Multicenter Clinical Evaluation of BacT/Alert Virtuo Blood Culture System

Blood culture time to positivity in pediatric patients with bloodstream infection in rural Gambia

Objectives

There is a lack of data on the time to blood culture positivity (TTP) in pediatric populations in low-income countries. We aimed to assess the host and pathogen factors associated with TTP in children aged under 5 years in rural Gambia.

Methods

Between September 2019 and December 2023, we collected blood cultures from children under 5 years with suspected bloodstream infections. We determined the TTP from the time of culture incubation to when bacterial growth was first detected.

Results

Overall, 547 invasive bacteria pathogens were evaluated. The median TTP was 19.2 hours and 70%, 76%, 89%, and 96% of cases had TTP at 24, 36, 48, and 72 hours, respectively. Streptococcus pneumoniae had the shortest median TTP (17.4 hours), whereas Neisseria species had the longest (45 hours). TTP was dependent on the pathogen and independent of age, sex, temperature, clinical outcome, nutritional status, and length of hospital stay. Gram-positive bacteria had shorter TTP than gram-negative bacteria (18.6 vs 19.6 hours, P < 0.01).

Conclusions

In rural Gambia, most blood cultures from pediatric patients would turn positive within 48 hours of incubation. A maximum of 48 hours of observation after the commencement of antibiotic therapy in hospitalized children may be sufficient for clinicians to receive feedback on blood culture results.

Another way? An investigation into an institution's use of the Wayson stain in re-evaluating "no organisms seen" on Gram stain smears from positive blood cultures

Automated continuous monitoring blood culture instruments identify metabolism byproducts and flag blood culture bottles as "positive." A Gram stain is used to visualize and characterize the microbial growth in the broth and initiate additional testing. When no organisms are seen (NOS) on Gram stain, in our laboratory, bottles are reevaluated with a Wayson stain, a rapid one-step stain that provides contrast between organisms and the background, especially in Gram-negative organisms. In this study, we assess the performance of the Wayson stain on reevaluation of Gram stain NOS blood culture bottles. The study period, August 2022 to July 2023, includes blood cultures that were flagged as positive by the automated blood culture instrument (BACTEC) with accompanying Gram and Wayson stain interpretations and organism identification. 133,463 blood cultures were performed during the study period, and 20,129 cultures were flagged as positive by BACTEC. 601 NOS Gram stain cultures were identified of which 76 had a positive Wayson. The Wayson stain procedure increased the sensitivity of direct organism visualization from 99.32% to 99.71% by identifying 55% (76 of 137) of NOS Gram stain blood culture bottles. Of blood cultures that were positive by BACTEC with NOS Gram and Wayson stains (475), 414 were finalized as no growth and 61 had an isolate (false negatives) of which 49% (30) were yeasts. The Wayson stain aided in detecting gram-negative genera such as Capnocytophaga, Campylobacter, and Fusobacterium species and other rarely identified species.IMPORTANCEThe Wayson stain, a rapid one-step stain that provides contrast between microorganisms and the background, was historically used for the presumptive diagnosis of Yersinia pestis from bubo specimen. In our laboratory, the Wayson stain has long been used to reevaluate blood culture Gram-stained smears from bottles that were flagged as positive by the automated continuous monitoring instrument but where no organisms are seen. In this study, we show that the Wayson stain provides an easily implemented and interpreted technique, other than a repeat Gram stain or acridine orange, to increase the sensitivity of direct organism visualization from blood culture bottles, particularly for Gram-negative organisms.

Metagenomic next-generation sequencing as a diagnostic tool in the clinical routine of an infectious diseases department: a retrospective cohort study

BACKGROUND

Metagenomic next-generation sequencing (mNGS) of circulating cell-free DNA from plasma is a hypothesis-independent broadband diagnostic method for identification of potential pathogens. So far, it has only been investigated in special risk populations (e.g. patients with neutropenic fever).

