Clinical impact of rapid susceptibility testing on MHR-SIR directly from blood cultures

Rapid diagnostic of multidrug-resistant sepsis pathogens directly from blood culture bottles using MALDI-TOF and the EUCAST RAST

In this study, rapid diagnostic of multidrug-resistant (MDR) sepsis pathogens, directly from positive blood culture (BC) bottles, was evaluated by combining MALDI-TOF and the EUCAST Rapid Antimicrobial Susceptibility Testing (RAST). Carbapenemase production in Escherichia coli and Klebsiella pneumoniae isolates was also evaluated by RAST. From 171 positive BC bottles analyzed, 79 (46 %) MDR species, including E. coli (4/34, 12 %), K. pneumoniae (33/48, 69 %), Pseudomonas aeruginosa (12/12, 100 %), Acinetobacter baumannii (15/15, 100 %), and Staphylococcus aureus (14/37, 38 %) displaying resistance to beta-lactams, fluoroquinolones, aminoglycosides, and/or trimethoprim/sulphamethoxazole, were identified. In this regard, turnaround time of direct MALDI-TOF identification and RAST was < 7 h, which was significantly (p< 0.05) lower than our routine method. Carbapenemase detection by RAST displayed 100% sensitivity and 88.7 % specificity at 8 h. This protocol could offer advantages for the treatment and clinical outcomes of septic patients, improving the rapid diagnostic of sepsis by MDR pathogens.

Effect of rapid cefpodoxime disk screening for early detection of third-generation cephalosporin resistance in Escherichia coli and Klebsiella pneumoniae bacteremia

BACKGROUND

Several methods have been reported for detecting resistance genes or phenotypic testing on the day of positive blood culture in Escherichia coli or Klebsiella pneumoniae bacteremia. However, some facilities have not introduced these methods because of costs or other reasons. Toyota Kosei Hospital introduced cefpodoxime (CPDX) rapid screening on May 7, 2018, to enable early detection of third-generation cephalosporin resistance. In this study, we aimed to evaluate the effects of intervention with an Antimicrobial Stewardship Team using CPDX rapid screening.

METHODS

Cefotaxime (CTX)-resistant E. coli or K. pneumoniae bacteremia cases were selected retrospectively and divided into two groups: the pre-CPDX screening (June 1, 2015, to May 6, 2018) and CPDX screening groups (July 7, 2018, to August 31, 2021). The primary outcome was the proportion of cases in which modifications were made to the administration of susceptible antimicrobial agents within 24 h of blood culture-positive reports.

RESULTS

Overall, 63 patients in the pre-CPDX screening group and 84 patients in the CPDX screening group were eligible for analysis. The proportion of patients who modified to susceptible antimicrobial agents within 24 h of blood culture-positive reports was significantly increased in the CPDX screening group compared to that in the pre-CPDX screening group (6.3% vs. 22.6%, p = 0.010).

CONCLUSION

The results demonstrated that in CTX-resistant E. coli or K. pneumoniae bacteremia, CPDX rapid screening increased the proportion of early initiation of appropriate antimicrobial agents.

Multicentre Evaluation of the EUCAST Rapid Antimicrobial Susceptibility Testing (RAST) Extending Analysis to 16-20 Hours Reading Time

The aim of the study was to evaluate the EUCAST RAST method by extending analysis to 16−20 h reading time and performance with new β-lactam/β-lactamase inhibitor combinations. A total of 676 positive blood cultures (BCs) were enrolled. Results at 4 h, 6 h, 8 h and 16−20 h were interpreted according to bacterial species using EUCAST RAST breakpoints (version 5.1). For species for which no breakpoints were available, tentative breakpoints were used. Categorical agreement with the Microscan microdilution system was analysed. Among the 676 BCs enrolled, 641 were monomicrobial and were included in the analysis. Categorical agreement ranged from 98.9% at 4 h to 99.4% at 16−20 h. The rates of very major errors were 3.3%, 3.7% and 3.4% at 4 h, 6 h and 8 h, respectively, and decreased to 1% at 16−20 h (p < 0.001). The number of major errors was low for each reading time (0.2% and 0.4% at 4 h and 6 h, respectively, and 0.3% at both 8 h and 16−20 h). The proportions of results in the area of technical uncertainty were 9.9%, 5.9%, 5% and 5.2% for readings at 4 h, 6 h, 8 h and 16−20 h, respectively. Tentative breakpoints proposed for Enterobacterales other than E.coli/K.pneumoniae and coagulase-negative staphylococci showed overall performances comparable to those observed for E. coli/K. pneumoniae and S. aureus. In conclusion, EUCAST RAST has been shown to be reliable to determine microbial susceptibility to main antimicrobials, including ceftazidime/avibactam and ceftolozane/tazobactam. A poorer performance was observed for certain species/antimicrobial agent combinations. The better performance observed at 16−20 h compared to the early readings may confer to the method greater potential for antimicrobial de-escalation interventions.

