Evaluation of the Accelerate Pheno™ system for rapid identification and antimicrobial susceptibility testing of Gram-negative bacteria in bloodstream infections

An improved protocol for bacteria identification by MALDI-TOF MS directly from positive blood cultures

FASTinov® developed a rapid antimicrobial susceptibility test that includes the purification of a bacterial suspension directly from positive blood cultures (BC). In order to streamline laboratory workflow, the use of the bacterial suspension obtained through FASTinov® sample prep was tested for identification (ID) by matrix absorption laser deionization-time of flight mass spectrometry (MALDI-TOF MS) (Bruker) in 364 positive BC, and its accuracy assessed comparing with the MALDI-TOF MS ID of the next-day subcultured colonies. FASTinov sample prep was highly reliable for rapid ID directly from BC with proportion of agreement of 94.9% for Gram-positive and 96.3% for Gram-negative bacteria.

Antimicrobial Multidrug Resistance: Clinical Implications for Infection Management in Critically Ill Patients

The increasing incidence of antimicrobial resistance (AMR) worldwide represents a serious threat in the management of sepsis. Due to resistance to the most common antimicrobials prescribed, multidrug-resistant (MDR) pathogens have been associated with delays in adequate antimicrobial therapy leading to significant increases in mortality, along with prolonged hospital length of stay (LOS) and increases in healthcare costs. In response to MDR infections and the delay of microbiological results, broad-spectrum antibiotics are frequently used in empirical antimicrobial therapy. This can contribute to the overuse and misuse of antibiotics, further promoting the development of resistance. Multiple measures have been suggested to combat AMR. This review will focus on describing the epidemiology and trends concerning MDR pathogens. Additionally, it will explore the crucial aspects of identifying patients susceptible to MDR infections and optimizing antimicrobial drug dosing, which are both pivotal considerations in the fight against AMR. Expert commentary: The increasing AMR in ICUs worldwide makes the empirical antibiotic therapy challenging in septic patients. An AMR surveillance program together with improvements in MDR identification based on patient risk stratification and molecular rapid diagnostic tools may further help tailoring antimicrobial therapies and avoid unnecessary broad-spectrum antibiotics. Continuous infusions of antibiotics, therapeutic drug monitoring (TDM)-based dosing regimens and combination therapy may contribute to optimizing antimicrobial therapy and limiting the emergence of resistance.

Clinical impact of the accelerate PhenoTest® BC system on patients with gram-negative bacteremia and high risk of antimicrobial resistance: a prospective before-after implementation study

BACKGROUND

The Accelerate PhenoTest® BC system (AXDX) is a novel assay for rapid bacterial identification and antimicrobial susceptibility (AST). We report an evaluation of its impact on treatment of patients with Gram-negative bacteremia (GNB) with a high risk of antimicrobial resistance (AMR).

METHODS

A prospective single-center evaluation before and after implementation of AXDX in addition to standard-of-care (SOC) microbiology and antimicrobial stewardship program (ASP). Patients with GNB reported during laboratory working hours and prespecified risk factors for AMR were included. The primary outcome was an ASP-oriented beneficial antimicrobial change, defined as either an escalation of an inappropriate empiric treatment or de-escalation of a broad-spectrum treatment of a susceptible organism. Main secondary outcomes were time to an appropriate treatment, antimicrobial treatment duration, length of stay (LOS) and mortality.

RESULTS

Included were 46 and 57 patients in the pre- and post-intervention periods, respectively. The median time to an AST-oriented beneficial change was 29.2 h vs. 49.6 h, respectively (p < 0.0001). There were no significant differences in the time to appropriate treatment, LOS or mortality. Antimicrobial treatment duration was longer during the intervention period (10 vs. 8 days, p = 0.007). AXDX failed to correctly identify pathogens in all 6 cases of polymicrobial bacteremia. In two cases patient care was potentially compromised due to inappropriate de-escalation.

CONCLUSIONS

AXDX implementation resulted in a 20.4-hour shorter time to an ASP-oriented beneficial antimicrobial change. This should be weighed against the higher costs, the lack of other proven clinical benefits and the potential harm from mis-identification of polymicrobial bacteremias.