PURPOSE

To investigate the extent to which mNGS (DISQVER® platform) can be used in routine clinical practice.

METHODS

We collected whole blood specimens for mNGS testing, blood cultures (BC), and pathogen-specific PCR diagnostics. Clinical data and pathogen diagnostics were retrospectively reviewed by an infectious disease expert panel regarding the adjustment of anti-infective therapy.

RESULTS

In 55 selected patients (median age 53 years, 67% male) with heterogeneous diagnoses, a total of 66 different microorganisms and viruses were detected using mNGS (51% viruses, 38% bacteria, 8% fungi, 3% parasites). The overall positivity rate of mNGS was 53% (29/55). Fifty-two out of 66 (79%) potential pathogens detected by mNGS were found in patients with primary or secondary immunodeficiency. The concordance rates of BC and pathogen-specific PCR diagnostics with mNGS testing were 14% (4/28) and 36% (10/28), respectively (p < 0.001). An additional bacterial pathogen (Streptococcus agalactiae) could only be detected by BC. Therapeutic consequences regarding anti-infective therapy were drawn from 23 pathogens (35% of detections), with 18 of these detections occurring in patients with immunodeficiency.

CONCLUSIONS

We conclude that mNGS is a useful diagnostic tool, but should only be performed selectively in addition to routine diagnostics of infectious diseases. The limited number of patients and the retrospective study design do not allow any further conclusions.

Epidemiological Study of Pathogens in Spontaneous Bacterial Peritonitis in 2017-2024-A Preliminary Report of the University Hospital in South-Eastern Poland

Spontaneous Bacterial Peritonitis (SBP) is a serious complication and a common cause of death in patients with liver cirrhosis. Between January 2017 and March 2024, a retrospective study was conducted involving 302 patients (>18 years old) with ascites treated at a tertiary referral center in south-eastern Poland. Microbiological analysis of the ascitic fluids was performed in all patients. The presence of microorganisms was found in samples from 17 patients, and 21 pathogens were isolated, including 15 Gram-positive bacteria and 6 Gram-negative bacteria. Staphylococcus epidermidis, MRCNS (methicillin-resistant coagulase-negative staphylococci, resistant to all beta-lactam antibiotics: penicillins, penicillins with beta-lactamase inhibitor, cephalosporins and carbapenems) was the main pathogen detected (19.05%, 4/21), followed by Enterococcus faecalis (9.52%, 2/21), Enterococcus faecium (9.52%, 2/21), Staphylococcus haemolyticus, MRCNS (4.76%, 1/21), Streptococcus mitis (9.52%, 2/21), Streptococcus parasanguinis (9.52%, 2/21), Micrococcus luteus (4.76%, 1/21) and Bacillus spp. (4.76%, 1/21). The following Gram-negative bacteria were also found in the specimens examined: Escherichia coli, ESBL (extended-spectrum β-lactamase producing E. coli) (4.76%, 1/21), Escherichia coli (4.76%, 1/21), Pseudomonas aeruginosa (4.76%, 1/21), Klebsiella oxytoca (9.52%, 2/21) and Sphingomonas paucimobilis (4.76%, 1/21). Gram-positive bacteria caused nosocomial infections in nine patients with SBP, Gram-negative bacteria caused nosocomial infections in two patients. In six patients with SBP, community-acquired infections caused by Gram-negative bacteria were found in three cases, Gram-positive bacteria in two cases, and in one case, community-acquired infection was caused by mixed Gram-positive and Gram-negative. Bacteria isolated from patients with hospital-acquired SBP showed higher drug resistance than those found in patients with non-hospital SBP. Bacterial infections in cirrhotic patients with complications may be responsible for their deteriorating health. Prompt intervention is critical to reducing mortality.

Machine learning of cell population data, complete blood count, and differential count parameters for early prediction of bacteremia among adult patients with suspected bacterial infections and blood culture sampling in emergency departments

BACKGROUND

Bacteremia is a life-threatening complication of infectious diseases. Bacteremia can be predicted using machine learning (ML) models, but these models have not utilized cell population data (CPD).

