven isolates of Gram negative bacteria belonging to the three commonly encountered groups of Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter spp were included. Susceptibility testing for Cefiderocol was determined by Kirby-Bauer's disk diffusion technique as per CLSI guidelines using Cefiderocol disc (30 μg). Sensitivity for the other agents were determined using automated system.

RESULTS

Of the 77 isolates, 58.4% belonged to Enterobacterales, followed by P.aeruginosa (27.3%) and Acinetobacter spp (14.3%). Three out of 45 Enterobacterales isolates, one out of 21 P.aeruginosa and none in the Acinetobacter group were found resistant to cefiderocol. All the isolates were intermediate sensitive (I) for colistin since the "susceptible" interpretive category has been eliminated. Tigecycline showed good activity (80.0% sensitive) against Enterobacterales followed by aztreonam (71.1% sensitive).

CONCLUSION

Cefiderocol is not yet available in India and our study is possibly the second one from this country demonstrating in vitro resistance to this important antimicrobial agent. However, with a relatively better safety profile compared to colistin, cefiderocol can be an important agent to combat these highly resistant pathogens.

Global prevalence of cefiderocol non-susceptibility in Enterobacterales, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia: a systematic review and meta-analysis

BACKGROUND

Cefiderocol is a last resort option for carbapenem-resistant (CR) Gram-negative bacteria, especially metallo-β-lactamase-producing Pseudomonas aeruginosa and CR Acinetobacter baumannii. Monitoring global levels of cefiderocol non-susceptibility (CFDC-NS) is important.

OBJECTIVES

To systematically collate and examine studies investigating in vitro CFDC-NS and estimate the global prevalence of CFDC-NS against major Gram-negative pathogens.

DATA SOURCES

PubMed and Scopus, up to May 2023.

STUDY ELIGIBILITY CRITERIA

Eligible were studies reporting CFDC-NS in Enterobacterales, P. aeruginosa, A. baumannii, or Stenotrophomonas maltophilia clinical isolates.

RISK-OF-BIAS ASSESSMENT

Two independent reviewers extracted study data and assessed the risk of bias on the population, setting, and measurement (susceptibility testing) domains.

DATA SYNTHESIS

Binomial-Normal mixed-effects models were applied to estimate CFDC-NS prevalence by species, coresistance phenotype, and breakpoint definition (EUCAST, CLSI, and FDA). Sources of heterogeneity were investigated by subgroup and meta-regression analyses.

RESULTS

In all, 78 studies reporting 82 035 clinical isolates were analysed (87% published between 2020 and 2023). CFDC-NS prevalence (EUCAST breakpoints) was low overall but varied by species (S. maltophilia 0.4% [95% CI 0.2-0.7%], Enterobacterales 3.0% [95% CI 1.5-6.0%], P. aeruginosa 1.4% [95% CI 0.5-4.0%]) and was highest for A. baumannii (8.8%, 95% CI 4.9-15.2%). CFDC-NS was much higher in CR Enterobacterales (12.4%, 95% CI 7.3-20.0%) and CR A. baumannii (13.2%, 95% CI 7.8-21.5%), but relatively low for CR P. aeruginosa (3.5%, 95% CI 1.6-7.8%). CFDC-NS was exceedingly high in New Delhi metallo-β-lactamase-producing Enterobacterales (38.8%, 95% CI 22.6-58.0%), New Delhi metallo-β-lactamase-producing A. baumannii (44.7%, 95% CI 34.5-55.4%), and ceftazidime/avibactam-resistant Enterobacterales (36.6%, 95% CI 22.7-53.1%). CFDC-NS varied considerably with breakpoint definition, predominantly among CR bacteria. Additional sources of heterogeneity were single-centre investigations and geographical regions.

CONCLUSIONS

CFDC-NS prevalence is low overall, but alarmingly high for specific CR phenotypes circulating in some institutions or regions. Continuous surveillance and updating of global CFDC-NS estimates are imperative while cefiderocol is increasingly introduced into clinical practice. The need to harmonize EUCAST and CLSI breakpoints was evident.

