Developments for improved diagnosis of bacterial bloodstream infections

Cross-kingdom pathogen detection via duplex universal PCR and high-resolution melt

Infectious diseases caused by pathogenic bacteria and fungi continuously pose a significant threat worldwide. The occurrence of polymicrobial infections, including polybacterial, polyfungal or bacteria-fungal co-infections further complicates diagnosis and treatment. Current diagnostic methods, heavily reliant on culture methods, are slow and often inefficient. This inefficiency underscores the urgent need for new diagnostic approaches that can swiftly identify a wide array of pathogens across both the bacterial and fungal kingdoms. In response to this need, our study introduces a duplex universal PCR and high-resolution melt (HRM) method that enables the detection of both bacterial and fungal pathogens within a single PCR-HRM procedure. This method uses two universal primer sets designed to target bacterial and fungal genomic DNA respectively, facilitating broad-range detection of 16 pathogens flagged by the World Health Organization (WHO). Moreover, this assay can be adapted in microfluidic-based digital reaction format and when analyzed via a one-versus-one support vector machine classifier achieved a detection accuracy exceeding 99.9%. This digital duplex PCR-HRM method has the capacity to quantitatively detect co-infections with varying pathogen ratios in simulated samples, demonstrating its versatility and multiplexed capacity. When applied to clinical bronchoalveolar lavage (BAL) samples, digital duplex PCR-HRM successfully identified both monomicrobial and polymicrobial infections. This development marks a significant advancement in the field of infectious disease diagnostics, offering a rapid, accurate, and comprehensive method for identifying a broad spectrum of bacterial and fungal pathogens, thus potentially improving patient management and outcomes.

Rapid identification of pathogenic bacteria from clinical positive blood cultures via virus-like magnetic bead enrichment and MALDI-TOF MS profiling

Reducing the time required for the detection of bacteria in blood samples is a critical area of investigation in the field of clinical diagnosis. Positive blood culture samples often require a plate culture stage due to the interference of blood cells and proteins, which can result in significant delays before the isolation of single colonies suitable for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis. In this study, we developed a non-specific enrichment strategy based on SiO2-encapsulated Fe3O4 nanoparticles combined with MALDI-TOF MS for direct identification of bacteria from aqueous environments or positive blood culture samples. Three distinct types of Fe3O4@SiO2 magnetic nanoparticles (MNPs) with unique surface morphologies were developed: spherical MNPs with smooth surfaces (Fe3O4@SN), mesoporous silica coated MNPs (Fe3O4@MSN), and MNPs exhibiting a viral spiked structure (Fe3O4@VSN). These MNPs exhibited excellent binding affinity towards both Staphylococcus aureus and Klebsiella pneumoniae in PBS and artificial saliva solutions. Furthermore, the strategy of using Fe3O4@VSN, which involves non-specific interactions between bacterial cells and the virus-like surface, resulted in a dramatic reduction in the minimum detectable concentrations of target pathogens by up to 1000-fold compared to conventional methods. Our results demonstrate that the use of Fe3O4@VSN has the potential to significantly reduce the processing time required after blood culture and may be useful for enrichment and identification of microorganisms in complex clinical samples.

Enhancing pathogens detection in suspected geriatric bloodstream infections using Nanopore-targeted sequencing

Bloodstream infections (BSIs) are a critical concern for elderly patients, where prompt and accurate diagnosis is vital for effective treatment. Traditional blood culture methods suffer from delayed results and susceptibility to false-negatives. Nanopore-targeted sequencing (NTS) offers rapid pathogen detection and reporting, presenting a promising alternative. However, the application of NTS for diagnosing suspected BSIs in geriatric patients remains insufficiently studied. We conducted a retrospective cohort study from January 2022 to January 2024, including 198 geriatric patients suspected of BSIs. We utilized NTS to detect pathogen characteristics and compared the effectiveness and consistency of NTS with simultaneous blood culture testing for pathogen detection. NTS demonstrated a pathogen detection rate of 61.1%. The most common bacterial pathogens were Escherichia coli and Staphylococcus aureus (each 7.7%), while Candida albicans was the most prevalent fungal pathogen (30%). Mixed-bacterial infections were detected in 21.7% of NTS-positive cases, and concurrent bacterial-fungal infections were observed in 9.92% of these cases. NTS-positive patients had higher rates of comorbidities, elevated inflammatory markers, and worse prognoses compared to NTS-negative patients. NTS exhibited a significantly higher pathogen detection rate and faster turnaround time than blood culture (78.1% vs 42.2%, P < 0.001), with an agreement rate of 65.6%. The elderly BSI patients frequently involve multiple or mixed infections and correlate with poorer prognoses. NTS provides a faster and more sensitive diagnostic alternative to traditional blood culture, potentially improving clinical outcomes and guiding more effective treatment strategies. This study highlights the need for further research to validate the routine clinical integration of NTS for managing BSIs in geriatric populations.

IMPORTANCE

Bloodstream infections (BSIs) in elderly patients pose substantial diagnostic and therapeutic challenges due to the limitations of traditional blood culture methods, which are hampered by slow turnaround times and false-negatives. Nanopore-targeted sequencing (NTS) emerges as a significant advancement, offering rapid and accurate pathogen detection directly from blood samples. This study demonstrates that NTS provides a higher detection rate and faster results than conventional blood cultures, crucial for the timely management of BSIs in geriatric patients, who often present with multiple or mixed infections and have poorer clinical outcomes. The findings underscore the potential of NTS to enhance diagnostic accuracy and speed, informing more effective treatment strategies and improving overall patient outcomes. Further research is essential to establish NTS as a routine diagnostic tool in the clinical management of BSIs in the elderly.

Comparative evaluation of BacT/ALERT VIRTUO and BACTEC FX400 blood culture systems for the detection of bloodstream infections

Bloodstream infections (BSI) pose significant threats to patient health, necessitating timely and accurate diagnostics to reduce mortality and morbidity. This study aimed to evaluate the clinical performance of the BacT/ALERT VIRTUO blood culture system with FANPlus bottles compared to the BACTEC FX400 system in detecting bloodstream pathogens. A total of 1,772 blood specimens were collected from various hospital wards. Specimen selection criteria were based on clinical suspicion of bloodstream infections, ensuring the inclusion of relevant and representative patient samples. These blood samples, collected from the same suspected sepsis patients, were cultured in parallel using both the BacT/ALERT VIRTUO and BACTEC FX400 systems. The diagnostic efficiency of both systems, including detection rates, time to detection (TTD), and sensitivity across different bacterial species, was assessed. In various application scenarios, the VIRTUO system demonstrates a higher positive detection rate, whether in the intensive care unit (ICU) (8.5% vs 6.4%, P = 0.028) or in general wards. Additionally, for different types of bacteria, the TVIRTUO system exhibits superior detection rates for anaerobic bacteria (5.9% vs 3.2%, P < 0.001) and aerobic bacteria (9.1% vs 7.2%, P = 0.043). Furthermore, it boasts a shorter median TTD of 14 hours compared to 16 hours, and a higher sensitivity for Gram-positive bacteria (2.8% vs 1.6%, P < 0.001). These findings emphasize VIRTUO's effectiveness in enhancing diagnostic accuracy, achieving faster time to detection, and expanding the spectrum of detected organisms, thereby facilitating the quicker initiation of appropriate therapies, supporting precise clinical decision-making, and ultimately improving patient outcomes.IMPORTANCEOur study conducted a critical evaluation of advanced blood culture technologies for managing bloodstream infections (BSI). A distinctive strength of our research is the large sample size and the concurrent testing of the same patients with two systems, a methodology rarely achieved in other studies. BSIs present severe health threats, necessitating prompt and accurate diagnostics to mitigate morbidity and mortality. The BacT/ALERT VIRTUO system, in comparison to the BACTEC FX400 system, demonstrated superior detection capabilities, emphasizing the critical role of advanced diagnostics in clinical settings.

Risk factors of bloodstream infection in erythroderma from atopic dermatitis, psoriasis, and drug reactions: a retrospective observational cohort study

Background

Atopic dermatitis (AD), psoriasis, and drug reactions associated with erythroderma are frequently complicated by infections. However, bloodstream infection (BSI) have received less research attention.

Objectives

This study aimed to investigate the clinical characteristics and risk factors associated with BSI in patients with erythroderma.

Methods

A retrospective analysis was conducted on 141 erythroderma cases. Eleven cases were identified as having BSI. Clinical records of both BSI and non-BSI groups were reviewed and compared.