METHODS

The derivation cohort from emergency department (ED) of China Medical University Hospital (CMUH) was used to develop the model and was prospectively validated in the same hospital. External validation was performed using cohorts from ED of Wei-Gong Memorial Hospital (WMH) and Tainan Municipal An-Nan Hospital (ANH). Adult patients who underwent complete blood count (CBC), differential count (DC), and blood culture tests were enrolled in the present study. The ML model was developed using CBC, DC, and CPD to predict bacteremia from positive blood cultures obtained within 4 h before or after the acquisition of CBC/DC blood samples.

RESULTS

This study included 20,636 patients from CMUH, 664 from WMH, and 1622 patients from ANH. Another 3143 patients were included in the prospective validation cohort of CMUH. The CatBoost model achieved an area under the receiver operating characteristic curve of 0.844 in the derivation cross-validation, 0.812 in the prospective validation, 0.844 in the WMH external validation, and 0.847 in the ANH external validation. The most valuable predictors of bacteremia in the CatBoost model were the mean conductivity of lymphocytes, nucleated red blood cell count, mean conductivity of monocytes, and neutrophil-to-lymphocyte ratio.

CONCLUSIONS

ML model that incorporated CBC, DC, and CPD showed excellent performance in predicting bacteremia among adult patients with suspected bacterial infections and blood culture sampling in emergency departments.

Subculturing and Gram staining of blood cultures flagged negative by the BACTEC™ FX system: Optimizing the workflow for detection of Cryptococcus neoformans in clinical specimens

Objective

To investigate whether an incubation time of 5 days (Aerobic/F, Anaerobic/F) and 14 days (Myco/F) blood culture bottles is sufficient to prevent false-negative results.

Methods

We evaluated 1,244 blood bottles (344 patients) defined as negative by the BACTEC™ FX system. We also reviewed published cases and our own cases of bloodstream infection caused by Cryptococcus neoformans and simulated different scenarios, including different inoculation concentrations, bottle types, and clinical isolates.

Results

Two bottles (0.16%) were found to contain C. neoformans when subcultured and Gram stained. A 5-day protocol with Aerobic/F bottles was insufficient for the growth of C. neoformans in some cases, and C. neoformans grew better in Myco/F bottles than in Aerobic/F bottles.

Conclusion

Subculturing and Gram staining after a 5-day protocol were important for the detection of C. neoformans, and Myco/F bottles should be collected for the blood culture of C. neoformans.

Impact of Implementation of BacT/Alert Virtuo on Blood Culture Time to Positivity in Sepsis Patients

Time to positivity (TTP) for blood culture bottles incubated in the BacT/Alert Virtuo instrument was compared to the BacT/Alert 3D. TTP was significantly shorter with the Virtuo (median 16.2 h) than 3D (median 21.1 h; P < 0.001). Switching from 3D to Virtuo significantly improved TTP in this multicenter hospital setting study. IMPORTANCE Sepsis affects millions of people around the world each year, and accounts for a significant number of deaths in hospital intensive care units (ICU). Timely diagnosis is key to decreasing morbidity and mortality. One important element of sepsis diagnosis is organism detection using blood cultures. In this study, we examined the impact of implementing the BacT/Alert Virtuo automated blood culture detection system on time to positivity in an ICU patient population at a multicenter hospital setting.