In vitro activity of cefiderocol, a siderophore cephalosporin, against carbapenem-resistant hypervirulent Klebsiella pneumoniae in China

Cefiderocol is a siderophore cephalosporin that binds ferric iron and utilizes iron transporters to cross the cell membrane. Hypervirulent Klebsiella pneumoniae (hvKp) is known to produce more siderophores; in this case, the uptake of cefiderocol may be decreased. Therefore, the objective of this study was to evaluate the in vitro activity of cefiderocol against hvKp isolates. A total of 320 carbapenem-resistant K. pneumoniae (CRKp) isolates were collected in China between 2014 and 2022, including 171 carbapenem-resistant hvKp (CR-hvKp) and 149 carbapenem-resistant classical K. pneumoniae (CR-cKp). Quantitative detection of siderophores showed that the average siderophore production of CR-hvKp (234.6 mg/L) was significantly higher than that of CR-cKp (68.9 mg/L, P < 0.001). The overall cefiderocol resistance rate of CR-hvKp and CR-cKp was 5.8% (10/171) and 2.7% (4/149), respectively. The non-susceptible rates of both cefiderocol and siderophore production of CR-hvKp isolates were higher than those of CR-cKp in either NDM-1- or KPC-2-producing groups. The MIC90 and MIC50 for CR-hvKp and CR-cKp were 8 mg/L and 2 mg/L and 4 mg/L and 1 mg/L, respectively. The cumulative cefiderocol MIC distribution for CR-hvKp was significantly lower than that of CR-cKp isolates (P = 0.003). KL64 and KL47 consisted of 53.9% (83/154) and 75.7% (53/70) of the ST11 CR-hvKp and CR-cKp, respectively, and the former had significantly higher siderophore production. In summary, cefiderocol might be less effective against CR-hvKp compared with CR-cKp isolates, highlighting the need for caution regarding the prevalence of cefiderocol-resistant K. pneumoniae strains, particularly in CR-hvKp isolates.

Heteroresistance to cefiderocol in carbapenem-resistant Acinetobacter baumannii in the CREDIBLE-CR study was not linked to clinical outcomes: a post hoc analysis

IMPORTANCE

The population analysis profiling (PAP) test is considered the "gold standard" method to detect heteroresistance. It exposes bacteria to increasing concentrations of antibiotics at high cell densities to detect any minority resistant subpopulations that might be missed by the low inoculums used for reference susceptibility tests. However, its clinical relevance has not been well established. In the CREDIBLE-CR study, a numerically increased all-cause mortality was observed in the cefiderocol arm relative to the best available therapy arm for patients with Acinetobacter spp. infections. Heteroresistance has independently been proposed by another research group as a potential explanation of the mortality difference. An analysis of the baseline carbapenem-resistant Acinetobacter calcoaceticus-baumannii complex isolates from patients treated with cefiderocol in the CREDIBLE-CR study showed the highest clinical cure rate and the lowest mortality for patients with PAP-heteroresistant isolates compared with PAP-susceptible or PAP-resistant isolates. These findings contradict the abovementioned hypothesis that heteroresistance contributed to the increased mortality.

Comparison of Disk Diffusion, E-Test, and Broth Microdilution Methods for Testing In Vitro Activity of Cefiderocol in Acinetobacter baumannii

The reference method for cefiderocol antimicrobial susceptibility testing is broth microdilution (BMD) with iron-depleted-Mueller-Hinton (ID-MH) medium, whereas breakpoints recommended for disk diffusion (DD) are based on MH-agar plates. We aimed to compare the performance of the commercial BMD tests ComASP (Liofilchem) and UMIC (Bruker), and DD and E-test using MH- and ID-MH-agar plates with the reference BMD method using 100 carbapenem-resistant-A. baumannii isolates. Standard BMD was performed according to the EUCAST guidelines; DD and E-test were carried out using two commercial MH-agar plates (BioMérieux and Liofilchem) and an in-house ID-MH-agar plate, while ComASP and UMIC were performed according to the manufacturer's guidelines. DD performed with the ID-MH-agar plates led to a higher categorical agreement (CA, 95.1%) with standard BMD and fewer categorization errors compared to the commercial MH-agar plates (CA BioMérieux 91.1%, Liofilchem 89.2%). E-test on ID-MH-agar plates exhibited a significantly higher essential agreement (EA, 75%) with standard BMD compared to the two MH-agar plates (EA BioMérieux 57%, Liofilchem 44%), and showed a higher performance in detecting high-level resistance than ComASP and UMIC (mean log2 difference with standard BMD for resistant isolates of 0.5, 2.83, and 2.08, respectively). In conclusion, DD and E-test on ID-MH-agar plates exhibit a higher diagnostic performance than on MH-agar plates and the commercial BMD methods. Therefore, we recommend using ID-MH-agar plates for cefiderocol susceptibility testing of A. baumannii.