Results

BSI was diagnosed in 7.80% (11/141) of erythroderma cases, with a breakdown of 7.14% in AD, 2.00% in psoriasis, and 17.14% in drug reactions. Notably, all positive skin cultures (7/7) showed bacterial isolates concordant with blood cultures. Univariate logistic regression analysis revealed several significant associations with BSI, including temperature (≤36.0 or ≥38.5 °C; odds ratio (OR) = 28.06; p < 0.001), chilling (OR = 22.10; p < 0.001), kidney disease (OR = 14.64; p < 0.001), etiology of drug reactions (OR = 4.18; p = 0.03), albumin (ALB) (OR = 0.86; p < 0.01), C-reaction protein (CRP) (OR = 1.01; p = 0.02), interleukin 6 (IL-6) (OR = 1.02; p = 0.02), and procalcitonin (PCT) (OR = 1.07; p = 0.03). Receiver operating characteristic (ROC) curves demonstrated significant associations with ALB (p < 0.001; the area under curve (AUC) = 0.80), PCT (p = 0.009; AUC = 0.74), and CRP (p = 0.02; AUC = 0.71).

Conclusions

Increased awareness of BSI risk is essential in erythroderma management. Patients with specific risk factors, such as abnormal body temperature (≤36.0 or ≥38.5 °C), chilling sensations, kidney disease, a history of drug reactions, elevated CRP (≥32 mg/L), elevated PCT (≥1.00 ng/ml), and low albumin (≤31.0 g/L), require close monitoring for BSI development.

Distinguishing Gram-positive and Gram-negative bloodstream infections through leukocytes, C-reactive protein, procalcitonin, and D-Dimer: an empirical antibiotic guidance

This retrospective study aimed to compare the difference of the levels of white blood cells (WBC), C-reactive protein (CRP), procalcitonin, and D-Dimer in the bloodstream infection (BSI) patients, and their values in distinguishing bacterial categories. A total of 847 BSI patients were analysed and divided into Gram-positive BSI (GP-BSI) and Gram-negative BSI (GN-BSI) groups. Most frequently isolated pathogens in GP-BSI were Staphylococcus epidermidis (35.75%), followed by Staphylococcus hominis (18.33%), and Streptococcus haemolyticus (10.16%), while in GN-BSI, Escherichia coli (30.07%), Klebsiella pneumoniae (23.98%), and Acinetobacter baumannii (13.18%) were the most common. The predictive value was evaluated based on 3 years of patient data, which showed an area under the curve (AUC) of 0.828. It was further validated using 2 years of data, which yielded an AUC of 0.925. Significant differences existed in the procalcitonin, D-Dimer, and CRP levels between GN-BSI and GP-BSI. The current results provide a more effective strategy for early differential diagnosis in bacterial categorization of BSI when combining WBC, CRP, procalcitonin, and D-Dimer measurements.

Antibacterial Activity of Boron Compounds Against Biofilm-Forming Pathogens

This study aimed to evaluate the antibacterial activity of nine boron derivatives against biofilm-forming pathogenic bacteria. The effect of boron derivatives (CMB, calcium metaborate; SMTB, sodium metaborate tetrahydrate; ZB, zinc borate; STFB, sodium tetra fluorine borate; STB, sodium tetraborate; PTFB, potassium tetra fluor borate; APTB, ammonium pentabo-rate tetrahydrate; SPM, sodium perborate monohydrate; Borax, ATFB, ammonium tetra fluorine borate) on bacteria isolated from blood culture was determined by the minimum inhibitory concentration (MIC) method. Then, biofilm formation potentials on microplates, tubes, and Congo red agar were examined. The cytotoxicity of boron derivatives was determined by using WST-1-based methods. The interaction between the biofilm-forming bacteria, fibroblast cells, and boron derivatives was determined with the infection model. We found that the sodium metaborate tetrahydrate molecule was effective against all pathogens. According to the optical density values detected at 630 nm in microplates, meticillin-resistant Staphylococcus aureus was observed to have the most substantial biofilm ability at 0.257 nm. As a result of cytotoxicity studies, it has been determined that a 1 µg/L concentration of boron derivatives is not toxic to fibroblast L929 cells. In cell culture experiments, these boron derivatives have very serious inhibitory activity against biofilm-forming pathogens in a short treatment period, such as 2-4 h. Furthermore, using these molecules on inanimate surfaces affected by biofilms would be appropriate instead of living cells.

Development of an Optically Induced Dielectrophoresis (ODEP) Microfluidic System for High-Performance Isolation and Purification of Bacteria

For the rapid detection of bacteria in a blood sample, nucleic acid amplification-based assays are believed to be promising. Nevertheless, the nucleic acids released from the dead blood cells or bacteria could affect the assay performance. This highlights the importance of the isolation of live bacteria from blood samples. To address this issue, this study proposes a two-step process. First, a blood sample was treated with the immuno-magnetic microbeads-based separation to remove the majority of blood cells. Second, an optically induced dielectrophoresis (ODEP) microfluidic system with an integrated dynamic circular light image array was utilized to further isolate and purify the live bacteria from the remaining blood cells based on their size difference. In this work, the ODEP microfluidic system was developed. Its performance for the isolation and purification of bacteria was evaluated. The results revealed that the method was able to harvest the live bacteria in a high purity (90.5~99.2%) manner. Overall, the proposed method was proven to be capable of isolating and purifying high-purity live bacteria without causing damage to the co-existing cells. This technical feature was found to be valuable for the subsequent nucleic-acid-based bacteria detection, in which the interferences caused by the nontarget nucleic acids could be eliminated.

Metagenomic Sequencing of Positive Blood Culture Fluid for Accurate Bacterial and Fungal Species Identification: A Pilot Study

With blood stream infections (BSIs) representing a major cause of mortality and morbidity worldwide, blood cultures play a crucial role in diagnosis, but their clinical application is dampened by the long turn-around time and the detection of only culturable pathogens. In this study, we developed and validated a shotgun metagenomics next-generation sequencing (mNGS) test directly from positive blood culture fluid, allowing for the identification of fastidious or slow growing microorganisms more rapidly. The test was built based on previously validated next-generation sequencing tests, which rely on several key marker genes for bacterial and fungal identification. The new test utilizes an open-source metagenomics CZ-ID platform for the initial analysis to generate the most likely candidate species, which is then used as a reference genome for downstream, confirmatory analysis. This approach is innovative because it takes advantage of an open-source software's agnostic taxonomic calling capability while still relying on the more established and previously validated marker gene-based identification scheme, increasing the confidence in the final results. The test showed high accuracy (100%, 30/30) for both bacterial and fungal microorganisms. We further demonstrated its clinical utility especially for anaerobes and mycobacteria that are either fastidious, slow growing, or unusual. Although applicable in only limited settings, the Positive Blood Culture mNGS test provides an incremental improvement in solving the unmet clinical needs for the diagnosis of challenging BSIs.

Simultaneous determination of procalcitonin and interleukin-6 in human serum samples with a point-of-care biosensing device

The simultaneous determination of two inflammatory diseases biomarkers, namely procalcitonin (PCT) and interleukin-6 (IL-6), in human serum samples employing a Point-of-Care device based on Multi Area Reflectance Spectroscopy is presented. Dual-analyte detection was achieved using silicon chips with two silicon dioxide areas of different thickness, one functionalized with an antibody specific for PCT and the other with an antibody specific for IL-6. The assay included reaction of immobilized capture antibodies with mixtures of PCT and IL-6 calibrators with the biotinylated detection antibodies, streptavidin and biotinylated-BSA. The reader provided for the automated execution of the assay procedure, as well as for the collection and processing of the reflected light spectrum, the shift of which is correlated to analytes concentration in the sample. The assay was completed in 35 min and the detection limits for PCT and IL-6 were 2.0 and 0.01 ng/mL respectively. The dual-analyte assay was characterized by high reproducibility (the intra- and inter-assay coefficients of variation were less than 10% for both analytes) and accuracy (the percent recovery values ranged from 80 to 113% for both analytes). Moreover, the values determined for the two analytes in human serum samples with the assay developed were in good agreement with the values determined for the same samples by clinical laboratory methods. These results support the potential of the proposed biosensing device application for inflammatory biomarkers determination at the Point-of-Need.

BIOFIRE® Blood Culture IDentification 2 (BCID2) panel for early adaptation of antimicrobial therapy in adult patients with bloodstream infections: a real-life experience

Our objective was to assess the effectiveness of a multiplex PCR panel for blood culture identification (BCID2) on the implementation of appropriate antimicrobial therapy. We conducted a monocentric pre/post study comparing the time to result from direct microscopic examination (DE) to bacterial identification (BI) in positive blood cultures between 2 different periods: P1 without BCID2 and P2 with BCID2. Appropriate treatments prescribed before DE and after DE / BCID2 and after BI / BCID2 were compared using direct proportion comparison and survival analysis. For mono-microbial bloodstream infections, the proportion of appropriate antimicrobial treatment after DE was 50% in P1 vs. 87.5% after BCID2 in P2 (P < 0.001) for Gram-negative bacteria and 33.0% in P1 vs. 64.4% in P2 (P < 0.01) for Gram-positive bacteria. A significant difference (P = 0.04) was recorded with survival curves for Gram positive bacteria. BCID2 seems effective in reducing the time for prescribing appropriate antimicrobials.