Evaluation of an Antibiotic Susceptibility Testing Method on Enterobacterales-Positive Blood Cultures in Less Than 8 h Using the Rapid Mueller-Hinton Diffusion Method in Conjunction with the SIRscan 2000 Automatic Reading Device

Enterobacterales bloodstream infections are life-threatening and require rapid, targeted antibiotherapy based on antibiotic susceptibility testing (AST). A new method using Muller-Hinton Rapid-SIR (MHR-SIR) agar (i2a, Montpellier, France) allows complete direct AST (dAST) to be read from positive blood culture bottles (BCBs) for all Enterobacterales species after 6-8 h of incubation. We evaluated (i) the performance of dAST from positive BCBs on MHR-SIR agar using two different inoculum protocols; (ii) the categorical agreement between dAST results obtained with MHR-SIR agar vs. those obtained with Muller-Hinton (MH) agar; and (iii) the ability of the MHR-SIR medium to detect β-lactam resistant Enterobacterales. Finally, we estimated the saved turnaround time (TAT) with MHR-SIR compared with MH agar in our 24/7 laboratory. Our results showed that the most suitable inoculation protocol for dAST on MHR-SIR agar was 1 drop of BCB/5 mL H₂O. For monomicrobial Enterobacterales BCBs, dAST performed on MHR-SIR medium showed 99.3% categorical agreement with AST on MH agar. Furthermore, MHR-SIR agar allows early detection of β-lactam resistance mechanisms, including AmpC hyperproduction, extended-spectrum β-lactamase, and carbapenemase. Finally, TAT reduction in our 24/7 laboratory was 16 h, enabling a significantly faster provision of antibiotic advice.

Recent Developments in Phenotypic and Molecular Diagnostic Methods for Antimicrobial Resistance Detection in Staphylococcus aureus: A Narrative Review

Staphylococcus aureus is an opportunistic pathogen responsible for a wide range of infections in humans, such as skin and soft tissue infections, pneumonia, food poisoning or sepsis. Historically, S. aureus was able to rapidly adapt to anti-staphylococcal antibiotics and become resistant to several classes of antibiotics. Today, methicillin-resistant S. aureus (MRSA) is a multidrug-resistant pathogen and is one of the most common bacteria responsible for hospital-acquired infections and outbreaks, in community settings as well. The rapid and accurate diagnosis of antimicrobial resistance in S. aureus is crucial to the early initiation of directed antibiotic therapy and to improve clinical outcomes for patients. In this narrative review, I provide an overview of recent phenotypic and molecular diagnostic methods for antimicrobial resistance detection in S. aureus, with a particular focus on MRSA detection. I consider methods for resistance detection in both clinical samples and isolated S. aureus cultures, along with a brief discussion of the advantages and the challenges of implementing such methods in routine diagnostics.

Assessment of version 2.5 of QMAC-dRAST for rapid antimicrobial susceptibility testing with reduced sample-to-answer turnaround time and an integrated expert system

OBJECTIVE

To assess the performance of the new rapid antimicrobial susceptibility testing (AST) QMAC-dRAST V2.5 system.

METHODS

ASTs were performed using QMAC-dRAST-V2.5 and a disk diffusion method, directly from positive blood bottles with Gram-negative bacteria. Discrepancies between the results obtained using the two methods were categorized into very major errors (VME, S with dRAST vs. R with disk diffusion), major errors (ME, R vs. S, respectively), minor errors (mE, S vs. I or I vs. R, respectively), and very minor errors (Vme, I vs. S or R vs. I, respectively). For each AST, results were recorded after 4, 5, and 6h of incubation.