Cefiderocol Treatment for Severe Infections due to Difficult-to-Treat-Resistant Non-Fermentative Gram-Negative Bacilli in ICU Patients: A Case Series and Narrative Literature Review

Cefiderocol (FDC) is a siderophore cephalosporin now recognized as a new weapon in the treatment of difficult-to-treat-resistant (DTR) Gram-negative pathogens, including carbapenemase-producing enterobacterales and non-fermentative Gram-negative bacilli (GNB). This article reports our experience with an FDC-based regimen in the treatment of 16 extremely severe patients (invasive mechanical ventilation, 15/16; extracorporeal membrane oxygenation, 9/16; and renal replacement therapy, 8/16) infected with DTR GNB. Our case series provides detailed insight into the pharmacokinetic profile and the microbiological data in real-life conditions. In the narrative review, we discuss the interest of FDC in the treatment of non-fermentative GNB in critically ill patients. We reviewed the microbiological spectrum, resistance mechanisms, pharmacokinetics/pharmacodynamics, efficacy and safety profiles, and real-world evidence for FDC. On the basis of our experience and the available literature, we discuss the optimal FDC-based regimen, FDC dosage, and duration of therapy in critically ill patients with DTR non-fermentative GNB infections.

In Vitro Activity of Cefiderocol on Multiresistant Bacterial Strains and Genomic Analysis of Two Cefiderocol Resistant Strains

Cefiderocol is a new siderophore cephalosporin that is effective against multidrug-resistant Gram-negative bacteria, including carbapenem-resistant strains. The aim of this study was to evaluate the activity of this new antimicrobial agent against a collection of pathogens using broth microdilution assays and to analyze the possible mechanism of cefiderocol resistance in two resistant Klebsiella pneumoniae isolates. One hundred and ten isolates were tested, comprising 67 Enterobacterales, two Acinetobacter baumannii, one Achromobacter xylosoxidans, 33 Pseudomonas aeruginosa and seven Stenotrophomonas maltophilia. Cefiderocol showed good in vitro activity, with an MIC < 2 μg/mL, and was able to inhibit 94% of the tested isolates. We observed a resistance rate of 6%. The resistant isolates consisted of six Klebsiella pneumoniae and one Escherichia coli, leading to a resistance rate of 10.4% among the Enterobacterales. Whole-genome sequencing analysis was performed on two cefiderocol-resistant Klebsiella pneumoniae isolates to investigate the possible mutations responsible for the observed resistance. Both strains belonged to ST383 and harbored different resistant and virulence genes. The analysis of genes involved in iron uptake and transport showed the presence of different mutations located in fhuA, fepA, iutA, cirA, sitC, apbC, fepG, fepC, fetB, yicI, yicJ, and yicL. Furthermore, for the first time, to the best of our knowledge, we described two Klebsiella pneumoniae isolates that synthesize a truncated fecA protein due to the transition from G to A, leading to a premature stop codon in the amino acid position 569, and a TonB protein carrying a 4-amino acid insertion (PKPK) after Lysine 103. In conclusion, our data show that cefiderocol is an effective drug against multidrug-resistant Gram-negative bacteria. However, the higher resistance rate observed in Enterobacterales underlines the need for active surveillance to limit the spread of these pathogens and to avoid the risks associated with the emergence of resistance to new drugs.

Evaluation of Variability in Interpretation of Disk Diffusion Testing for Cefiderocol Using Different Brands of Mueller-Hinton Agar

BACKGROUND

Cefiderocol is a new antibiotic used to treat infections with antibiotic resistant Gram-negative bacilli. The impact of differences between Mueller-Hinton agar (MHA) brands on susceptibility testing is underexplored. Compounding the implementation of cefiderocol susceptibility testing is a lack of harmonization between different regulatory body breakpoint criteria.

METHODS

We performed Kirby-Bauer disk diffusion using BD, Hardy, and Remel MHA, in addition to broth microdilution for Acinetobacter baumannii (n = 25), Enterobacterales (n = 25), Stenotrophomonas maltophilia (n = 24), and Pseudomonas aeruginosa (n = 23). We analyzed disk diffusion diameters and minimum inhibitory concentrations using interpretive criteria from the Clinical and Laboratory Standards Institute (CLSI), US Food and Drug Administration (FDA), and the European Committee on Antimicrobial Susceptibility Testing (EUCAST).