Predictive Value of Combination of Procalcitonin and Predisposition, Infection, Response, and Organ Dysfunction (PIRO) System in Septic Patients with Positive Blood Cultures in the Emergency Department

Purpose

Procalcitonin and predisposition, infection, response, and organ dysfunction (PIRO) system have high predictive value for the prognosis of critically ill patients. There are few studies on the predictive value of patients with positive blood cultures. The aim of the study was to evaluate risk stratification and sepsis-related mortality in patients with positive blood cultures via procalcitonin (PCT) combined with the PIRO system in emergency departments (ED).

Methods

A total of 1074 patients with positive blood cultures were admitted to Beijing Chao-Yang Hospital ED from December 2017 to October 2020. Their serum PCT was recorded, along with a Sequential Organ Failure Assessment (SOFA) score, Mortality in Emergency Department Sepsis (MEDS) score, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, and PIRO score to predict the prognosis of septic patients with positive blood culture in terms of ICU (intensive care unit) admission, multiple organ dysfunction syndrome (MODS) development, and 28-day mortality. Receiver operating characteristic (ROC) curves and logistic regression analysis were used to assess the prognostic value of the scoring systems.

Results

A total of 978 patients met the inclusion criteria. PCT, MEDS, APACHE II, and PIRO scores were found to independently predict ICU-admission, MODS development, and 28-day mortality (P<0.05), whereas SOFA did not. The AUC values of the PCT, MEDS, APACHE II, and PIRO scores for ICU-admission were 0.620, 0.740, 0.780, and 0.751, respectively. In the prediction of 28-day mortality, the AUC values of PCT, MEDS, APACHE II, and PIRO were 0.782, 0.745, 0.805, and 0.831, respectively. The AUC values combined PCT and PIRO system in predicting MODS and 28-day mortality were better than when predicting ICU-admission.

Conclusion

This study indicates that PCT combined with the PIRO scoring system has a higher predictive value and is superior in predicting MODS and 28-day mortality in septic patients with positive blood cultures.

Emerging Biosensing Technologies towards Early Sepsis Diagnosis and Management

Sepsis is defined as a systemic inflammatory dysfunction strictly associated with infectious diseases, which represents an important health issue whose incidence is continuously increasing worldwide. Nowadays, sepsis is considered as one of the main causes of death that mainly affects critically ill patients in clinical settings, with a higher prevalence in low-income countries. Currently, sepsis management still represents an important challenge, since the use of traditional techniques for the diagnosis does not provide a rapid response, which is crucial for an effective infection management. Biosensing systems represent a valid alternative due to their characteristics such as low cost, portability, low response time, ease of use and suitability for point of care/need applications. This review provides an overview of the infectious agents associated with the development of sepsis and the host biomarkers suitable for diagnosis and prognosis. Special focus is given to the new emerging biosensing technologies using electrochemical and optical transduction techniques for sepsis diagnosis and management.

Treatment outcomes of secondary bacteraemia in patients treated with ceftaroline fosamil: pooled results from six phase III clinical trials

OBJECTIVES

This exploratory pooled analysis assessed the efficacy and safety of ceftaroline fosamil and comparators across six phase III clinical trials in adults with community-acquired pneumonia (CAP) or complicated skin and soft-tissue infection (cSSTI) and secondary bacteraemia.

METHODS

In each trial, FOCUS 1 and 2 (CAP), Asia CAP trial, CANVAS 1 and 2 (cSSTI) and COVERS (cSSTI), patients were randomised to ceftaroline fosamil [600 mg q12h by 1-h i.v. infusion, except in COVERS (600 mg q8h by 2-h i.v. infusion), adjusted for renal function] or comparator. Efficacy assessments included clinical and microbiological responses at test-of-cure visit [microbiological modified intent-to-treat (mMITT) population]. Safety outcomes were assessed.

RESULTS

The pooled mMITT population comprised 1976 patients, of whom 138 had baseline bacteraemia (ceftaroline fosamil, n = 72; comparator, n = 66). Predominant baseline blood pathogens were Staphylococcus aureus (n = 29), Streptococcus pneumoniae (n = 19) and other streptococci (n = 12). Clinical cure rates in bacteraemic patients were 55/72 (76.4%) and 51/66 (77.3%) for ceftaroline fosamil and comparators, respectively, and in non-bacteraemic patients were 822/966 (85.1%) and 717/872 (82.2%). Favourable microbiological response rates in bacteraemic patients were 56/72 (77.8%) for ceftaroline fosamil and 54/66 (81.8%) for comparators, and in non-bacteraemic patients were 825/966 (85.4%) and 719/872 (82.5%). Adverse events in bacteraemic patients were consistent with the known ceftaroline fosamil safety profile or the underlying indications.

CONCLUSION

These pooled clinical and microbiological efficacy data demonstrate generally favourable outcomes for ceftaroline fosamil in patients with CAP or cSSTI and secondary bacteraemia. [Trial Registration: NCT00621504, NCT00509106; NCT01371838; NCT00424190, NCT00423657; NCT01499277].

AIEgens for Bacterial Imaging and Ablation

Accurate and sensitive diagnosis of pathogenic bacterial infection is a fundamental first step for correct bacteria management, helping to avoid the development of drug-resistant bacteria caused by the inappropriate use and overuse of antibiotics. Fluorescence probes as a promising visual tool can help identify pathogens rapidly and reliably. However, rigidly structured traditional fluorescence probes generally suffer from the drawback of aggregation-caused quenching (ACQ) effect, which greatly undermines their advantages with respect to sensitivity. Luminogens with aggregation-induced emission properties, namely AIEgens, can overcome the ACQ effect and certain AIEgen-based materials are capable of generating reactive oxygen species (ROS) in the aggregate states. Hence, they have become powerful tools for imaging and killing bacteria. This review summarizes the recent advances in AIEgens for the diagnosis and treatment of pathogen infections. Special attention has been paid to the molecular design, the application in bacterial imaging and ablation in vitro and in vivo, and the biocompatibility of AIEgens. Finally, the challenges and prospects are discussed in terms of using AIEgens to advance precision therapies for pathogen infections.

Development of a rapid and sensitive analytical system for Pseudomonas aeruginosa based on reverse transcription quantitative PCR targeting of rRNA molecules

For Pseudomonas aeruginosa (PA), infection control and appropriate antimicrobial treatment have become important issues. Diagnosis is critical in managing PA infection, but conventional methods are not highly accurate or rapid. We developed a new PA quantification system based on 23S rRNA-targeted reverse transcription quantitative PCR (RT-qPCR). We confirmed that RT-qPCR can quantify PA directly from clinical samples quickly (within 6 h) and with high sensitivity (blood, 1 cell/mL; stool, 100 cells/g) and without cross-reaction. Also, under antibiotic treatment, PA viable counts detected by this system correlated well with the inflammatory response of infected Caco-2 cells compared to other methods such as culturing and qPCR. Next, we utilized this system on fecal samples collected from 65 septic ICU patients and 44 healthy volunteers to identify ICU infection status. We confirmed that the PA detection ratio in ICU patients was significantly higher than that in healthy volunteers (49.2% vs. 13.6%, P < 0.05). Additionally, we monitored drug-resistant PA in 4 ICU patients by this system. The trends in PA counts accurately reflected various treatment backgrounds such as antibiotic use and mechanical ventilator use. Our results suggest that this RT-qPCR system is beneficial for the early diagnosis and evaluation of appropriate antibacterial treatment and may be a useful tool in combating PA infection.