RESULTS

From 106 bacteremia, 1416 individual AST results were obtained. Overall agreement between results using the two methods was 91%, ranging from 76.9% to 99.1% depending upon the antibiotic, with 128 errors, i.e. 14/1416 (1%) VME, 59/1416 (4.2%) ME, 25/1416 (1.8%) mE and 30/1416 (2.1%) Vme. VMEs were encountered for Klebsiellasp and Serratia marcescens isolates with low-level piperacillin and amikacin resistance, respectively. Using the integrated QMAC-dRAST-V2.5 expert system, all 14 VMEs and 3 mEs were eliminated, leading to 92.2% categorical agreement. After 45min of pre-incubation in the QMAC-dRAST-V2.5 device, 22.2% of the 1416 AST results were obtained after 4h, an additional 31.4% after 5h and a further 46.3% after 6h.

CONCLUSION

QMAC-dRAST-V2.5 is an optimized version of QMAC-dRAST V2.0, particularly with respect to utilization of an expert system and reduced TAT according to the antibiotic tested.

Evaluation of the European Committee on Antimicrobial Susceptibility Testing Guidelines for Rapid Antimicrobial Susceptibility Testing of Bacillus anthracis-, Yersinia pestis- and Francisella tularensis-Positive Blood Cultures

Rapid determination of bacterial antibiotic susceptibility is important for proper treatment of infections. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) has recently published guidelines for rapid antimicrobial susceptibility testing (RAST) performed directly from positive blood culture vials. These guidelines, however, were only published for a limited number of common pathogenic bacteria. In this study, we evaluated the applicability of these guidelines to three Tier 1 bioterror agents (Bacillus anthracis, Yersinia pestis and Francisella tularensis) that require prompt antibiotic treatment to mitigate morbidity and mortality. We used spiked-in human blood incubated in a BACTEC™ FX40 system to determine the proper conditions for RAST using disc-diffusion and Etest assays. We found that reliable disc-diffusion inhibition diameters and Etest MIC values could be obtained in remarkably short times. Compared to the EUCAST-recommended disc-diffusion assays that will require adjusted clinical breakpoint tables, Etest-based RAST was advantageous, as the obtained MIC values were similar to the standard MIC values, enabling the use of established category breakpoint tables. Our results demonstrate the promising applicability of the EUCAST RAST for B. anthracis-, Y. pestis- or F. tularensis-positive blood cultures, which can lead to shorter diagnostics and prompt antibiotic treatment of these dangerous pathogens.

Rapid versus standard antimicrobial susceptibility testing to guide treatment of bloodstream infection

BACKGROUND

Rapid antimicrobial susceptibility tests are expected to reduce the time to clinically important results of a blood culture. This might enable clinicians to better target therapy to a person's needs, and thereby, improve health outcomes (mortality, length of hospital stay), and reduce unnecessary prescribing of broad-spectrum antibiotics; thereby reducing antimicrobial resistance rates.

OBJECTIVES

To assess the effects of rapid susceptibility testing versus standard susceptibility testing for bloodstream infections (BSIs).

SEARCH METHODS

To identify studies with selected outcomes, we searched the Cochrane Infectious Diseases Group Specialised Register, CENTRAL, MEDLINE, LILACS, and two trials registries, between 1987 and October 2020. We used 'bloodstream infection' and 'antimicrobial susceptibility tests' as search terms. We had no language or publication status limitations.