RESULTS

Breakpoint criteria impacted interpretation of susceptibly testing results, for example with the broth microdilution we found 8% (2/25) of A. baumannii isolates change interpretation between CLSI and EUCAST and 32% (8/25) change between CLSI and FDA, 12% (3/25) of Enterobacterales change between CLSI and EUCAST, 13% (3/23) of P. aeruginosa interpretations change between CLSI and FDA, and 4% (1/25) S. maltophilia change between CLSI and FDA. There was a significant difference between the zone disk diffusion diameters for P. aeruginosa and S. maltophilia between Hardy and BD; which changed interpretation (using CLSI criteria) for 8.7% (2/23) for P. aeruginosa but 0% (0/24) for S. maltophilia.

CONCLUSIONS

Breakpoint criteria impact cefiderocol susceptibility testing interpretation for broth microdilution and disk diffusion. Choice of MHA brand can also affect result interpretation.

Evaluation of the antimicrobial effects of Capsicum, Nigella sativa, Musa paradisiaca L., and Citrus limetta: A review

The extensive use of antibiotics and vaccines against microbial infections can result in long-term negative effects on humans and the environment. However, there are a number of plants that have antimicrobial effects against various disease-causing microbes such as bacteria, viruses, and fungi without negative side effects or harm to the environment. In this regard, four particular plants- Capsicum, Nigella sativa, Musa paradisiaca L., and Citrus limetta have been widely considered due to their excellent antimicrobial effect and ample availability. In this review, we discuss their antimicrobial effects due to the presence of thymoquinone, p-cymene, pinene, alkaloids, limonene, camphene, and melanin. These antimicrobial compounds disrupt the cell membrane of microbes, inhibit cellular division, and form biofilm in bacterial species, eventually reducing the number of microbes. Extraction of these compounds from the respective plants is carried out by different methods such as soxhlet, hydro-distillation, liquid-liquid extraction (LLE), pressurized liquid extraction (PLE), solid-phase extraction (SPE), supercritical fluid extraction (SFE), pulsed electric field (PEF), microwave-assisted extraction (MAE), enzyme-assisted extraction (EAE), ultrasound-assisted extraction (UAE), and high-voltage electrical discharge. Suitable selection of the extraction technique highly depends upon the associated advantages and disadvantages. In order to aid future study in this field, this review paper summarizes the advantages and disadvantages of each of these approaches. Additionally, the discussion covers how antimicrobial agents destroy harmful bacteria. Thus, this review offers in-depth knowledge to researchers on the antibacterial properties of Capsicum, Nigella sativa, Musa paradisiaca L. peels, and Citrus limetta.

Antimicrobial Activity of Ceftolozane-Tazobactam, Ceftazidime-Avibactam, and Cefiderocol against Multidrug-Resistant Pseudomonas aeruginosa Recovered at a German University Hospital

Multidrug-resistant (MDR) Pseudomonas aeruginosa increasingly causes health care-associated infections. In this study, we determined the activity of ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol against 223 MDR P. aeruginosa clinical isolates recovered from 2013 to 2017 at the University Hospital Frankfurt by using MIC test strips. Furthermore, we evaluated the presence of genes encoding major β-lactamases, such as VIM, IMP, NDM, GIM, SPM, and KPC; the extended spectrum β-lactamase (ESBL)-carbapenemase GES; and the virulence-associated traits ExoS and ExoU, as in particular ExoU is thought to be associated with poor clinical outcome. For MDR P. aeruginosa isolates, the MIC50/MIC90 values of ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol were 8/>256 mg/L, 16/>256 mg/L, and 0.25/1 mg/L, respectively. Cefiderocol showed the highest susceptibility rate (97.3%) followed by ceftazidime-avibactam (48.4%) and ceftolozane-tazobactam (46.6%). In 81 (36.3%) isolates, carbapenemase gene blaVIM was detected, and in 5 (2.2%) isolates, blaGES was detected (with a positive association of exoU and blaVIM). More than half of the isolates belong to the so-called international P. aeruginosa "high-risk" clones, with sequence type 235 (ST235) (24.7%) being the most prevalent. This study underlines that ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol are important options for the treatment of infections due to MDR P. aeruginosa, with cefiderocol currently being the most active available antipseudomonal β-lactam agent. According to our clinical experience, the outcome of cefiderocol therapy (8 patients) was favorable especially in cases of MDR P. aeruginosa-associated complicated urinary tract infections. IMPORTANCE After testing ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol against a collection of 233 multidrug-resistant (MDR) Pseudomonas aeruginosa, we showed that cefiderocol is the most active antipseudomonal β-lactam agent (susceptibility rates were 46.6%, 48.4%, and 97.4%, respectively). The most prevalent one was sequence type 235 (ST235) (24.7%), followed by ST244, ST175, and ST233, with all belonging to the top 10 P. aeruginosa high-risk clones with worldwide distribution. Our data indicate that during surveillance studies special attention should be paid to the MDR and highly virulent VIM- and ExoU-producing variant of ST235. Furthermore, in the case of infections caused by carbapenemase-producing MDR P. aeruginosa, cefiderocol is the preferred treatment option, while outcomes of complicated urinary tract infections and hospital-acquired pneumonia with cefiderocol were favorable.