Performance of a System for Rapid Phenotypic Antimicrobial Susceptibility Testing of Gram-Negative Bacteria Directly from Positive Blood Culture Bottles

The rapid administration of optimal antimicrobial treatment is paramount for the treatment of bloodstream infections (BSIs), and rapid antimicrobial susceptibility testing (AST) results are essential. Q-linea has developed the ASTar system, a rapid phenotypic AST device. Here, we report the performance of the ASTar BC G- (Gram-negative) kit when assessed according to the ISO 20776-2:2007 standard for performance evaluation of in vitro diagnostic AST devices. The evaluated ASTar BC G- kit uses a broad panel of 23 antimicrobials for the treatment of BSIs caused by Gram-negative fastidious and nonfastidious bacteria across a range of 6 to 14 2-fold dilutions, including cefoxitin as a screening agent for AmpC-producing Enterobacterales. The ASTar system processes blood culture samples to generate data on MICs and susceptible, intermediate, or resistant (SIR) category. The automated protocol includes concentration determination and concentration adjustment to enable a controlled inoculum, followed by broth microdilution (BMD) and microscopy performed continuously to generate MIC values within approximately 6 h once the test is run on the ASTar system. The performance of the ASTar system was assessed against the ISO 20776-2:2007 standard BMD reference method. Testing was performed across three sites, with results from 412 contrived blood cultures and 74 fresh clinical blood cultures. The ASTar system was also tested for reproducibility, with triplicate testing of 11 strains. The accuracy study comprised 8,650 data points of bacterium-antimicrobial tests. The ASTar system demonstrated an overall essential agreement (EA) of 95.8% (8,283/8,650) and a categorical agreement (CA) of 97.6% (8,433/8,639) compared to the reference BMD method. The overall rate of major discrepancies (MDs) was 0.9% (62/6,845), and that of very major discrepancies (VMDs) was 2.4% (30/1,239). This study shows that the ASTar system delivers reproducible results with overall EA and CA of >95%.

SERS-based antibiotic susceptibility testing: Towards point-of-care clinical diagnosis

Emerging antibiotic resistant bacteria constitute one of the biggest threats to public health. Surface-enhanced Raman scattering (SERS) is highly promising for detecting such bacteria and for antibiotic susceptibility testing (AST). SERS is fast, non-destructive (can probe living cells) and it is technologically flexible (readily integrated with robotics and machine learning algorithms). However, in order to integrate into efficient point-of-care (PoC) devices and to effectively replace the current culture-based methods, it needs to overcome the challenges of reliability, cost and complexity. Recently, significant progress has been made with the emergence of both new questions and new promising directions of research and technological development. This article brings together insights from several representative SERS-based AST studies and approaches oriented towards clinical PoC biosensing. It aims to serve as a reference source that can guide progress towards PoC routines for identifying antibiotic resistant pathogens. In turn, such identification would help to trace the origin of sporadic infections, in order to prevent outbreaks and to design effective medical treatment and preventive procedures.

The Accelerate Pheno™ System-A New Tool in Microbiological Diagnostics of Bloodstream Infections: A Pilot Study from Poland

The aim of this study was to evaluate the usefulness of the Accelerate Pheno™ system (APS) (Accelerate Diagnostics, Denver, CO, USA) for rapid laboratory diagnosis of bloodstream infections. The study included 45 positive blood samples obtained from patients hospitalized in University Hospital No. 1 in Bydgoszcz, Poland. In 40 (88.9%) blood samples, the APS was capable of identification of at least one microorganism at the genus or species level and in 38 (84.4%) of them additionally assessed antimicrobial susceptibility. The time of identification and the time to result of antimicrobial susceptibility ranged from 1:32 to 1:42 and 5:02 to 5:36 h, respectively. Six positive blood samples revealed a poly-microbial culture. In these cases, only one out of two or three microorganisms was detected by the APS, and the system assessed antimicrobial susceptibility only for them. For 78.6% positive blood samples, agreement on identification compared to mass spectrometry was found. For all but one sample, a 96-100% compliance of the resistance category was achieved when comparing the antimicrobial susceptibility testing results to conventional methods. Using the APS, the total time to report was reduced from 13:34 to even 63:47 h compared to the standard microbiological laboratory workflow. The APS is a very useful system, especially for the rapid assessment of antimicrobial susceptibility of bacteria directly from positive blood samples, offering the greatest potential for microbiology laboratories operating around the clock.