Mass Spectrometry Proteotyping-Based Detection and Identification of Staphylococcus aureus, Escherichia coli, and Candida albicans in Blood

Bloodstream infections (BSIs), the presence of microorganisms in blood, are potentially serious conditions that can quickly develop into sepsis and life-threatening situations. When assessing proper treatment, rapid diagnosis is the key; besides clinical judgement performed by attending physicians, supporting microbiological tests typically are performed, often requiring microbial isolation and culturing steps, which increases the time required for confirming positive cases of BSI. The additional waiting time forces physicians to prescribe broad-spectrum antibiotics and empirically based treatments, before determining the precise cause of the disease. Thus, alternative and more rapid cultivation-independent methods are needed to improve clinical diagnostics, supporting prompt and accurate treatment and reducing the development of antibiotic resistance. In this study, a culture-independent workflow for pathogen detection and identification in blood samples was developed, using peptide biomarkers and applying bottom-up proteomics analyses, i.e., so-called "proteotyping". To demonstrate the feasibility of detection of blood infectious pathogens, using proteotyping, Escherichia coli and Staphylococcus aureus were included in the study, as the most prominent bacterial causes of bacteremia and sepsis, as well as Candida albicans, one of the most prominent causes of fungemia. Model systems including spiked negative blood samples, as well as positive blood cultures, without further culturing steps, were investigated. Furthermore, an experiment designed to determine the incubation time needed for correct identification of the infectious pathogens in blood cultures was performed. The results for the spiked negative blood samples showed that proteotyping was 100- to 1,000-fold more sensitive, in comparison with the MALDI-TOF MS-based approach. Furthermore, in the analyses of ten positive blood cultures each of E. coli and S. aureus, both the MALDI-TOF MS-based and proteotyping approaches were successful in the identification of E. coli, although only proteotyping could identify S. aureus correctly in all samples. Compared with the MALDI-TOF MS-based approaches, shotgun proteotyping demonstrated higher sensitivity and accuracy, and required significantly shorter incubation time before detection and identification of the correct pathogen could be accomplished.

A label-free impedance biosensing assay based on CRISPR/Cas12a collateral activity for bacterial DNA detection

The rapid and selective identification in the clinical setting of pathogenic bacteria causing healthcare associated infections (HAIs) and in particular blood stream infections (BSIs) is a major challenge, as the number of people affected worldwide and the associated mortality are on the rise. In fact, traditional laboratory techniques such culture and polymerase chain reaction (PCR)-based methodologies are often associated to long turnaround times, which justify the pressing need for the development of rapid, specific and portable point of care devices. The recently discovered clustered regularly interspaced short palindromic repeat loci (CRISPR) and the new class of programmable endonuclease enzymes called CRISPR associated proteins (Cas) have revolutionised molecular diagnostics. The use of Cas proteins in optical and electrochemical biosensing devices has significantly improved the detection of nucleic acids in clinical samples. In this study, a CRISPR/Cas12a system was coupled with electrochemical impedance spectroscopy (EIS) measurements to develop a label-free biosensing assay for the detection of Escherichia coli and Staphylococcus aureus, two bacterial species commonly associated to BSI infections. The programmable Cas12a endonuclease activity, induced by a specific guide RNA (gRNA), and the triggered collateral activity were assessed in in vitro restriction analyses, and evaluated thanks to impedance measurements using a modified gold electrode. The Cas12a/gRNA system was able to specifically recognize amplicons from different clinical isolates of E. coli and S. aureus with a limit of detection of 3 nM and a short turnaround time approximately of 1.5 h. To the best of our knowledge, this is the first biosensing device based on CRISPR/Cas12a label free impedance assay.

Rapid and sensitive detection of Staphylococcus aureus and Klebsiella pneumonia based on bacitracin-modified Fe3O4@PDA magnetic beads combined with matrix-assisted laser desorption ionization-time of flight mass spectrometry

The highly effective detection of pathogens in complex biological samples is an attractive and critical topic of study. Bacitracin is a novel broad-spectrum antimicrobial peptide to enrich bacteria via interactions with the membrane surface of the different bacterial cells. In this study, for the first time, bacitracin was immobilized on the surface of Fe3O4@PDA magnetic nanoparticles for the enrichment of Staphylococcus aureus (G+) and Klebsiella pneumoniae (G-). Combined with matrix-assisted laser desorption ionization time-of-flight mass spectrometry, a rapid and sensitive detection method for these two bacteria was developed. In this method, the detectable concentration of bacteria was decreased by 2-3 orders of magnitude in unenriched samples. The enrichment and identification can be completed in one hour. All these results demonstrated that the bacitracin-functionalized magnetic composite has potential for use in the large-scale enrichment and isolation of target pathogens from complex biological samples, opening a new avenue for the rapid and sensitive detection of pathogens.

Oxford nanopore sequencing in clinical microbiology and infection diagnostics

Extended turnaround times and large economic costs hinder the usage of currently applied screening methods for bacterial pathogen identification (ID) and antimicrobial susceptibility testing. This review provides an overview of current detection methods and their usage in a clinical setting. Issues of timeliness and cost could soon be circumvented, however, with the emergence of detection methods involving single molecule sequencing technology. In the context of bringing diagnostics closer to the point of care, we examine the current state of Oxford Nanopore Technologies (ONT) products and their interaction with third-party software/databases to assess their capabilities for ID and antimicrobial resistance (AMR) prediction. We outline and discuss a potential diagnostic workflow, enumerating (1) rapid sample prep kits, (2) ONT hardware/software and (3) third-party software and databases to improve the cost, accuracy and turnaround times for ID and AMR. Multiple studies across a range of infection types support that the speed and accuracy of ONT sequencing is now such that established ID and AMR prediction tools can be used on its outputs, and so it can be harnessed for near real time, close to the point-of-care diagnostics in common clinical circumstances.

Real-time PCR versus MALDI-TOF MS and culture-based techniques for diagnosis of bloodstream and pyogenic infections in humans and animals

AIMS

This study was applied to evaluate the usefulness of a high-throughput sample preparation protocol prior to the application of quantitative real-time PCR (qPCR) for the early diagnosis of bloodstream and pyogenic infections in humans and animals compared to matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and classical culture.

METHODS AND RESULTS

Saponin-mediated selective host cell lysis combined with DNase-1 was applied for processing of whole blood and pus clinical samples collected from suspected cases of septicaemia and pyogenic infections in humans and animals. The pre-PCR processing strategy enabled the recovery of microbial cells with no changes in their colony forming units immediately after the addition of saponin. DNase-1 was efficient for removing the DNAs from the host cells as well as dead cells with damaged cell membranes. The metagenomic qPCR and MALDI-TOF MS could identify the bacterial community of sepsis at species level with a concordance of 97·37% unlike the conventional culture. According to qPCR results, Staphylococcus aureus (24·24%) was predominated in animal pyogenic infections, whereas Klebsiella pneumonia (31·81%) was commonly detected in neonatal sepsis.

CONCLUSIONS

Saponin combined with DNase-1 allowed the efficient recovery of microbial DNA from blood and pus samples in sepsis using qPCR assay.

SIGNIFICANCE AND IMPACT OF THE STUDY

Metagenomic qPCR could identify a broad range of bacteria directly from blood and pus with more sensitivity, higher discriminatory power and shorter turnaround time than those using MALDI-TOF MS and conventional culture. This might allow a timely administration of a prompt treatment.

Beyond Antibiotics: Photo/Sonodynamic Approaches for Bacterial Theranostics

Rapid evolution and propagation of multidrug resistance among bacterial pathogens are outpacing the development of new antibiotics, but antimicrobial photodynamic therapy (aPDT) provides an excellent alternative. This treatment depends on the interaction between light and photoactivated sensitizer to generate reactive oxygen species (ROS), which are highly cytotoxic to induce apoptosis in virtually all microorganisms without resistance concern. When replacing light with low-frequency ultrasonic wave to activate sensitizer, a novel ultrasound-driven treatment emerges as antimicrobial sonodynamic therapy (aSDT). Recent advances in aPDT and aSDT reveal golden opportunities for the management of multidrug resistant bacterial infections, especially in the theranostic application where imaging diagnosis can be accomplished facilely with the inherent optical characteristics of sensitizers, and the generated ROS by aPDT/SDT cause broad-spectrum oxidative damage for sterilization. In this review, we systemically outline the mechanisms, targets, and current progress of aPDT/SDT for bacterial theranostic application. Furthermore, potential limitations and future perspectives are also highlighted.

Classical Microbiological Diagnostics of Bacteremia: Are the Negative Results Really Negative? What is the Laboratory Result Telling Us About the "Gold Standard"?

Standard blood cultures require at least 24–120 h to be reported as preliminary positive. The objective of this study was to compare the reliability of Gram staining and fluorescent in-situ hybridization (FISH) for detecting bacteria in otherwise negative blood culture bottles. Ninety-six sets were taken from patients with a diagnosis of sepsis. Six incomplete blood culture sets and eight blood cultures sets demonstrating positive growth were excluded. We performed Gram stain and FISH on 82 sets taken from post-operative septic patients: 82 negative aerobic blood cultures, 82 anaerobic blood cultures, and 82 blood samples, as well as 57 blood samples taken from healthy volunteers. From the eighty-two blood sets analyzed from the septic patients, Gram stain visualized bacteria in 62.2% of blood samples, 35.4% of the negative aerobic bottles, and in 31.7% of the negative anaerobic bottles. Utilizing FISH, we detected bacteria in 75.6%, 56.1%, and 64.6% respectively. Among the blood samples from healthy volunteers, FISH detected bacteria in 64.9%, while Gram stain detected bacteria in only 38.6%. The time needed to obtain the study results using Gram stain was 1 h, for FISH 4 h, and for the culture method, considering the duration of growth, 5 days. Gram stain and FISH allow quick detection of bacteria in the blood taken directly from a patient. Finding phagocytosed bacteria, which were also detected among healthy individuals, confirms the hypothesis that blood microbiome exists.