Antibacterial spectrum of cefiderocol

Cefiderocol, a siderophore catechol cephalosporin, recently introduced in the market has been developed to enhance the in vitro activity of extended spectrum cephalosporins and to avoid resistance mechanisms affecting cephalosporins and carbapenems. The in vitro study of cefiderocol in the laboratory requires iron depleted media when MIC values are determined by broth microdilution. Disk diffusion presents good correlation with MIC values. In surveillance studies and in clinical trials it has been demonstrated excellent activity against Gram-negatives, including carbapenemase producers and non-fermenters such as Pseudomonas aeruginosa, Acinetobacter baumannii and Stenotrophomonas maltophilia. Few cefiderocol resistant isolates have been found in surveillance studies. Resistance mechanisms are not directly associated with porin deficiency and or efflux pumps. On the contrary, they are related with gene mutations affecting iron transporters, AmpC mutations in the omega loop and with certain beta-lactamases such us KPC-variants determining also ceftazidime-avibactam resistance, certain infrequent extended-spectrum betalactamases (PER, BEL) and metallo-beta-lactamases (certain NDM variants and SPM enzyme).

Cefiderocol: EUCAST criteria for disc diffusion and broth microdilution for antimicrobial susceptibility testing

OBJECTIVES

The reproducibility of cefiderocol MIC determination using broth microdilution (BMD) in iron-depleted CAMHB (ID-CAMHB) was investigated, and the EUCAST disc diffusion (DD) method for cefiderocol susceptibility testing was developed and validated against reference BMD.

METHODS

Cefiderocol values were determined for wild-type (WT) and non-WT isolates using BMD plates with ID-CAMHB (Thermo Scientific, Oakwood, USA) per EUCAST guidelines. DD was performed using standard EUCAST methodology on unsupplemented Mueller-Hinton agar with cefiderocol 30 μg discs. Control agents were included in all tests. MICs were correlated with zone diameters (ZD), and ZD breakpoints (BP) best corresponding to the MIC BPs were determined. Areas of technical uncertainty (ATU) were included where appropriate. External laboratory validation of cefiderocol DD was performed per the EUCAST SOP 9.2.

RESULTS

MIC and ZD distributions for cefiderocol against WT isolates were established. Cefiderocol ZD BPs were set at susceptible ≥22 mm, resistant <22 mm for Enterobacterales and Pseudomonas aeruginosa and ATUs were decided. For Acinetobacter baumannii and Stenotrophomonas maltophilia, ZD cut-off values of ≥17 mm and ≥20 mm corresponded to MIC values of ≤2 and ≤0.5 mg/L, respectively. Cefiderocol ZDs for Escherichia coli ATCC 25922 (target 27 mm) and P. aeruginosa ATCC 27853 (target 26 mm) were within ±3 mm of the target values. For DD, there was no problematic variation between discs, media or laboratories.

CONCLUSIONS

DD is a robust and easy-to-perform method for cefiderocol susceptibility testing. For isolates with results in the ATU, an MIC test should be performed to confirm the results.

Cefiderocol for the Treatment of Multidrug-Resistant Gram-Negative Bacteria: A Systematic Review of Currently Available Evidence

Cefiderocol is a novel synthetic siderophore-conjugated antibiotic that hijacks the bacterial iron transport systems facilitating drug entry into cells, achieving high periplasmic concentrations. This systematic review analyzed the currently available literature on cefiderocol. It summarized in vitro susceptibility data, in vivo antimicrobial activity, pharmacokinetics/pharmacodynamics (PK/PD), clinical efficacy, safety and resistance mechanisms of cefiderocol. Cefiderocol has potent in vitro and in vivo activity against multidrug-resistant (MDR) Gram-negative bacteria, including carbapenem-resistant isolates. But New Delhi Metallo-β-lactamase (NDM)- positive isolates showed significantly higher MICs than other carbapenemase-producing Enterobacterales, with a susceptible rate of 83.4% for cefiderocol. Cefiderocol is well-tolerated, and the PK/PD target values can be achieved using a standard dose regimen or adjusted doses according to renal function. Clinical trials demonstrated that cefiderocol was non-inferiority to the comparator drugs in treating complicated urinary tract infection and nosocomial pneumonia. Case reports and series showed that cefiderocol was a promising therapeutic agent in carbapenem-resistant infections. However, resistant isolates and reduced susceptibility during treatment to cefiderocol have already been reported. In conclusion, cefiderocol is a promising powerful weapon for treating MDR recalcitrant infections.