Paving the way for precise diagnostics of antimicrobial resistant bacteria

The antimicrobial resistance (AMR) crisis from bacterial pathogens is frequently emerging and rapidly disseminated during the sustained antimicrobial exposure in human-dominated communities, posing a compelling threat as one of the biggest challenges in humans. The frequent incidences of some common but untreatable infections unfold the public health catastrophe that antimicrobial-resistant pathogens have outpaced the available countermeasures, now explicitly amplified during the COVID-19 pandemic. Nowadays, biotechnology and machine learning advancements help create more fundamental knowledge of distinct spatiotemporal dynamics in AMR bacterial adaptation and evolutionary processes. Integrated with reliable diagnostic tools and powerful analytic approaches, a collaborative and systematic surveillance platform with high accuracy and predictability should be established and implemented, which is not just for an effective controlling strategy on AMR but also for protecting the longevity of valuable antimicrobials currently and in the future.

Real Life Clinical Impact of Antimicrobial Stewardship Actions on the Blood Culture Workflow from a Microbiology Laboratory

BACKGROUND

Accelerating the diagnosis of bacteremia is one of the biggest challenges in clinical microbiology departments. The fast establishment of a correct treatment is determinant on bacteremic patients' outcomes. Our objective was to evaluate the impact of antimicrobial therapy and clinical outcomes of a rapid blood culture workflow protocol in positive blood cultures with Gram-negative bacilli (GNB).

METHODS

A quasi-experimental before-after study was performed with two groups: (i) control group (conventional work-protocol) and (ii) intervention group (rapid workflow-protocol: rapid identification by Matrix-Assisted Laser Desorption/Ionization-Time-Of-Flight (MALDI-TOF) and antimicrobial susceptibility testing (AST) from bacterial pellet without overnight incubation). Patients were divided into different categories according to the type of intervention over treatment. Outcomes were compared between both groups.

RESULTS

A total of 313 patients with GNB-bacteremia were included: 125 patients in the control group and 188 in the intervention. The time from positive blood culture to intervention on antibiotic treatment decreased from 2.0 days in the control group to 1.0 in the intervention group (p < 0.001). On the maintenance of correct empirical treatment, the control group reported 2.0 median days until the clinical decision, while in the intervention group was 1.0 (p < 0.001). In the case of treatment de-escalation, a significant difference between both groups (4.0 vs. 2.0, p < 0.001) was found. A decreasing trend on the change from inappropriate treatments to appropriate ones was observed: 3.5 vs. 1.5; p = 0.12. No significant differences were found between both groups on 7-days mortality or on readmissions in the first 30-days.

CONCLUSIONS

Routine implementation of a rapid workflow protocol anticipates the report of antimicrobial susceptibility testing results in patients with GNB-bacteremia, decreasing the time to effective and optimal antibiotic therapy.

Concordance Between Antibiotic Resistance Genes and Susceptibility in Symptomatic Urinary Tract Infections

PURPOSE

Studies have shown that multiple genes influence antibiotic susceptibility, but the relationship between genotypic and phenotypic antibiotic susceptibility is unclear. We sought to analyze the concordance between the presence of antibiotic resistance (ABR) genes and antibiotic susceptibility results in urine samples collected from patients with symptomatic urinary tract infection (UTI).