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing rapid antimicrobial susceptibility testing (with a time-to-result of ≤ 8 hours) versus conventional antimicrobial susceptibility testing in people with a BSI caused by any bacteria, as identified by a positive blood culture.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened references, full-text reports of potentially relevant studies, extracted data from the studies, and assessed risk of bias. Any disagreement was discussed and resolved with a third review author. For mortality, a dichotomous outcome, we extracted the number of events in each arm, and presented a risk ratio (RR) with 95% confidence interval (CI) to compare rapid susceptibility testing to conventional methods. We used Review Manager 5.4 to meta-analyse the data. For other outcomes, which are time-to-event outcomes (time-to-discharge from hospital, time-to-first appropriate antibiotic change), we conducted qualitative narrative synthesis, due to heterogeneity of outcome measures.  MAIN RESULTS: We included six trials, with 1638 participants. For rapid antimicrobial susceptibility testing compared to conventional methods, there was little or no difference in mortality between groups (RR 1.10, 95% CI 0.82 to 1.46; 6 RCTs, 1638 participants; low-certainty evidence). In subgroup analysis, for rapid genotypic or molecular antimicrobial susceptibility testing compared to conventional methods, there was little or no difference in mortality between groups (RR 1.02, 95% CI 0.69 to 1.49; 4 RCTs, 1074 participants; low-certainty evidence). For phenotypic rapid susceptibility testing compared to conventional methods, there was little or no difference in mortality between groups  (RR 1.37, 95% CI 0.80 to 2.35; 2 RCTs, 564 participants; low-certainty evidence). In qualitative analysis, rapid susceptibility testing may make little or no difference in time-to-discharge (4 RCTs, 1165 participants; low-certainty evidence). In qualitative analysis, rapid genotypic susceptibility testing compared to conventional testing may make little or no difference in time-to-appropriate antibiotic (3 RCTs, 929 participants; low-certainty evidence). In subgroup analysis, rapid phenotypic susceptibility testing compared to conventional testing may improve time-to-appropriate antibiotic (RR -17.29, CI -45.05 to 10.47; 2 RCTs, 564 participants; low-certainty evidence).  AUTHORS' CONCLUSIONS: The theoretical benefits of rapid susceptibility testing have not been demonstrated to directly improve mortality, time-to-discharge, or time-to-appropriate antibiotic in these randomized studies. Future large prospective studies should be designed to focus on the most clinically meaningful outcomes, and aim to optimize blood culture pathways.

Rapid Detection of Methicillin-Resistant Staphylococcus aureus Directly from Blood for the Diagnosis of Bloodstream Infections: A Mini-Review

Staphylococcus aureus represents a major human pathogen able to cause a number of infections, especially bloodstream infections (BSI). Clinical use of methicillin has led to the emergence of methicillin-resistant S. aureus (MRSA) and MRSA-BSI have been reported to be associated with high morbidity and mortality. Clinical diagnosis of BSI is based on the results from blood culture that, although considered the gold standard method, is time-consuming. For this reason, rapid diagnostic tests to identify the presence of methicillin-susceptible S. aureus (MSSA) and MRSA isolates directly in blood cultures are being used with increasing frequency to rapidly commence targeted antimicrobial therapy, also in the light of antimicrobial stewardship efforts. Here, we review and report the most common rapid non-molecular and molecular methods currently available to detect the presence of MRSA directly from blood.

Impact of Rapid Antimicrobial Susceptibility Testing in Gram-Negative Rod Bacteremia: a Quasi-experimental Study

Clinical justification for rapid antimicrobial susceptibility testing (AST) in Gram-negative rod (GNR) bacteremia is compelling; however, evidence supporting its value is sparse. We investigated the impact of rapid AST on clinical and antimicrobial stewardship outcomes in real-world practice. We performed a before-and-after quasi-experimental study from February 2018 to July 2019 at a tertiary hospital of the 24-h/day, 7-day/week implementation of the direct Vitek 2 AST method from positive blood culture broth for GNR bacteremia with electronic isolate-specific de-escalation comments and daytime antibiotic stewardship program (ASP) intervention. The primary outcome was time to appropriate antibiotic escalation or de-escalation, and secondary outcomes included time to oral antibiotic stepdown, hospital length of stay (LOS), all-cause 30-day mortality, 7-day incidence of acute kidney injury (AKI), and 30-day incidence of Clostridioides difficile infection (CDI). A total of 671 GNR isolates were included from 643 adult patients. Among patients for whom antibiotic change occurred after rapid AST result, rapid AST was associated with a trend in decreased time to escalation or de-escalation (hazard ratio, 1.22; 95% confidence interval [CI], 0.99 to 1.51; P = 0.06), with median times of 52.3 versus 42.2 h. Secondary outcomes were similar in both groups and include median time to oral antibiotic stepdown, LOS, all-cause mortality, and incidence of AKI and CDI. Rapid AST led to improved stewardship measures but did not impact clinical patient outcomes. These results highlight that multiple variables in addition to the timing of the AST result contribute to clinical outcome and that further intervention may be required to clinically justify rapid AST implementation.