Treatment of Severe Infections Due to Metallo-Betalactamases Enterobacterales in Critically Ill Patients

Metallo-beta-lactamases-producing (MBL) Enterobacterales is a growing problem worldwide. The optimization of antibiotic therapy is challenging. The pivotal available therapeutic options are either the combination of ceftazidime/avibactam and aztreonam or cefiderocol. Colistin, fosfomycin, tetracyclines and aminoglycosides are also frequently effective in vitro, but are associated with less bactericidal activity or more toxicity. Prior to the availability of antibiotic susceptibility testing, severe infections should be treated with a combination therapy. A careful optimization of the pharmacokinetic/pharmacodynamic properties of antimicrobials is instrumental in severe infections. The rules of antibiotic therapy are also reported and discussed. To conclude, treatment of severe MBL infections in critically ill patients is difficult. It should be individualized with a close collaboration of intensivists with microbiologists, pharmacists and infection control practitioners.

Iron metabolism in bacterial cells: from physiological significance to a new class of antimicrobial agents

Infectious complications in the respiratory tract caused by microorganisms from the Burkholderia cepacia complex are the main cause of death among patients with cystic fibrosis. Natural and acquired resistance mechanisms allow Burkholderia cepacia complex pathogens to adapt to the conditions of regular antibiotic therapy, which necessitates the use of antibacterial drugs with an alternative mechanism of action. Studies on the importance of iron as an essential factor in the metabolism of bacteria and methods of its acquisition from the environment contributed to the development of a new antibiotic from a number of cephalosporins – cefiderocol. In the structure of cefiderocol, a fragment is formed that imitates siderophores – chelating molecules that ensure the transport of iron ions into the internal environment of the microorganism. A unique mechanism, described in the scientific literature as a “Trojan horse”, allows antibiotic molecules conjugated with siderophores to effectively penetrate into the bacterial cell, exerting a bactericidal effect. Thus, cefiderocol can be used to treat infectious complications in the lungs of patients with cystic fibrosis caused by bacteria from the Burkholderia cepacia complex, including multidrug-resistant strains. In addition, the spectrum of activity of cefiderocol allows the use of this antibiotic in the treatment of infections caused by nosocomial gram-negative bacteria such as Enterobacterales, Acinetobacter, Pseudomonas and Stenotrophomonas.

Cefiderocol: An Overview of Its in-vitro and in-vivo Activity and Underlying Resistant Mechanisms

Treatment of multidrug-resistant (MDR) Gram-negative bacteria (GNB) infections has led to a global public health challenging due to the bacterial resistance and limited choices of antibiotics. Cefiderocol (CFDC), a novel siderophore cephalosporin possessed unique drug delivery systems and stability to β-lactamases, has the potential to become first-line therapy for most aggressive MDR Gram-negative pathogens infection. However, there have been reports of drug resistance in the course of using CFDC. This study provides an overview of the in-vitro and in-vivo activity of CFDC and potential resistance mechanism was also summarized. In general, CFDC shows excellent activity against a broad range of MDR GNB pathogens including Enterobacteriaceae, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia. The expressions of metallo-β-lactamases such as inosine 5'-monophosphate (IMP), Verona integron-mediated metallo-β-lactamase (VIM), and New Delhi metallo-β-lactamase (NDM) are associated with a higher resistance rate of CFDC. Carbapenem-resistant phenotype has little effect on the resistance rate, although the acquisition of a particular carbapenemase may affect the susceptibility of the pathogens to CFDC. For potential resistance mechanism, mutations in β-lactamases and TonB-dependent receptors, which assist CFDC entering bacteria, would increase a minimum inhibitory concentration (MIC)90 value of CFDC against MDR pathogens. Since the development of CFDC, resistance during its utilization has been reported thus, prudent clinical applications are still necessary to preserve the activity of CFDC.