Identification and quantitation of clinically relevant microbes in patient samples: Comparison of three k-mer based classifiers for speed, accuracy, and sensitivity

Infections are a serious health concern worldwide, particularly in vulnerable populations such as the immunocompromised, elderly, and young. Advances in metagenomic sequencing availability, speed, and decreased cost offer the opportunity to supplement or even replace culture-based identification of pathogens with DNA sequence-based diagnostics. Adopting metagenomic analysis for clinical use requires that all aspects of the workflow are optimized and tested, including data analysis and computational time and resources. We tested the accuracy, sensitivity, and resource requirements of three top metagenomic taxonomic classifiers that use fast k-mer based algorithms: Centrifuge, CLARK, and KrakenUniq. Binary mixtures of bacteria showed all three reliably identified organisms down to 1% relative abundance, while only the relative abundance estimates of Centrifuge and CLARK were accurate. All three classifiers identified the organisms present in their default databases from a mock bacterial community of 20 organisms, but only Centrifuge had no false positives. In addition, Centrifuge required far less computational resources and time for analysis. Centrifuge analysis of metagenomes obtained from samples of VAP, infected DFUs, and FN showed Centrifuge identified pathogenic bacteria and one virus that were corroborated by culture or a clinical PCR assay. Importantly, in both diabetic foot ulcer patients, metagenomic sequencing identified pathogens 4-6 weeks before culture. Finally, we show that Centrifuge results were minimally affected by elimination of time-consuming read quality control and host screening steps.

Real World Patterns of Antimicrobial Use and Microbiology Investigations in Patients with Sepsis outside the Critical Care Unit: Secondary Analysis of Three Nation-Wide Point Prevalence Studies

Recent description of the microbiology of sepsis on the wards or information on the real-life antibiotic choices used in sepsis is lacking. There is growing concern of the indiscriminate use of antibiotics and omission of microbiological investigations in the management of septic patients. We performed a secondary analysis of three annual 24-h point-prevalence studies on the general wards across all Welsh acute hospitals in years 2016–2018. Data were collected on patient demographics, as well as radiological, laboratory and microbiological data within 48-h of the study. We screened 19,453 patients over the three 24 h study periods and recruited 1252 patients who fulfilled the entry criteria. 775 (64.9%) patients were treated with intravenous antibiotics. Only in 33.65% (421/1252) of all recruited patients did healthcare providers obtain blood cultures; in 25.64% (321/1252) urine cultures; in 8.63% (108/1252) sputum cultures; in 6.79% (85/1252) wound cultures; in 15.25% (191/1252) other cultures. Out of the recruited patients, 59.1% (740/1252) fulfilled SEPSIS-3 criteria. Patients with SEPSIS-3 criteria were significantly more likely to receive antibiotics than the non-septic cohort (p < 0.0001). In a multivariable regression analysis increase in SOFA score, increased number of SIRS criteria and the use of the official sepsis screening tool were associated with antibiotic administration, however obtaining microbiology cultures was not. Our study shows that antibiotics prescription practice is not accompanied by microbiological investigations. A significant proportion of sepsis patients are still at risk of not receiving appropriate antibiotics treatment and microbiological investigations; this may be improved by a more thorough implementation of sepsis screening tools.

A 'culture' shift: Application of molecular techniques for diagnosing polymicrobial infections

With the advancement of microbiological discovery, it is evident that many infections, particularly bloodstream infections, are polymicrobial in nature. Consequently, new challenges have emerged in identifying the numerous etiologic organisms in an accurate and timely manner using the current diagnostic standard. Various molecular diagnostic methods have been utilized as an effort to provide a fast and reliable identification in lieu or parallel to the conventional culture-based methods. These technologies are mostly based on nucleic acid, proteins, or physical properties of the pathogens with differing advantages and limitations. This review evaluates the different molecular methods and technologies currently available to diagnose polymicrobial infections, which will help determine the most appropriate option for future diagnosis.

Color-coded molecular beacons for multiplex PCR screening assays

The number of different fluorescent colors that can be distinguished in a PCR screening assay restricts the number of different targets that can be detected. If only six colors can be distinguished, and the probe for each target is labeled with a unique color, then only six different targets can be identified. Yet, it is often desirable to identify more targets. For instance, the rapid identification of which bacterial species (if any) is present in a patient's normally sterile blood sample, out of a long list of species, would enable appropriate actions to be taken to prevent sepsis. We realized that the number of different targets that can be identified in a screening assay can be increased significantly by utilizing a unique combination of two colors for the identification of each target species. We prepared a demonstration assay in which 15 different molecular beacon probe pairs were present, each pair specific for the same identifying sequence in the 16S ribosomal RNA gene of a different bacterial species, and each pair labeled with a unique combination of two fluorophores out of the six differently colored fluorophores that our PCR instrument could distinguish. In a set of PCR assays, each containing all 30 color-coded molecular beacons, and each containing DNA from a different bacterial species, the only two colors that arose in each real-time assay identified the species-specific target sequence that was present. Due to the intrinsic low background of molecular beacon probes, these reactions were specific and extremely sensitive, and the threshold cycle reflected the abundance of the target sequence present in each sample.

High nuc DNA load in whole blood is associated with sepsis, mortality and immune dysregulation in Staphylococcus aureus bacteraemia

BACKGROUND

Staphylococcus aureus bacteraemia is a disease with varying presentation, ranging from uncomplicated to life-threatening infections. In S. aureus bacteraemia, a high load of bacterial DNA in blood has been linked to mortality. We hypothesized that a high DNA load would also be linked to the presence of sepsis, and to high C-reactive protein (CRP) and lymphopaenia, indicating inflammation and immunosuppression.

METHODS

Twenty-seven patients with culture-proven S. aureus bacteraemia, 13 (48%) with sepsis and six (22%) non-survivors, were enrolled in a prospective study. Blood samples were collected on days 0, 1-2, 3-4, 6-8, 13-15 and 26-30, and subjected to droplet digital PCR targeting the nuc gene to determine the nuc DNA load.

RESULTS

nuc DNA was detected on days 0-2 in 22 patients (81%), and on days 6-8 in three patients (all non-survivors). The nuc DNA load on days 1-2 was significantly elevated in patients with sepsis (median 2.69 versus 1.32 log10 copies/mL; p = .014) and in non-survivors (median 2.5 versus 1.0 log10 copies/mL; p = .033). Patients with a high nuc DNA load (>3.0 log10 copies/mL) on days 1-2 had significantly elevated CRP levels at all timepoints, and significantly decreased lymphocyte counts on days 0, 1-2, 13-15 and 26-30.

CONCLUSIONS

Our results indicate that a high initial load of S. aureus DNA in blood is associated with sepsis, mortality and persistent immune dysregulation in S. aureus bacteraemia patients. Further studies are needed to define the role of bacterial DNA load monitoring in the management of S. aureus bacteraemia.

Defining System Requirements for Simplified Blood Culture to Enable Widespread Use in Resource-Limited Settings

Bacterial blood stream infections (BSI) are a common cause of mortality and morbidity globally. As the causative agents and the resulting treatment decisions vary, near-patient testing and surveillance tools are necessary to monitor bacterial causes and resistance to antimicrobial agents. The gold standard to identify BSIs is blood culture (BC), a methodology not widely available in resource-limited settings. The aim of the study was to map out a target product profile of a simplified BC system (SBCS) to inform product development efforts. To identify the desired characteristics of a SBCS, we enlisted a small group of specialists working in Africa and Asia. Questions were used to understand challenges and how these constraints inform system requirements. The specialists were infectious disease physicians, public health/clinical microbiologists, clinical researchers, and technology experts with different geographical backgrounds. All suggested that BC should ideally be available at the district hospital level. Many of the same operational challenges, such as limited availability of culture bottles, electricity and internet connectivity, profuse dust, the lack of ambient temperature control, and human capacity constraints were identified across the different regions. BCs, although the accepted gold standard for diagnosis of BSIs, are not widely available outside of reference/research centers in Africa and Asia. To extend the reach of this important tool, it is crucial to engage product developers and academic research partners to develop accessible alternatives.