Comparative evaluation of the QMAC-dRAST V2.0 system for rapid antibiotic susceptibility testing of Gram-negative blood culture isolates

To comparatively evaluate the performance of the rapid antimicrobial susceptibility testing (AST) system QMAC-dRAST V2.0 and of standard disk diffusion in agar, AST was performed directly from 100 positive blood culture bottles with Gram-negative bacilli. AST results provided by QMAC-dRAST showed 92.9% agreement with disk diffusion method results. Discrepancies observed between results obtained with QMAC-dRAST and disk diffusion method conducted to 10 very major errors (0.8%, S with QMAC-dRAST vs R with disk diffusion method), 40 major errors (3.2%, R vs S, respectively), 15 minor errors (1.2%, S vs I or I vs R, respectively) and 23 very minors errors (1.8%, I vs S or R vs I, respectively). For very major and major errors, in only 36% of the cases did the repeat QMAC-dRAST confirm the initial result, whereas a repeat AST using disk diffusion method confirmed the initial result in 92% of cases. AST results obtained using microdilution in liquid medium confirmed those obtained with QMAC-dRAST and disk diffusion method in 4% and 89%, respectively. Repeatability and reproducibility tests performed on QMAC-dRAST using reference strains showed 94% to 100% of R/S/I categorical agreement.

Evaluation of EUCAST rapid antimicrobial susceptibility testing (RAST) for positive blood cultures in clinical practice using a total lab automation

Our objective was to evaluate EUCAST’s ‘rapid antimicrobial susceptibility testing’ (RAST) directly from positive blood culture that delivers antimicrobial results within 6 h for Staphylococcus aureus, Enterococcus spp., Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa, using total lab automation. Zone diameters from RAST were compared with MIC results. Furthermore, its influence on time to report was investigated. RAST was performed to all positive aerobic and anaerobic blood culture bottles by subculturing them, i.e. onto Mueller-Hinton agar and adding six antibiotic discs covering Gram-negative and Gram-positive therapy (cefoxitin, ampicillin, vancomycin, piperacillin/tazobactam, meropenem and ciprofloxacin). RAST was automatically imaged after 6 h. Zone sizes were measured using a TLA software tool and interpreted according to EUCAST clinical breakpoints. Bacteria were identified using MALDI-TOF MS and MIC results were determined using Vitek2 panels. Categorial agreement between agar diffusion and MIC results was investigated. Additionally, time to RAST and time to Vitek were compared for 100 isolates (20 per species). Between November 2018 and April 2019, 3313 positive mono-bacterial blood culture bottles were collected of which 894 bottles with RAST-validated species were investigated. Among these bottles, 2029 individual antibiotic measurements were compared with MIC results from Vitek2 and 14 very major, 28 major and 12 minor errors were found. A median reduction of 17:30 h in time to report was observed. Introduction of RAST with automatic TLA imaging function could reduce time to report by 17:30 h. Excellent accordance between zone diameter and MIC results, particularly for cefoxitin, vancomycin and meropenem, was observed, but drawbacks due to ATU were seen.

Clinical impact of rapid susceptibility testing on Mueller-Hinton Rapid-SIR directly from urine specimens

Urinary tract infection diagnosis and management generally involves a 48-h microbiological delay to obtain the antibiotic susceptibility test (AST) results. In the context of multidrug resistance, reducing the time to obtain AST results is an essential factor, allowing for more timely appropriate treatment. We conducted a single-centre prospective study on urinary samples meeting two criteria: significant leukocyturia > 50/mm³ and exclusive presence of Gram-negative bacilli on direct examination. AST were performed by direct inoculation on Mueller-Hinton Rapid-SIR (MHR-SIR) agar. We evaluated the time to antibiotic adaptation by the antimicrobial stewardship team according to rapid AST results. Patients were subsequently excluded from the study if asymptomatic bacteria were confirmed, or in the absence of clinical data. Seventy patients were included. Mean age of patients was 68.8 years (± 21.3). Empirical antibiotic treatment were mainly based on third generation cephalosporins (n = 33), fluoroquinolones (n = 15), beta-lactamin/beta-lactamase inhibitors (n = 7), fosfomycin and nitrofurantoin (n = 5, each). The average time to obtain results was 7.2 h (± 1.6 h). Adaptation of therapy following MHR-SIR was performed for 29 patients (41%) with early switch to oral antibiotics, de-escalation or escalation in respectively 72.3%, 30%, and 11% of cases. Time saving of MHR-SIR compared with the standard technique was 42.6 (± 16.7) h. This study showed that rapid antibiotic susceptibility test results, using MHR-SIR method directly from urine, can be obtained 40 h earlier than conventional AST. The study also demonstrated significant clinical impact on the selection and reduction of the antibiotic therapy spectrum.