In Vitro Antimicrobial Activity of the Siderophore Cephalosporin Cefiderocol against Acinetobacter baumannii Strains Recovered from Clinical Samples

BACKGROUND

Cefiderocol is a siderophore cephalosporin that exhibits antimicrobial activity against most multi-drug resistant Gram-negative bacteria, including Enterobacterales, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia.

METHODS

A total of 20 multidrug-resistant A. baumannii strains were isolated from 2020 to 2021, molecularly characterized and tested to assess the in vitro antibacterial activity of cefiderocol. Thirteen strains were carbapenem-hydrolysing oxacillinase OXA-23-like producers, while seven were non-OXA-23-like producers. Minimum inhibitory concentrations (MICs) were determined by broth microdilution, considered as the gold standard method. Disk diffusion test was also carried out using iron-depleted CAMHB plates for cefiderocol.

RESULTS

Cefiderocol MICs ranged from 0.5 to 1 mg/L for OXA-23-like non-producing A. baumannii strains and from 0.25 to >32 mg/L for OXA-23-like producers, using the broth microdilution method. Cefiderocol MIC₉₀ was 8 mg/L. Diameter of inhibition zone of cefiderocol ranged from 18 to 25 mm for OXA-23-like non-producers and from 15 to 36 mm for OXA-23-like producers, using the diffusion disk method. A large variability and a low reproducibility were observed during the determination of diameter inhibition zone. Molecular characterization showed that all isolates presented the ISAba1 genetic element upstream the blaOXA-51. Among OXA-23-like non-producers, four were blaOXA-58 positive and two were negative for all the resistance determinants analyzed.

CONCLUSIONS

Cefiderocol showed in vitro antimicrobial activity against both carbapenem-susceptible and non-susceptible A. baumannii strains, although some OXA-23-like producers were resistant. Further clinical studies are needed to consolidate the role of cefiderocol as an antibiotic against MDR A. baumannii.

Contribution of PER-Type and NDM-Type β-Lactamases to Cefiderocol Resistance in Acinetobacter baumannii

Cefiderocol (FDC) is a recently developed siderophore cephalosporin showing excellent antibacterial activity against Gram-negative bacteria, including Acinetobacter baumannii. By investigating a series of A. baumannii clinical isolates with elevated MICs of FDC, we showed that PER-like β-lactamases and, to a lesser extent, NDM-like β-lactamases, significantly contributed to reduced susceptibility to that antibiotic. Interestingly, we showed that combination of FDC with avibactam exhibited excellent activity against all multidrug-resistant isolates coproducing OXA-23 and PER-type β-lactamases.

Cefiderocol: A Review in Serious Gram-Negative Bacterial Infections

Intravenous cefiderocol (Fetroja®; Fetcroja®) is the first siderophore cephalosporin approved for the treatment of adults with serious Gram-negative bacterial infections. Cefiderocol is stable against all four Ambler classes of β-lactamases (including metallo-β-lactamases) and exhibits excellent in vitro activity against many clinically relevant Gram-negative pathogens, including multidrug resistant strains. In randomized, double-blind clinical trials, cefiderocol was noninferior to imipenem/cilastatin for the treatment of complicated urinary tract infections (cUTI) and to meropenem for nosocomial pneumonia. Furthermore, in a pathogen-focused clinical trial in patients with carbapenem-resistant (CR) infections, cefiderocol showed comparable efficacy to best available therapy (BAT), albeit all-cause mortality rate was higher in the cefiderocol arm, the cause of which has not been established. Cefiderocol had a good tolerability and safety profile in clinical trials. Thus cefiderocol is a novel, emerging, useful addition to the current treatment options for adults with susceptible Gram-negative bacterial infections (including cUTI and nosocomial pneumonia) for whom there are limited treatment options.

Therapeutic Options for Metallo-β-Lactamase-Producing Enterobacterales

The spread of metallo-β-lactamase (MBL)-producing Enterobacterales worldwide without the simultaneous increase in active antibiotics makes these organisms an urgent public health threat. This review summarizes recent advancements in diagnostic and treatment strategies for infections caused by MBL-producing Enterobacterales. Adequate treatment of patients infected with MBL-producing Enterobacterales relies on detection of the β-lactamase in the clinic. There are several molecular platforms that are currently available to identify clinically relevant MBLs as well as other important serine-β-lactamases. Once detected, there are several antibiotics that have historically been used for the treatment of MBL-producing Enterobacterales. Antimicrobials such as aminoglycosides, tetracyclines, fosfomycin, and polymyxins often show promising in vitro activity though clinical data are currently lacking to support their widespread use. Ceftazidime-avibactam combined with aztreonam is promising for treatment of infections caused by MBL-producing Enterobacterales and currently has the most clinical data of any available antibiotic to support its use. While cefiderocol has displayed promising activity against MBL-producing Enterobacterales in vitro and in preliminary clinical studies, further clinical studies will better shed light on its place in treatment. Lastly, there are several promising MBL inhibitors in the pipeline, which may further improve the treatment of MBL-producing Enterobacterales.