PATIENTS AND METHODS

Urine samples were collected from patients presenting to 37 geographically disparate urology clinics across the United States from July 2018 to February 2019. Multiplex polymerase chain reaction was used to detect 27 ABR genes. In samples containing at least one culturable organism at a concentration of ≥ 104 cells per mL, pooled antibiotic susceptibility testing (P-AST), which involves simultaneous growing all detected bacteria together in the presence of antibiotic and then measure susceptibility, was performed against 14 antibiotics. The concordance rate between the ABR genes and the P-AST results was generated for the overall group. The concordance rates for each antibiotic between monomicrobial and polymicrobial infection were compared using chi-square test.

RESULTS

Results from ABR gene detection and P-AST of urine samples from 1155 patients were included in the concordance analysis. Overall, there was a 60% concordance between the presence or absence of ABR genes and corresponding antimicrobial susceptibility with a range of 49-78% across antibiotic classes. Vancomycin, meropenem, and piperacillin/tazobactam showed significantly lower concordance rates in polymicrobial infections than in monomicrobial infections.

CONCLUSION

Given the 40% discordance rate, the detection of ABR genes alone may not provide reliable data to make informed clinical decisions in UTI management. However, when used in conjunction with susceptibility testing, ABR gene data can offer valuable clinical information for antibiotic stewardship.

Rapid Antimicrobial Susceptibility Testing Methods for Blood Cultures and Their Clinical Impact

Antimicrobial susceptibility testing (AST) of bacteria isolated in blood cultures is critical for optimal management of patients with sepsis. This review describes new and emerging phenotypic and genotypic AST methods and summarizes the evidence that implementation of these methods can impact clinical outcomes of patients with bloodstream infections.

Performance evaluation of Alfred60AST rapid susceptibility testing directly from positive blood cultures in the routine laboratory workflow

The aim of this study was to evaluate the performance of the new automated system Alfred⁶⁰AST which is based on light scattering technology for rapid susceptibility testing directly from positive blood cultures as well as its applicability in the routine laboratory workflow. We evaluated 176 significant episodes of bacteremia due to 92 Gram-negative and 84 Gram-positive bacteria. The antimicrobial agents tested were ceftriaxone, ciprofloxacin, gentamicin, meropenem, piperacillin-tazobactam, and colistin for Gram negatives and cefoxitin, vancomycin, linezolid, and daptomycin for Gram positives. Concordance assessment was performed in comparison with our routine method, Vitek2 (bioMérieux). Discrepancies were resolved with MICRONAUT-S (Merlin) or E-test (bioMérieux). Out of 690 susceptibility determinations, 94.05% showed categorical agreement (CA) with the routine method and this percentage increased to 94.49 after discrepancy analysis. There were 1.45% very major errors, 3.33% major errors, and 1.16% minor errors (decreased to 1.45, 3.04, and 1.01 after discrepancy analysis). The CA for most of the antibiotics was above 90% except for daptomycin for Gram positives (87.30%) and ceftriaxone for Gram negatives (88.23%). The concordance was slightly better for Gram negative than for Gram-positive bacteria (94.30 versus 93.70%, respectively). The total turnaround time for a complete Alfred⁶⁰AST result was 6-6.5h. The evaluated method gave rapid and reliable results in a few hours, versus 48h for the conventional one. Implementing this technology in routine workflow allows clinicians to optimize the treatment on the same day of blood culture positivity with potential positive clinical benefits and impact on antibiotic stewardship.

Clinical and economical improvements after introducing rapid identification of bacteria and early antibiotic susceptibility testing in sepsis and bloodstream infections. Results of the PHENOMENON study