Identification of pathogenic bacteria in human blood using IgG-modified Fe3O4 magnetic beads as a sorbent and MALDI-TOF MS for profiling

A method is described for fast identification of bacteria by combining (a) the enrichment of bacterial cells by using magnetite (Fe₃O₄) magnetic beads modified with human IgG (IgG@Fe₃O₄) and (b) MALDI-TOF MS analysis. IgG has affinity to protein A, protein G, protein L and glycans on the surface of bacterial cells, and IgG@Fe₃O₄. It therefore is applicable to the preconcentration of a range of bacterial species. The feasibility of the method has been demonstrated by collecting six species of pathogenic bacteria (Gram-positives: Staphylococcus aureus and Kocuria rosea; Gram-negatives: Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae and Pseudomonas aeruginosa). Bacteria with concentrations as low as 10 CFU·mL^-1 in spiked water samples were extracted by this sorbent with recovery rates of >50%. After enrichment, bacteria on the IgG@Fe₃O₄ sorbent were further identified by MALDI-TOF MS. Bacteria in concentrations as low as 10⁵ CFU in 100 μL of human whole blood can be identified by the method. Compared to other blood culture based tests, the culture time is shortened by 40% (from ~10 h to ~6 h), and the plate culture procedure (overnight) is avoided. After short blood culture, the enrichment and identification can be finished in one hour. The IgG@Fe₃O₄ is of practical value in clinical diagnosis and may be combined with other identification methods, e.g. PCR, Raman spectroscopy, infrared spectroscopy, etc. Graphical abstract A non-targeted, fast and sensitive assay for bacterial identification from human blood has been developed based on the enrichment of bacteria by IgG@Fe₃O₄ and identification by MALDI-TOF MS.

Diagnosis of bloodstream infections from positive blood cultures and directly from blood samples: recent developments in molecular approaches

BACKGROUND

Bloodstream infections are a major cause of death with increasing incidence and severity. Blood cultures are still the reference standard for microbiological diagnosis, but are rather slow. Molecular methods can be used as add-on complementary assays. They can be useful to speed up microbial identification and to predict antimicrobial susceptibility, applied to direct blood samples or positive blood cultures.

AIM

To review recent developments in molecular-based diagnostic platforms used for the identification of bloodstream infections, with a focus on assays performed directly on blood samples and positive blood cultures.

SOURCES

Peer reviewed articles, conference abstracts, and manufacturers' websites.

CONTENT

We give an update on recent developments of molecular methods in diagnosing BSIs. We first describe the currently available molecular methods to be used for positive blood cultures including: a) in situ hybridization-based methods; b) DNA-microarray-based hybridization technology; c) nucleic acid amplification-based methods; and d) combined methods. Subsequently, molecular methods applied directly to whole blood samples are discussed, including the use of nucleic acid amplification-based methods, T2 magnetic resonance-based methods, and metagenomics for diagnosing BSIs.

IMPLICATIONS

Advances in molecular-based methods complementary to conventional blood culture diagnostics and antimicrobial stewardship programmes may optimize infection management by allowing rapid identification of pathogens and relevant antimicrobial resistance genes. Rapid diagnosis of the causing microorganism and relevant resistance determinants is important for early administration and modification of appropriate antimicrobial therapy. Ultimately, this may lead to improved quality and cost-effectiveness of health care, as well as reduced antimicrobial resistance selection.

Evaluation of the Clinical Utility of a Real-time PCR Assay for the Diagnosis of Streptococcus pneumoniae Bacteremia in Children: A Retrospective Diagnostic Accuracy Study

BACKGROUND

The widespread uptake of pneumococcal vaccines has substantially reduced the incidence of invasive pneumococcal disease, such that pneumococcal bacteremia in children is now considered a relatively rare event. The objective of this study was to ascertain the clinical utility of a Streptococcus pneumoniae real-time polymerase chain reaction (PCR) assay compared with standard blood culture for the diagnosis of pneumococcal bacteremia in children in the post-vaccine era.

METHODS

A systematic retrospective review of laboratory and patient records from Children's University Hospital, Temple Street, during a 6-year period was performed. Paired blood PCR and blood culture specimens from children younger than 16 years of age were investigated. Statistical analysis was performed to measure the diagnostic accuracy of PCR versus routine bacterial culture techniques.

RESULTS

More than 1900 PCR test requests were examined from 2010 to 2015, of which 1561 paired PCR and blood culture specimens met criteria for inclusion in the statistical analysis. The PCR assay demonstrated high specificity (99%, confidence interval 95%: 98.81%-99.69%); however, the sensitivity was low compared with that of blood culture (47%, confidence interval 95%: 21.27%-73.41%). Investigation of 10 PCR-positive/culture-negative cases revealed that these cases ranged from definite, probable, and possible significance, indicating a low false positivity rate associated with the assay.

CONCLUSION

This study demonstrates the limited utility of blood PCR testing for S. pneumoniae in pediatric patients without radiographic evidence pneumonia or empyema. Moreover, we report that PCR may be a useful diagnostic tool when blood cultures are negative because of antimicrobial therapy before sampling. Given that the incidence of pneumococcal disease has decreased considerably in recent years, justification of S. pneumoniae PCR requisition is necessary. Hence, new guidelines for pediatric pneumococcal blood PCR testing have been introduced at the Irish Meningitis and Sepsis Reference Laboratory.

DNA extraction from primary liquid blood cultures for bloodstream infection diagnosis using whole genome sequencing

PURPOSE

Speed of bloodstream infection diagnosis is vital to reduce morbidity and mortality. Whole genome sequencing (WGS) performed directly from liquid blood culture could provide single-assay species and antibiotic susceptibility prediction; however, high inhibitor and human cell/DNA concentrations limit pathogen recovery. We develop a method for the preparation of bacterial DNA for WGS-based diagnostics direct from liquid blood culture.

METHODOLOGY

We evaluate three commercial DNA extraction kits: BiOstic Bacteraemia, Amplex Hyplex and MolYsis Plus. Differential centrifugation, filtration, selective lysis and solid-phase reversible immobilization bead clean-up are tested to improve human cells/DNA and inhibitor removal. Using WGS (Illumina/MinION), we assess human DNA removal, pathogen recovery, and predict species and antibiotic susceptibility inpositive blood cultures of 44 Gram-negative and 54 Staphylococcus species.Results/Key findings. BiOstic kit extractions yield the greatest mean DNA concentration, 94-301 ng µl^-1, versus 0-2.5 ng µl^-1 using Amplex and MolYsis kits. However, we note higher levels of inhibition (260/280 ratio 0.9-2.1) and human DNA (0.0-4.4×10⁶ copies) in BiOstic extracts. Differential centrifugation (2000 g, 1 min) prior to BiOstic extraction reduces human DNA by 63-89 % with selective lysis minimizing by a further 62 %. Post-extraction bead clean-up lowers inhibition. Overall, 67 % of sequenced samples (Illumina MiSeq) contain <10 % human DNA, with >93 % concordance between WGS-based species and susceptibility predictions and clinical diagnosis. If >60 % of sequencing reads are human (7/98 samples) susceptibility prediction becomes compromised. Novel MinION-based WGS (n=9) currently gives rapid species identification but not susceptibility prediction.

CONCLUSION

Our method for DNA preparation allows WGS-based diagnosis direct from blood culture bottles, providing species and antibiotic susceptibility prediction in a single assay.

Identification by mass spectrometry and automated susceptibility testing from positive bottles: a simple, rapid, and standardized approach to reduce the turnaround time in the management of blood cultures

BACKGROUND

Speeding up identification and antimicrobial susceptibility testing (AST) is of foremost importance in the management of blood cultures. Here, we describe a simple, rapid, and standardized approach based on a very short-term incubation on solid medium from positive blood cultures followed by MALDI-TOF mass spectrometry identification and automated AST. The aim of the study was to evaluate the impact in the laboratory practice of this new procedure with respect to that previously used (standard method) by comparing TAT and cumulative percentage of final reports to clinicians.

RESULTS

Compared with the standard method, the new procedure gave correct organism identification at genus or species level in 98.4% of monomicrobial samples. AST resulted in 97.7% essential agreement and 98.1% categorical agreement, with 0.9% minor errors, 1.0% major error, and 1.5% very major errors. The mean turnaround time to identification and AST was 61.4 h by using the new method compared to 83.1 h by using standard procedure. Concerning cumulative percentages of final reports, approximately a third of results were available at 48 h from the check-in of the sample when using the new procedure, whereas no final reports were ready at the same time with the standard method.

CONCLUSIONS

The new procedure allows faster and reliable results using a simple and standardized approach. Thus, it represents an important tool for a more rapid management of blood cultures when molecular methods are not available in the laboratory.