Impact of Automated Blood Culture Systems on the Management of Bloodstream Infections: Results from a Crossover Diagnostic Clinical Trial

Bloodstream infections are associated with high rates of morbidity and mortality. Blood culture remains the gold standard for the diagnosis of BSIs. We report a prospective crossover diagnostic clinical trial comparing the performances of two blood culture incubation systems: Virtuo and Bactec FX. The primary outcome was the time to detection (TTD) (from the loading of the sample into the incubator to the positivity signal). Patients over 16 years old suspected of having bacteremia/fungemia were included. They were divided into two strata with a total of 9,957 blood extractions. Initially, each stratum was randomly assigned to one of the incubators and then alternated every 2 weeks for 6 months. Each sample was inoculated into an aerobic bottle and an anaerobic bottle. All bottles were processed equally according to the laboratory's standard procedures after they were flagged positive. We analyzed 4,797 samples in the Virtuo system and 5,160 in the Bactec FX system. The median TTD was significantly lower for the Virtuo group (Virtuo, 15.2 h; Bactec FX, 16.3 h [P < 0.0001]). The turnaround time (TAT) (from sample loading to the Gram stain report) was also reduced with Virtuo (Virtuo, 26.2 h; Bactec FX, 28.3 h [P < 0.004]). When considering only samples from patients with antimicrobial treatment prior to blood culture extraction, the TTD was shorter for Virtuo (median differences in the TTD of 4.5 h for all bottles and 8.7 h for aerobic bottles only [P = 0.0001]). In conclusion, virtuo provided shorter TTD and TAT than Bactec FX. The difference in the median TTD was increased when considering samples incubated in aerobic bottles from patients with antimicrobial treatment. This could have an important effect on the faster diagnosis of BSIs. IMPORTANCE Bloodstream infections are associated with high rates of morbidity and mortality. Blood culture remains the gold standard for its diagnosis. While the identification of the pathogen and its antibiotic susceptibility is required to confirm the optimal antimicrobial regimen, reductions in the times to the detection of positivity and reporting of Gram stain results may be important and time-saving to reduce inappropriate antimicrobial use, improve patient outcomes, and decrease health care costs. We report the first clinical diagnostic study of this scale in a "real-world" setting with a crossover design, comparing two automatic blood culture incubators using samples from patients with a suspected diagnosis of bacteremia/sepsis, as opposed to spiked vials. Our study design mimics that of clinical trials performed for drug marketing authorization, but patient randomization was replaced with the crossover design. A shorter time to detection could have an important effect on the faster identification of causative microorganisms of BSIs and antimicrobial stewardship.

Routine Use of Anaerobic Blood Culture Bottles for Specimens Collected from Adults and Children Enhances Microorganism Recovery and Improves Time to Positivity

The utility of anaerobic blood culture bottles remains controversial, especially for specimens from children. Data are limited on the inclusion of an anaerobic bottle as part of a blood culture "set" when using contemporary blood culture instruments and media. Here, we evaluated the clinical utility of anaerobic blood culture bottles (FN Plus) and aerobic bottles (FA Plus) for the BacT/Alert Virtuo blood culture system (bioMérieux). A total of 158,710 bottles collected between November 2018 and October 2019 were evaluated. There were 6,652 positive anaerobic bottles, of which 384 (5.8%) contained 403 obligate anaerobes. In patients <19 years old, there were 389 positive anaerobic bottles, with 15 (1.8%) containing 16 obligate anaerobes. If not for anaerobic bottles, all but 8 obligate anaerobes would have gone undetected. Furthermore, anaerobic bottles were advantageous for some facultative anaerobes. Staphylococcus aureus from anaerobic bottles demonstrated statistically significant increased recovery (1,992 anaerobic versus 1,901 aerobic bottles, P = 0.009) and faster mean time to positivity (1,138 versus 1,174 min, P = 0.027). Only 25 microorganisms had statistically significant improved recovery and/or faster time to positivity from aerobic versus anaerobic bottles, suggesting anaerobic bottles offer comparable growth for most species. Finally, if only an aerobic bottle had been collected, 2,027 fewer positive cultures would have been detected and 7,452 fewer isolates would have been reported, including cultures with S. aureus (413 isolates, 10.6% less), Pseudomonas aeruginosa (9 isolates, 3.1% less) and Escherichia coli (193 isolates, 14.0% less). Taken together, these findings support the practice of routinely including an anaerobic bottle for blood culture collection.