Cefiderocol Antimicrobial Susceptibility Testing against Multidrug-Resistant Gram-Negative Bacilli: a Comparison of Disk Diffusion to Broth Microdilution

Antimicrobial susceptibility testing (AST) of cefiderocol poses challenges because of its unique mechanism of action (i.e., requiring an iron-depleted state) and due to differences in interpretative criteria established by the Clinical and Laboratory Standards Institute (CLSI), U.S. Food and Drug Administration (FDA), and European Committee on Antimicrobial Susceptibility Testing (EUCAST). Our objective was to compare cefiderocol disk diffusion methods (DD) to broth microdilution (BMD) for AST of Gram-negative bacilli (GNB). Cefiderocol AST was performed on consecutive carbapenem-resistant Enterobacterales (CRE; 58 isolates) and non-glucose-fermenting GNB (50 isolates) by BMD (lyophilized panels; Sensititre; Thermo Fisher) and DD (30 μg; research-use-only [RUO] MASTDISCS and FDA-cleared HardyDisks). Results were interpreted using FDA (prior to 28 September 2020 update), EUCAST, and investigational CLSI breakpoints (BPs). Categorical agreement (CA), minor errors (mE), major errors (ME), and very major errors (VME) were calculated for DD methods. The susceptibilities of all isolates by BMD were 72% (FDA), 75% (EUCAST) and 90% (CLSI). For DD methods, EUCAST BPs demonstrated lower susceptibility at 65% and 66%, compared to 74% and 72% (FDA) and 87% and 89% (CLSI) by HardyDisks and MASTDISCS, respectively. CA ranged from 75% to 90%, with 8 to 25% mE, 0 to 19% ME, and 0 to 20% VME and varied based on disk, GNB, and BPs evaluated. Both DD methods performed poorly for Acinetobacter baumannii complex. There is considerable variability when cefiderocol ASTs are interpreted using CLSI, FDA, and EUCAST breakpoints. DD offers a convenient alternative approach to BMD methods for cefiderocol AST, with the exception of A. baumannii complex isolates.

Cefiderocol Antimicrobial Susceptibility Testing Considerations: the Achilles' Heel of the Trojan Horse?

Cefiderocol (formerly S-649266) is a novel siderophore-conjugated cephalosporin with activity against a broad array of multidrug-resistant (MDR), aerobic Gram-negative bacilli. The siderophore component binds iron and uses active iron transport for drug entry into the bacterial periplasmic space. The cephalosporin moiety is the active antimicrobial component, structurally resembling a hybrid between ceftazidime and cefepime. Like other β-lactam agents, the principal bactericidal activity of cefiderocol occurs via inhibition of bacterial cell wall synthesis by binding of penicillin-binding proteins (PBPs) and inhibiting peptidoglycan synthesis, leading to cell death. Iron concentrations need to be taken into consideration when in vitro antimicrobial susceptibility to cefiderocol is determined. Broth microdilution (BMD) and disk diffusion methods have been developed to determine in vitro activity of cefiderocol. For BMD, cation-adjusted Mueller-Hinton broth (CAMHB) requires iron depletion to provide MICs predictive of in vivo activity. A method to prepare iron-depleted CAMHB (ID-CAMHB) has been described by the Clinical and Laboratory Standards Institute (CLSI). For disk diffusion, standard Mueller-Hinton agar is recommended, presumably because iron is bound in the medium. Currently, clinical FDA and European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints and investigational (research-use-only) CLSI breakpoints exist for interpreting cefiderocol susceptibility results for certain Gram-negative bacilli. Cefiderocol does not have clinically relevant activity against Gram-positive or anaerobic organisms. FDA or EUCAST breakpoints should be applied to interpret results for Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter baumannii complex for patient care until the investigational status has been removed from CLSI breakpoints. Further clinical outcome data are required to assess the effectiveness of cefiderocol for treatment of other Acinetobacter species (non-baumannii complex) and Stenotrophomonas maltophilia at this time, and, as such, antimicrobial susceptibility testing of these organisms should be limited to research use in the scenario of limited treatment options.