Background: Sepsis and bloodstream infections pose severe challenges in intensive care. Early reliable diagnosis is the key to successful therapy. The objective of the study presented here was to investigate the clinical and economical effects of the new Pheno^TM BC test, which allows bacteria identification (ID) and antimicrobial susceptibility testing (AST) in approximately 7 hours after a blood culture becomes positive (BC+). Methods: Historically controlled interventional study. Population: patients with BC+ and ICU admission. Inadequate initial antimicrobial therapy (IAT) is need of therapy change based on result. Prospectively the new test was used in addition. Primary endpoint: time-to-result in hours. Contribution margin (CM) i.e. revenue - costs was computed. All patients formed the intention-to-treat population (ITT). Patients with complete cost data formed the modified ITT group (mITT). CM results were calculated for mITT and PP. Further analyses: length-of-stay (LOS) and mortality. Results: 223 historical and 200 prospective patients were included. Time to result (ITT) was shortened by 51.1 hours (83 vs. 31.9; p<0.001). Overall savings (mITT) were 257,100 € (-301,264 € vs. -44,164 €). 143 of 181 (79%) patients had a test performed, 126 of 143 (88%) having a clinically useable result. 40 (32%) had IAT vs. 65 (29%) in the historic cohort. Median time to AST in PP was shortened by 61.7 hours (89.5 vs. 27.8; p<0.001). LOS was shortened 7 days (28 vs. 19; p=0.226) and mortality was 8% (40.5% vs. 32.5%; p=0.440) lower. Median CM +3,074.80 € per case (-2,350.50 € vs. +724.70 €; p=0.040). Conclusion: The new Pheno^TM ID+AST test leads to faster and clinically meaningful results and saves money by shortening LOS on the ICU.

Accelerate Pheno™ blood culture detection system: a literature review

Accelerate Pheno™ (ACC) is a fully automated system providing rapid identification of a panel of bacteria and yeasts, and antimicrobial susceptibility testing of common bacterial pathogens responsible for bloodstream infections and sepsis. Diagnostic accuracy for identification ranges from 87.9 to 100%, and antimicrobial susceptibility testing categorical agreement is higher than 91%. The present review includes peer-reviewed studies on ACC published to date. Both interventional and hypothetical studies evidenced the potential positive clinical role of ACC in the management and therapy of patients with bloodstream infections and sepsis, due to the important reduction in time to report, suggesting a crucial impact on the therapeutic management of these patients, provided the presence of a hospital antimicrobial stewardship program, a 24/7 laboratory operating time and a strict collaboration between clinical microbiologist and clinician. Further prospective multicenter studies are necessary to explore the impact of this system on mortality, length of stay and spread of multidrug-resistant organisms.

Modern Blood Culture: Management Decisions and Method Options

The optimal care of septic patients depends on the successful recovery of clinically relevant microorganisms from blood cultures and the timely reporting of organism identification and antimicrobial susceptibility testing (AST) results. Many preanalytic factors play a critical role in culturing microorganisms, and advancements in blood culture instrument technology have reduced the time to positive results. Additionally, rapid organism identification and AST results directly from positive blood culture broth via new methods help to further shorten the time from empiric to targeted treatment. This article summarizes the current state of blood culture methods, including preanalytic, analytical, and postanalytic factors that are available to clinical microbiology laboratories.

Modern Tools for Rapid Diagnostics of Antimicrobial Resistance

Fast, robust, and affordable antimicrobial susceptibility testing (AST) is required, as roughly 50% of antibiotic treatments are started with wrong antibiotics and without a proper diagnosis of the pathogen. Validated growth-based AST according to EUCAST or CLSI (European Committee on Antimicrobial Susceptibility Testing, Clinical Laboratory Standards Institute) recommendations is currently suggested to guide the antimicrobial therapy. Any new AST should be validated against these standard methods. Many rapid diagnostic techniques can already provide pathogen identification. Some of them can additionally detect the presence of resistance genes or resistance proteins, but usually isolated pure cultures are needed for AST. We discuss the value of the technologies applying nucleic acid amplification, whole genome sequencing, and hybridization as well as immunodiagnostic and mass spectrometry-based methods and biosensor-based AST. Additionally, we evaluate the potential of integrated systems applying microfluidics to integrate cultivation, lysis, purification, and signal reading steps. We discuss technologies and commercial products with potential for Point-of-Care Testing (POCT) and their capability to analyze polymicrobial samples without pre-purification steps. The purpose of this critical review is to present the needs and drivers for AST development, to show the benefits and limitations of AST methods, to introduce promising new POCT-compatible technologies, and to discuss AST technologies that are likely to thrive in the future.