Clinical Significance of BD Bactec FX Blood Culture Incubation Beyond 96 Hours (4 Days)

Blood cultures (BC) for bacteria and yeast have traditionally been incubated for 5 days using modern instruments. Many organisms may grow sooner, and the need for the full 5-day incubation period has been questioned. This study evaluated the clinical significance of isolates recovered beyond 96 h. A retrospective chart review was conducted on all positive BC (+BC) performed via BD Bactec FX with >96 h of incubation from 5/2019 to 1/2022 at the UW Health University Hospital clinical microbiology laboratory. A total of 59,958 BC were performed; 6,031 (10%) were +BC. Of +BC, 104 (2%) demonstrated growth >96 h. The 104 cultures were from 89 patients and included 12 (12%) Staphylococcus aureus (1 MRSA), 9 (9%) yeast (8 Candida sp.), 8 (8%) Escherichia coli and 7 (7%) Enterococcus sp. (1 VRE) isolates. Fifty-six percent (n = 50) of the 89 +BC >96 h cases were clinically significant, and 26% (n = 13) resulted in antibiotic adjustments based on the +BC; 4 of these had previous positive cultures. Of the remaining 37 clinically significant +BC >96 h for which no antibiotic changes were made, 32 patients had previous positive cultures. The majority (98%) of BC bottles were positive before 96 h. For isolates that required >96 h, most (56%) were considered clinically significant, including S. aureus and E. coli cultures. Changes to antibiotic therapy were made in a minority (26%) of clinically significant cases. Based on these findings, under routine conditions, laboratories using BD Bactec FX should maintain a 120 h incubation period.

Clinical Impact of Time-to-Positivity of Blood Cultures on Mortality in Patients with Pseudomonas aeruginosa Bacteremia

OBJECTIVES

To investigate the impact of the time-to-positivity of blood cultures (TTP) on 30-day mortality in patients with Pseudomonas aeruginosa (PA) bacteremia.

METHODS

All non-duplicated episodes of PA monomicrobial bacteremia in adult patients from January 2013 to February 2020 were analysed. Epidemiological and clinical data were collected. TTP for PA isolates was automatically recorded. Multivariate analysis identified factors predicting 30-day overall mortality.

RESULTS

A total of 328 patients were identified. The median TTP for PA isolates was 15 h (IQR 12-18 h). All MDR/XDR episodes were positive within the first 36 h. The 30-day mortality rate was 32.3%. The best cut-off value of the TTP for predicting mortality was 16 h (AUC 0.62, 95% CI 0.56-0.67, P=0.001). The 30-day mortality rate was significantly higher in the TTP ≤16 h group (41.0% versus 19.5%, P<0.001). In a multivariate analysis, severe neutropenia (aOR 2.67, 95% CI 1.4-5.09, P=0.002), septic shock (aOR 3.21, 95% CI 1.57-5.89, P<0.001), respiratory source (aOR 4.37, 95% CI 2.24-8.52, P<0.001), nosocomial acquisition (aOR 1.99, 95% CI 1.06-3.71, P=0.030), TTP≤ 16 h (aOR 2.27, 95% CI 2.12-4.25, P=0.010) and MDR/XDR phenotype (aOR 2.54, 95% CI 1.38-4.67, P=0.002) were independently associated with 30-day mortality.

CONCLUSIONS

A short TTP (≤16 h) was independently associated with increased 30-day mortality. After local validation, this routinely microbiological parameter might be useful for guiding empirical antipseudomonal therapies and supporting the close monitoring of patients with PA bacteremia.

