Comparison of 3 diagnostic platforms for identification of bacteria and yeast from positive blood culture bottles

Clinical evaluation of an in-house Xpert Lysate-based Method combined with MALDI-TOF MS for the rapid identification of positive blood cultures

BACKGROUND

In clinical practice, bloodstream infections (BSIs) can lead to a very high mortality rate. Rapid identification (ID) of the pathogenic bacteria in positive blood cultures (PBCs) can guide the clinical implementation of effective antibiotic treatment in advance, thereby helping to reduce the mortality rate.

METHODS

Using the Conventional Culture Method results as criteria, we evaluated the effectiveness of our newly developed in-house method, the Xpert Lysate-based Method, for rapidly identifying pathogens in PBCs across four hospitals.

RESULTS

A total of 629 monomicrobial PBCs were investigated. The Xpert Lysate-based Method correctly identified 96.18% of PBCs at the species level and 97.30% at the genus level. When the confidence scores of MALDI-TOF MS were ≥ 2.000, ≥ 1.700, and ≥ 1.500, the percentages of correctly identified PBCs at the species level were 67.47%, 94.24%, and 98.88%, respectively. When the score threshold of species-level ID was set to 1.500, the rates reached 98.25% for Gram-positives (GPs), 93.54% for Gram-negatives (GNs), 70.00% for anaerobes, and 94.74% for fungi, respectively. The median confidence score of ≥ 2.000 indicated high certainty in identifying common BSI pathogens. Additionally, one of the microbial species was correctly identified in 10 out of 11 PBCs with polymicrobial growth. The entire operation process took an average of 10 min of hands-on time and 15 to 20 min for time-to-result.

CONCLUSION

The method of directly identifying microbial pellets using MALDI-TOF MS, extracted via the Xpert Lysate-based Method we developed, is non-inferior to the conventional Culture Method in terms of ID performance. Meanwhile, it is easy to operate and more time-efficient, making it suitable for routine workflow in the rapid etiological ID of PBCs.

Comparative Assessment of Rapid Identification and Antimicrobial Susceptibility Testing Methods for Bloodstream Infections in a Non-24/7 Clinical Microbiology Laboratory

Rapid identification and antimicrobial susceptibility testing are essential for timely bloodstream infection (BSI) management. This study aimed to investigate the performance and turnaround time of multiple rapid diagnostic methods in a microbiology laboratory without 24/7 operation. This study included 236 positive blood culture bottles. Rapid identification methods were assessed with the SepsiTyper kit and the FilmArray blood culture identification 2 (BCID2) panel. Rapid antimicrobial susceptibility testing (AST) methods involved direct AST using the BD Phoenix M50 system and QuantaMatrix direct and rapid antimicrobial susceptibility testing (dRAST) and resistance gene detection with the FilmArray BCID2 panel. Conventional methods were used to compare results. The turnaround time was analyzed from blood culture positivity to preparation initiation and from preparation initiation to result reporting. Both rapid identification methods significantly reduced the turnaround time (~1 day and 19 h) compared to conventional identification. SepsiTyper demonstrated higher species-level accuracy in monomicrobial samples, whereas BCID2 outperformed in polymicrobial cases. Among the rapid AST methods, BCID2 and dRAST enabled result reporting within 24 h of positivity. Preparation delays were >45% of the overall turnaround time. Rapid diagnostics substantially shortened the BSI diagnostic time, even in limited-operation settings. Their clinical utility may be improved through 24/7 laboratory workflows.

Performance of molecular tests for diagnosis of bloodstream infections in the clinical setting: a systematic literature review and meta-analysis

BACKGROUND

Rapid identification of bloodstream pathogens and associated antimicrobial resistance (AMR) profiles by molecular tests from positive blood cultures (PBCs) have the potential to improve patient management and clinical outcomes.

OBJECTIVES

A systematic review and meta-analysis were conducted to evaluate diagnostic test accuracy (DTA) of molecular tests from PBCs for detecting pathogens and AMR in the clinical setting.

METHODS

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DATA SOURCES

Medline, Embase, Cochrane, conference proceedings, and study bibliographies were searched.

STUDY ELIGIBILITY CRITERIA

Studies evaluating DTA of commercially available molecular tests vs. traditional phenotypic identification and susceptibility testing methods in patients with PBCs were eligible.

PARTICIPANTS

Patients with PBCs.

TESTS

Commercially available molecular tests.

REFERENCE STANDARD

Traditional phenotypic identification and susceptibility testing methods (standard of care, SOC).

ASSESSMENT OF RISK OF BIAS

Study quality was assessed using Quality Assessment of Diagnostic Accuracy Studies-2.

METHODS OF DATA SYNTHESIS

Summary DTA outcomes were estimated using bivariate random-effects models for gram-negative bacteria (GNB), gram-positive bacteria (GPB), yeast, GNB-AMR, GPB-AMR, and specific targets when reported by ≥ 2 studies (PROSPERO CRD42023488057).

RESULTS

Seventy-four studies including 24 590 samples were analysed, most of which had a low risk of bias. When compared with SOC, molecular tests showed 92-99% sensitivity, 99-100% specificity, 99-100% positive predictive value, and 97-100% negative predictive value for identifying total GNB (43 studies), GPB (38 studies), yeast (24 studies), GNB-AMR (35 studies), and GPB-AMR (39 studies). For individual pathogen targets, 93-100% sensitivity, 98-100% specificity, 86-100% positive predictive value, and 99-100% negative predictive value were estimated. Five of seven AMR genes had 91-99% sensitivity and 99-100% specificity. Sensitivity was lower for IMP (four studies; 62%; 95% CI, 34-83%) and VIM (four studies; 70%; 95% CI, 38-90%) carbapenemases, where genes were not detected or were not harboured in Pseudomonas aeruginosa (i.e. low prevalence). Performance of molecular tests in detecting AMR was generally comparable when grouped by geographical region (Europe, North America, and East Asia).

DISCUSSION

High DTA support the use of molecular tests in identifying a broad panel of pathogens and detecting AMR in GNB and GPB.

Getting Up to Speed: Rapid Pathogen and Antimicrobial Resistance Diagnostics in Sepsis

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Time to receive effective therapy is a primary determinant of mortality in patients with sepsis. Blood culture is the reference standard for the microbiological diagnosis of bloodstream infections, despite its low sensitivity and prolonged time to receive a pathogen detection. In recent years, rapid tests for pathogen identification, antimicrobial susceptibility, and sepsis identification have emerged, both culture-based and culture-independent methods. This rapid narrative review presents currently commercially available approved diagnostic molecular technologies in bloodstream infections, including their clinical performance and impact on patient outcome, when available. Peer-reviewed publications relevant to the topic were searched through PubMed, and manufacturer websites of commercially available assays identified were also consulted as further sources of information. We have reviewed data about the following technologies for pathogen identification: fluorescence in situ hybridization with peptide nucleic acid probes (Accelerate PhenoTM), microarray-based assay (Verigene®), multiplex polymerase chain reaction (cobas® eplex, BioFire® FilmArray®, Molecular Mouse, Unyvero BCU SystemTM), matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (Rapid MBT Sepsityper®), T2 magnetic resonance (T2Bacteria Panel), and metagenomics-based assays (Karius©, DISQVER®, Day Zero Diagnostics). Technologies for antimicrobial susceptibility testing included the following: Alfed 60 ASTTM, VITEK® REVEALTM, dRASTTM, ASTar®, Fastinov®, QuickMIC®, ResistellTM, and LifeScale. Characteristics, microbiological performance, and issues of each method are described, as well as their clinical performance, when available.