Effective implementation of the Accelerate Pheno™ system for positive blood cultures

Using conventional methods, organism identification (ID) and antibiotic susceptibility testing (AST) results are available ∼1.5–3 days after positive blood culture. New technologies can reduce this time to 8–12 h, allowing therapy to be optimized substantially sooner. To make full use of fast ID and AST results requires overcoming various hurdles to effective implementation, including restructuring laboratory workflows to optimize timeliness of results and modifying clinical pathways to respond more quickly when results are available. Efficient laboratory procedures and clinical interventions coupled with fast and accurate identification and AST results have the potential to substantially reduce overall costs and provide more-sophisticated and effective patient management.

Clinical Impact of Accelerate PhenoTM Rapid Blood Culture Detection System in Bacteremic Patients

BACKGROUND

Accelerate Pheno blood culture detection system (AXDX) provides identification (ID) and antimicrobial susceptibility testing (AST) results within 8h of blood culture growth. Limited data exists regarding its clinical impact. Other rapid platforms coupled with antimicrobial stewardship program (ASP) real-time notification (RTN) have shown improved length of stay (LOS) in bacteremia.

METHODS

A single-center, quasi-experimental study of adult bacteremic inpatients before/after AXDX implementation was conducted comparing clinical outcomes from 1 historical and 2 intervention cohorts (AXDX and AXDX+RTN). Primary outcome was LOS.

RESULTS

Of 830 bacteremic episodes, 188 (77%) of 245 historical and 308 (155 AXDX, 153 AXDX+RTN; 65%) of 585 intervention episodes were included. Median LOS was shorter with AXDX (6.3d) and AXDX+RTN (6.7d) compared to historical (8.1d; P=0.001). Achievement of optimal therapy (AOT) was more frequent (93.6% and 95.4%) and median time to optimal therapy (TTOT) was faster (1.3d and 1.4d) in AXDX and AXDX+RTN compared to historical (84.6%, P≤0.001 and 2.4d; P≤0.001) respectively. Median antimicrobial days of therapy (DOT) was shorter in both intervention arms compared to historical (6d each vs 7d; P=0.011). Median LOS benefit was most pronounced in patients with coagulase negative Staphylococcus bacteremia (5.5d and 4.5d vs 7.2d; P=0.003) in AXDX, AXDX+RTN, and historical cohorts respectively.

CONCLUSIONS

LOS, AOT, TTOT, and total DOT significantly improved after AXDX implementation. Addition of RTN did not show further improvement over AXDX and an already active ASP. These results suggest AXDX can be integrated into healthcare systems with an active ASP even without the resources to include RTN.

A new culture-based method for rapid identification of microorganisms in polymicrobial blood cultures by MALDI-TOF MS

Background

The application of matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) to microbial identification has allowed the development of rapid methods for identification of microorganisms directly in positive, blood cultures (BCs). These methods can yield accurate results for monomicrobial BCs, but often fail to identify multiple microorganisms in polymicrobial BCs. The present study was aimed at establishing a rapid and simple method for identification of bacteria and yeast in polymicrobial BCs from patients with bloodstream infection.

Results

The rapid method herein proposed is based on short-term culture in liquid media allowing selective growth of microorganisms recovered from polymicrobial BCs, followed by rapid identification by MALDI-TOF MS. To evaluate the accuracy of this method, 56 polymicrobial BCs were comparatively analyzed with the rapid and routine methods. The results showed concordant identification for both microbial species in 43/50 (86%) BCs containing two different microorganisms, and for two microbial species in six BCs containing more than two different species. Overall, 102/119 (85.7%) microorganisms were concordantly identified by the rapid and routine methods using a cut-off value of 1.700 for valid identification. The mean time to identification after BC positivity was about 4.2 h for streptococci/enterococci, 8.7 h for staphylococci, 11.1 h for Gram-negative bacteria, and 14.4 h for yeast, allowing a significant time saving compared to the routine method.

Conclusions

The proposed method allowed rapid and reliable microbial identification in polymicrobial BCs, and could provide clinicians with timely, useful information to streamline empirical antimicrobial therapy in critically ill patients.