Identification of microorganisms grown in blood culture flasks using liquid chromatography–tandem mass spectrometry

Aim: Bloodstream infections are a common cause of disease and a fast and accurate identification of the causative agent or agents of bloodstream infections would aid the start of adequate treatment. Materials & methods: A liquid chromatography–tandem mass spectrometry (LC–MS/MS) shotgun proteomics method was developed for the identification of bacterial species directly from blood cultures that were simulated by inoculating blood culture bottles with single or multiple clinically relevant microorganisms. Results: Using LC–MS/MS, the single species were correctly identified in 100% of the blood cultures, whereas for polymicrobial infections, 78% of both species were correctly identified in blood cultures. Conclusion: The LC–MS/MS method allows for the identification of the causative agent of positive blood cultures.

Rapid diagnosis of sepsis with TaqMan-Based multiplex real-time PCR

BACKGROUND

The survival rate of septic patients mainly depends on a rapid and reliable diagnosis. A rapid, broad range, specific and sensitive quantitative diagnostic test is the urgent need. Thus, we developed a TaqMan-Based Multiplex real-time PCR assays to identify bloodstream pathogens within a few hours.

METHODS

Primers and TaqMan probes were designed to be complementary to conserved regions in the 16S rDNA gene of different kinds of bacteria. To evaluate accurately, sensitively, and specifically, the known bacteria samples (Standard strains, whole blood samples) are determined by TaqMan-Based Multiplex real-time PCR. In addition, 30 blood samples taken from patients with clinical symptoms of sepsis were tested by TaqMan-Based Multiplex real-time PCR and blood culture.

RESULTS

The mean frequency of positive for Multiplex real-time PCR was 96% at a concentration of 100 CFU/mL, and it was 100% at a concentration greater than 1000 CFU/mL. All the known blood samples and Standard strains were detected positively by TaqMan-Based Multiplex PCR, no PCR products were detected when DNAs from other bacterium were used in the multiplex assay. Among the 30 patients with clinical symptoms of sepsis, 18 patients were confirmed positive by Multiplex real-time PCR and seven patients were confirmed positive by blood culture.

CONCLUSION

TaqMan-Based Multiplex real-time PCR assay with highly sensitivity, specificity and broad detection range, is a rapid and accurate method in the detection of bacterial pathogens of sepsis and should have a promising usage in the diagnosis of sepsis.

Sepsis and septic shock: Pathogenesis and treatment perspectives

The majority of bacteremias do not develop to sepsis: bacteria are cleared from the bloodstream. Oxygen released from erythrocytes and humoral immunity kill bacteria in the bloodstream. Sepsis develops if bacteria are resistant to oxidation and proliferate in erythrocytes. Bacteria provoke oxygen release from erythrocytes to arterial blood. Abundant release of oxygen to the plasma triggers a cascade of events that cause: 1. oxygen delivery failure to cells; 2. oxidation of plasma components that impairs humoral regulation and inactivates immune complexes; 3. disseminated intravascular coagulation and multiple organs' failure. Bacterial reservoir inside erythrocytes provides the long-term survival of bacteria and is the cause of ineffectiveness of antibiotics and host immune reactions. Treatment perspectives that include different aspects of sepsis development are discussed.

Rapid Detection of Urinary Tract Infections via Bacterial Nuclease Activity

Rapid and accurate bacterial detection methods are needed for clinical diagnostic, water, and food testing applications. The wide diversity of bacterial nucleases provides a rich source of enzymes that could be exploited as signal amplifying biomarkers to enable rapid, selective detection of bacterial species. With the exception of the use of micrococcal nuclease activity to detect Staphylococcus aureus, rapid methods that detect bacterial pathogens via their nuclease activities have not been developed. Here, we identify endonuclease I as a robust biomarker for E. coli and develop a rapid ultrasensitive assay that detects its activity. Comparison of nuclease activities of wild-type and nuclease-knockout E. coli clones revealed that endonuclease I is the predominant DNase in E. coli lysates. Endonuclease I is detectable by immunoblot and activity assays in uropathogenic E. coli strains. A rapid assay that detects endonuclease I activity in patient urine with an oligonucleotide probe exhibited substantially higher sensitivity for urinary tract infections than that reported for rapid urinalysis methods. The 3 hr turnaround time is much shorter than that of culture-based methods, thereby providing a means for expedited administration of appropriate antimicrobial therapy. We suggest this approach could address various unmet needs for rapid detection of E. coli.

Early Identification and Treatment of Pathogens in Sepsis: Molecular Diagnostics and Antibiotic Choice

Sepsis and septic shock are serious conditions associated with high morbidity and mortality. Rapid molecular methods for detection of microorganisms and antimicrobial resistance genes from positive blood cultures or whole blood have evolved over the past 10 years. Such diagnostic methods coupled with therapeutic interventional programs are desirable to improve the overall clinical outcome and mortality. This article discusses the usefulness of current molecular test methods for the diagnosis of sepsis and their potential to enhance the success of antimicrobial stewardship programs. Clinicians and laboratories alike must appreciate key factors influencing the appropriate use and potential impact of these methods.

Individualized antibiotic strategies

PURPOSE OF REVIEW

Infections are common complications in critically ill patients and are frequently treated with antibiotics. Unfortunately, delivery of optimal therapy is complicated because efficacy of antimicrobials is influenced by the timing of treatment initiation, the use of combination therapy, and the optimization of drug dosing.

RECENT FINDINGS

Early diagnosis of infection is mandatory to provide a rapid and appropriate antibiotic therapy. The presence of less susceptible strains, in particular for hospital-acquired infections, or patients with severe disease, such as the presence of septic shock, may need combination antibiotic therapy. Antibiotic pharmacokinetics, notably volume of distribution and total body clearance, are significantly altered in these critically ill patients and can influence the attainment of adequate circulating levels when standard dosage regimens are administered. Higher dosing should be considered in such patients, although in case of renal impairment and reduced clearance, drug accumulation could also result in some side-effects. Nebulized antibiotics may provide a better clinical response than systemic antibiotics in ventilator-associated pneumonia because of multidrug-resistant pathogens.

SUMMARY

The optimal use of antibiotics in the management of severe infections is an important challenge for ICU physicians. Antimicrobial therapy needs to be individualized according to specific patient characteristics, infecting organisms, and susceptibility patterns.

A novel method for the rapid detection of microbes in blood using pleurocidin antimicrobial peptide functionalized piezoelectric sensor

The rapid detection of microbes is critical in clinical diagnosis and food safety. Culture-dependent assays are the most widely used microbial detection methods, but these assays are time-consuming. In this study, a rapid microbial detection method was proposed using a pleurocidin/single-walled carbon nanotubes/interdigital electrode-multichannel series piezoelectric quartz crystal (pleurocidin/SWCNT/IDE-MSPQC) sensor. The selected pleurocidin antimicrobial peptide served as a recognition probe that exhibits broad-spectrum antimicrobial activity and the SWCNT acted as the electronic transducer and cross-linker for the immobilization of pleurocidin on the IDE. The response mechanism of the sensor was based on the specific interaction between pleurocidin and the microbe causing pleurocidin to detach from the SWCNT modified IDE, resulting in a sensitive frequency shift response of the MSPQC. Microbes that may be clinically present in the bloodstream during an infection were successfully detected by the proposed method within 15min. The developed strategy provides a new universal platform for the rapid detection of microbes.

Clinical Significance of Molecular Diagnostic Tools for Bacterial Bloodstream Infections: A Systematic Review

Bacterial bloodstream infection (bBSI) represents any form of invasiveness of the blood circulatory system caused by bacteria and can lead to death among critically ill patients. Thus, there is a need for rapid and accurate diagnosis and treatment of patients with septicemia. So far, different molecular diagnostic tools have been developed. The majority of these tools focus on amplification based techniques such as polymerase chain reaction (PCR) which allows the detection of nucleic acids (both DNA and small RNAs) that are specific to bacterial species and sequencing or nucleic acid hybridization that allows the detection of bacteria in order to reduce delay of appropriate antibiotic therapy. However, there is still a need to improve sensitivity of most molecular techniques to enhance their accuracy and allow exact and on time antibiotic therapy treatment. In this regard, we conducted a systematic review of the existing studies conducted in molecular diagnosis of bBSIs, with the main aim of reporting on clinical significance and benefits of molecular diagnosis to patients. We searched both Google Scholar and PubMed. In total, eighteen reviewed papers indicate that shift from conventional diagnostic methods to molecular tools is needed and would lead to accurate diagnosis and treatment of bBSI.