Evaluation of a new Rapid Antimicrobial Susceptibility system for Gram-negative and Gram-positive bloodstream infections: speed and accuracy of Alfred 60AST

BACKGROUND

Blood stream infections (BSIs) are a major cause of morbidity and mortality. The time from taking blood cultures to obtain results of antibiotic sensitivity can be up to five days which impacts patient care. The Alfred 60 AST™ can reduce laboratory time from positive culture bottle to susceptibility results from 16 to 25 h to 5-6 h, transforming patient care. To evaluate the diagnostic accuracy of a rapid antimicrobial susceptibility system, the Alfred 60 AST™, in clinical isolates from patients with BSIs and confirm time to results. 301 Gram-negative and 86 Gram-positive isolates were analysed directly from positive blood culture bottles following Gram staining. Antimicrobial susceptibility results and time-to-results obtained by rapid Alfred 60 AST system and BD Phoenix were compared .

RESULTS

A total of 2196 antimicrobial susceptibility test results (AST) were performed: 1863 Gram-negative and 333 Gram-positive. AST categorical agreement (CA) for Alfred 60 AST™ was 95% (1772/1863) for Gram-negative and 89% (295/333) for Gram-positive isolates. Gram-negative CA: ampicillin 96% (290/301); ciprofloxacin 95% (283/297); ceftriaxone 96% (75/78); meropenem 97% (288/297); piperacillin-tazobactam 95% (280/295); gentamicin 94% (279/297) and amikacin 93% (277/298). The median time to susceptibility results from blood culture flagging positive was 6.3 h vs 20 h (p < 0.01) for Alfred system vs BD Phoenix™.

CONCLUSION

Alfred 60 AST system greatly reduced time to antimicrobial susceptibility results in Gram-negative and Gram-positive BSIs with good performance and cost, particularly for Gram-negative bacteraemia.

Direct antimicrobial susceptibility testing of positive blood cultures: a comparison of the Accelerate Pheno™ and VITEK® 2 systems

OBJECTIVES

To compare the performance and time-to-result (TTR) for antimicrobial susceptibility testing (AST) of positive blood cultures (PBC) using the Accelerate Pheno™ system (AXDX) and both a direct VITEK® 2 card inoculation workflow (DV2) and traditional FDA-approved VITEK® 2 workflow using subcultured isolates (V2).

METHODS

Patient samples with monomicrobial Gram-negative rod bacteremia were tested on AXDX and DV2 in tandem and compared to V2 AST results. Categorical agreement (CA) errors were adjudicated using broth microdilution. Instrumentation times and AST TTR were compared.

RESULTS

AXDX and DV2 had a CA of 93.4% and 97.4%, respectively, compared to V2. Postadjudication, AXDX, DV2, and V2 had CA of 94.7%, 95.7%, and 96.5%, respectively. Instrument run times were 6.6 h, 9.4 h, and 9.2 h, and AST TTR were 8.9 h, 12.9 h and 35.5 h, respectively.

CONCLUSIONS

AXDX and DV2 ASTs are fast and reliable, which may have significant antimicrobial stewardship implications.

How to accelerate antimicrobial susceptibility testing

BACKGROUND

Antimicrobial susceptibility testing (AST) results are crucial for timely administration of effective antimicrobial treatment, and, thus, should be made available to clinicians as fast as possible. In particular, increasing rates of multidrug-resistant organisms emphasize the need for rapid AST (rAST).

OBJECTIVES

This article aims to provide microbiologists and clinicians with a critical overview of the current state of possibilities to accelerate AST. We also intend to discuss technical and strategic aspects of rAST, which may be helpful to academic researchers and assay developers in the industry.

SOURCES

We have reviewed literature on rAST methods and their implementation in routine diagnostics.