Comprehensive detection and identification of bacterial DNA in the blood of patients with sepsis and healthy volunteers using next-generation sequencing method - the observation of DNAemia

Blood is considered to be a sterile microenvironment, in which bacteria appear only periodically. Previously used methods allowed only for the detection of either viable bacteria with low sensitivity or selected species of bacteria. The Next-Generation Sequencing method (NGS) enables the identification of all bacteria in the sample with their taxonomic classification. We used NGS for the analysis of blood samples from healthy volunteers (n = 23) and patients with sepsis (n = 62) to check whether any bacterial DNA exists in the blood of healthy people and to identify bacterial taxonomic profile in the blood of septic patients. The presence of bacterial DNA was found both in septic and healthy subjects; however, bacterial diversity was significantly different (P = 0.002) between the studied groups. Among healthy volunteers, a significant predominance of anaerobic bacteria (76.2 %), of which most were bacteria of the order Bifidobacteriales (73.0 %), was observed. In sepsis, the majority of detected taxa belonged to aerobic or microaerophilic microorganisms (75.1 %). The most striking difference was seen in the case of Actinobacteria phyla, the abundance of which was decreased in sepsis (P < 0.001) and Proteobacteria phyla which was decreased in the healthy volunteers (P < 0.001). Our research shows that bacterial DNA can be detected in the blood of healthy people and that its taxonomic composition is different from the one seen in septic patients. Detection of bacterial DNA in the blood of healthy people may suggest that bacteria continuously translocate into the blood, but not always cause sepsis; this observation can be called DNAemia.

Duplex DNA-Invading γ-Modified Peptide Nucleic Acids Enable Rapid Identification of Bloodstream Infections in Whole Blood

Bloodstream infections are a leading cause of morbidity and mortality. Early and targeted antimicrobial intervention is lifesaving, yet current diagnostic approaches fail to provide actionable information within a clinically viable time frame due to their reliance on blood culturing. Here, we present a novel pathogen identification (PID) platform that features the use of duplex DNA-invading γ-modified peptide nucleic acids (γPNAs) for the rapid identification of bacterial and fungal pathogens directly from blood, without culturing. The PID platform provides species-level information in under 2.5 hours while reaching single-CFU-per-milliliter sensitivity across the entire 21-pathogen panel. The clinical utility of the PID platform was demonstrated through assessment of 61 clinical specimens, which showed >95% sensitivity and >90% overall correlation to blood culture findings. This rapid γPNA-based platform promises to improve patient care by enabling the administration of a targeted first-line antimicrobial intervention.

Bloodstream infections continue to be a major cause of death for hospitalized patients, despite significant improvements in both the availability of treatment options as well their application. Since early and targeted antimicrobial intervention is one of the prime determinants of patient outcome, the rapid identification of the pathogen can be lifesaving. Unfortunately, current diagnostic approaches for identifying these infections all rely on time-consuming blood culture, which precludes immediate intervention with a targeted antimicrobial. To address this, we have developed and characterized a new and comprehensive methodology, from patient specimen to result, for the rapid identification of both bacterial and fungal pathogens without the need for culturing. We anticipate broad interest in our work, given the novelty of our technical approach combined with an immense unmet need.

Genotyping bacterial and fungal pathogens using sequence variation in the gene for the CCA-adding enzyme

BACKGROUND

To allow an immediate treatment of an infection with suitable antibiotics and bactericides or fungicides, there is an urgent need for fast and precise identification of the causative human pathogens. Methods based on DNA sequence comparison like 16S rRNA analysis have become standard tools for pathogen verification. However, the distinction of closely related organisms remains a challenging task. To overcome such limitations, we identified a new genomic target sequence located in the single copy gene for tRNA nucleotidyltransferase fulfilling the requirements for a ubiquitous, yet highly specific DNA marker. In the present study, we demonstrate that this sequence marker has a higher discriminating potential than commonly used genotyping markers in pro- as well as eukaryotes, underscoring its applicability as an excellent diagnostic tool in infectology.

RESULTS

Based on phylogenetic analyses, a region within the gene for tRNA nucleotidyltransferase (CCA-adding enzyme) was identified as highly heterogeneous. As prominent examples for pro- and eukaryotic pathogens, several Vibrio and Aspergillus species were used for genotyping and identification in a multiplex PCR approach followed by gel electrophoresis and fluorescence-based product detection. Compared to rRNA analysis, the selected gene region of the tRNA nucleotidyltransferase revealed a seven to 30-fold higher distinction potential between closely related Vibrio or Aspergillus species, respectively. The obtained data exhibit a superb genome specificity in the diagnostic analysis. Even in the presence of a 1,000-fold excess of human genomic DNA, no unspecific amplicons were produced.

CONCLUSIONS

These results indicate that a relatively short segment of the coding region for tRNA nucleotidyltransferase has a higher discriminatory potential than most established diagnostic DNA markers. Besides identifying microbial pathogens in infections, further possible applications of this new marker are food hygiene controls or metagenome analyses.

Antibiotic treatment algorithm development based on a microarray nucleic acid assay for rapid bacterial identification and resistance determination from positive blood cultures

Rapid diagnosis of bloodstream infections remains a challenge for the early targeting of an antibiotic therapy in sepsis patients. In recent studies, the reliability of the Nanosphere Verigene Gram-positive and Gram-negative blood culture (BC-GP and BC-GN) assays for the rapid identification of bacteria and resistance genes directly from positive BCs has been demonstrated. In this work, we have developed a model to define treatment recommendations by combining Verigene test results with knowledge on local antibiotic resistance patterns of bacterial pathogens. The data of 275 positive BCs were analyzed. Two hundred sixty-three isolates (95.6%) were included in the Verigene assay panels, and 257 isolates (93.5%) were correctly identified. The agreement of the detection of resistance genes with subsequent phenotypic susceptibility testing was 100%. The hospital antibiogram was used to develop a treatment algorithm on the basis of Verigene results that may contribute to a faster patient management.

Real-time polymerase chain reaction and culture in the diagnosis of invasive group B streptococcal disease in infants: a retrospective study

Group B streptococcus (GBS) is a leading cause of invasive disease in infants. Accurate and rapid diagnosis is crucial to reduce morbidity and mortality. Real-time polymerase chain reaction (PCR) targeting the dltR gene was utilised for the direct detection of GBS DNA in blood and cerebrospinal fluid (CSF) from infants at an Irish maternity hospital. A retrospective review of laboratory and patient records during the period 2011-2013 was performed in order to evaluate PCR and culture for the diagnosis of invasive GBS disease. A total of 3570 blood and 189 CSF samples from 3510 infants had corresponding culture and PCR results. Culture and PCR exhibited concordance in 3526 GBS-negative samples and 13 (25%) GBS-positive samples (n = 53). Six (11%) and 34 (64%) GBS-positive samples were positive only in culture or PCR, respectively. Culture and PCR identified more GBS-positive infants (n = 47) than PCR (n = 43) or culture (n = 16) alone. Using culture as the reference standard, the sensitivity, specificity, and positive and negative predictive values for PCR on blood samples were 71.4%, 99.2%, 25% and 99.9%, and for CSF samples, they were 60%, 97.8%, 42.9% and 98.9%, respectively. The sensitivity and positive predictive values were improved (blood: 84.6% and 55%; CSF: 77.8% and 100%, respectively) when maternal risk factors and other laboratory test results were considered. The findings in this study recommend the use of direct GBS real-time PCR for the diagnosis of GBS infection in infants with a clinical suspicion of invasive disease and as a complement to culture, but should be interpreted in the light of other laboratory and clinical findings.

Individuality, phenotypic differentiation, dormancy and 'persistence' in culturable bacterial systems: commonalities shared by environmental, laboratory, and clinical microbiology

For bacteria, replication mainly involves growth by binary fission. However, in a very great many natural environments there are examples of phenotypically dormant, non-growing cells that do not replicate immediately and that are phenotypically 'nonculturable' on media that normally admit their growth. They thereby evade detection by conventional culture-based methods. Such dormant cells may also be observed in laboratory cultures and in clinical microbiology. They are usually more tolerant to stresses such as antibiotics, and in clinical microbiology they are typically referred to as 'persisters'. Bacterial cultures necessarily share a great deal of relatedness, and inclusive fitness theory implies that there are conceptual evolutionary advantages in trading a variation in growth rate against its mean, equivalent to hedging one's bets. There is much evidence that bacteria exploit this strategy widely. We here bring together data that show the commonality of these phenomena across environmental, laboratory and clinical microbiology. Considerable evidence, using methods similar to those common in environmental microbiology, now suggests that many supposedly non-communicable, chronic and inflammatory diseases are exacerbated (if not indeed largely caused) by the presence of dormant or persistent bacteria (the ability of whose components to cause inflammation is well known). This dormancy (and resuscitation therefrom) often reflects the extent of the availability of free iron. Together, these phenomena can provide a ready explanation for the continuing inflammation common to such chronic diseases and its correlation with iron dysregulation. This implies that measures designed to assess and to inhibit or remove such organisms (or their access to iron) might be of much therapeutic benefit.