CONTENT

Phenotypic rAST is universal, mechanism-independent and allows exact categorization, but it demands time for the microorganisms to start the growth and to express the response to antibiotics. Detection of selected resistance mechanisms is more rapid, but the interpretation of its clinical impact is limited. Technical challenges of phenotypic rAST include inoculum effect, delayed expression of resistance, lag phase and initial biomass increase in susceptible isolates. Criteria for a successful rAST assay are ease of use, random access, capacity for simultaneous testing of multiple specimens, affordability and financial attractiveness for industry. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)-based AST seems to be particularly promising, as it can optimally be combined with MALDI-TOF MS identification. Direct testing from clinical specimens provides particularly early findings, with positive blood cultures being the most suitable specimen type. Polymicrobial samples and inoculum effect are serious obstacles for direct AST from other clinical specimens. Next to the technology improvement, optimization of pre-analytics and laboratory organization is essential.

IMPLICATIONS

It appears feasible to generate an AST report within the same working shift; however, only affordable and easy-to-use rAST technologies have a chance to enter broad diagnostic routine. Efforts should be made by industry, authorities and academia to enable wide dissemination of rAST in clinical diagnostics.

Susceptibility Provision Enhances Effective De-escalation (SPEED): utilizing rapid phenotypic susceptibility testing in Gram-negative bloodstream infections and its potential clinical impact

Objectives

We evaluated the performance and time to result for pathogen identification (ID) and antimicrobial susceptibility testing (AST) of the Accelerate Pheno™ system (AXDX) compared with standard of care (SOC) methods. We also assessed the hypothetical improvement in antibiotic utilization if AXDX had been implemented.

Methods

Clinical samples from patients with monomicrobial Gram-negative bacteraemia were tested and compared between AXDX and the SOC methods of the VERIGENE® and Bruker MALDI Biotyper® systems for ID and the VITEK® 2 system for AST. Additionally, charts were reviewed to calculate theoretical times to antibiotic de-escalation, escalation and active and optimal therapy.

Results

ID mean time was 21 h for MALDI-TOF MS, 4.4 h for VERIGENE® and 3.7 h for AXDX. AST mean time was 35 h for VITEK® 2 and 9.0 h for AXDX. For ID, positive percentage agreement was 95.9% and negative percentage agreement was 99.9%. For AST, essential agreement was 94.5% and categorical agreement was 93.5%. If AXDX results had been available to inform patient care, 25% of patients could have been put on active therapy sooner, while 78% of patients who had therapy optimized during hospitalization could have had therapy optimized sooner. Additionally, AXDX could have reduced time to de-escalation (16 versus 31 h) and escalation (19 versus 31 h) compared with SOC.

Conclusions

By providing fast and reliable ID and AST results, AXDX has the potential to improve antimicrobial utilization and enhance antimicrobial stewardship.

Laboratory automation reduces time to report of positive blood cultures and improves management of patients with bloodstream infection

The impact on time to results (TTR) and clinical decisions was evaluated for mono-microbial positive blood cultures (BC) processed using the BD Kiestra Work Cell Automation (WCA) system. Positive BC were processed by the WCA system by full-automatic subculture on solid media and digital imaging after 8 h of incubation (8-h method) followed by identification (ID) and antimicrobial susceptibility testing (AST). To evaluate the accuracy of the 8-h method, ID and AST from 8-h and overnight incubated colonies were compared for the same organisms. To evaluate its clinical impact, results from 102 BC processed by the 8-h method (cases) were compared with those from 100 BC processed by overnight incubation method (controls) in a comparable period. Identification after 8-h and overnight incubation gave concordant results in 101/102 (99.0%) isolates. Among a total of 1379 microorganism-antimicrobial combinations, categorical agreement was 99.4% (1371/1379); no very major error, 7 major errors, and one minor error were observed. TTR in cases (32.8 h ± 8.3 h) was significantly (p < 0.001) shorter than in controls (55.4 h ± 13.3 h). A significant reduction was observed for duration of empirical therapy (cases 54.8 h ± 23.3 h vs controls 86.9 h ± 34.1 h, p < 0.001) and 30-day crude mortality rate (cases 16.7% vs controls 29.0%, p < 0.037). Automation and 8-h digital reading of plates from positive BC, followed by ID and AST, greatly reduce TTR and shorten the duration of antimicrobial empiric therapy, possibly improving outcome in patients with mono-microbial bloodstream infections.