The Impact of Implementing the Virtuo Blood Culture System on the Characteristics and Management of Patients with Staphylococcus aureus Bacteremia

Persistent Staphylococcus aureus bacteremia (SAB) has been associated with increased mortality. Enhanced microbial detection with new blood culture technology may improve detection of S. aureus in patients with SAB. We performed a 24-month retrospective study of hospitalized adults with SAB and an infectious diseases consult comparing two time periods pre- (January to December 2018) and postimplementation (January to December 2019) in which the VersaTREK and BacT/Alert Virtuo blood culture systems were used, respectively. Measurements included SAB duration, time to positivity, source of bacteremia, antimicrobial therapy, and mortality. A total of 416 episodes of SAB occurred during the study period: 176 (42%) pre- and 240 (58%) postimplementation. Patients in both periods had similar clinical characteristics; however, patients in the postimplementation period were more likely to have intermediate (3 to 6 days; 23% versus 40%; P < 0.001) and prolonged SAB duration (>7 days; 4% versus 14%; P < 0.001). Combination antistaphylococcal therapy was more frequent postimplementation (6.3% pre- versus 15.8% postimplementation; P = 0.003), and the median time to source control was shorter (4 versus 2 days; P = 0.02). Median time to positivity for the index blood culture was shorter postimplementation (17.8 h pre- versus 13.3 h postimplementation; P < 0.001). There was no difference in 90-day all-cause readmissions (51% versus 44%; P = 0.11) or mortality (32% versus 32%; P = 0.95). An increased frequency of prolonged SAB with increased use of combination antistaphylococcal therapy was noted with implementation of a new blood culture system, likely secondary to the blood culture media; however, no differences on adverse outcomes were noted.

Detection of Microorganisms in Body Fluids via MTT-PMS Assay

Early detection of microorganisms is essential for the management of infectious diseases. However, this is challenging, as traditional culture methods are labor-intensive and time-consuming. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide-phenazine methosulfate (MTT-PMS) assay has been used to evaluate the metabolic activity in live cells and can thus be used for detecting living microorganisms. With the addition of NaOH and Tris-EDTA, the same approach can be accelerated (within 15 min) and used for the quick detection of common bacterial pathogens. The assay results can be evaluated colorimetrically or semi-quantitatively. Here, the quick detection by MTT-PMS assay was further investigated. The assay had a detection limit of approximately 104 CFU/mL. In clinical evaluations, we used the MTT-PMS assay to detect clinical samples and bacteriuria (>105 CFU/mL). The negative predictive value of the MTT-PMS assay for determining bacteriuria was 79.59% but was 100% when the interference of abnormal blood was excluded. Thus, the MTT-PMS assay might be a potential "rule-out" tool for bacterial detection in clinical samples, at a cost of approximately USD 1 per test. Owing to its low cost, rapid results, and easy-to-use characteristics, the MTT-PMS assay may be a potential tool for microorganism detection.

Real World Evaluation of the Impact of Implementation of the VIRTUO Blood Culture System in a Tertiary Care Hospital

The bioMerieux BACT/ALERT VIRTUO (VIRTUO) blood culture system used in combination with resin-containing media may enhance the growth of microorganisms. Our objective was to assess the impact of transitioning to the VIRTUO system in comparison to the VersaTREK blood culture system at a tertiary care medical center. We retrospectively reviewed all blood cultures performed at a 1250-bed academic medical center between January-December 2018 (VersaTREK) and January-December 2019 (VIRTUO). Blood culture positivity rates and contamination rates were compared pre- versus post-VIRTUO implementation. Of 101,438 blood cultures performed during the study period, 48,839 (48.1%) were processed pre-implementation and 52,599 (51.9%) post-implementation. The blood culture positivity rate increased from 8.1% pre-implementation to 11.7% post-implementation (p<0.001). Staphylococcus aureus was the most frequently isolated species in both time periods and had higher recovery rate post-implementation (1.5% of all blood cultures obtained pre- vs. 3.4% post-implementation, p<0.001). A higher recovery rate in the post-implementation period was also noted for coagulase-negative staphylococci (1.9% pre- vs. 2.7% post-implementation, p<0.001), as well as modest but statistically significant changes for E. coli (0.8% vs. 1.0%, p<0.001), K. pneumoniae (0.4% vs. 0.5%, p=0.005) and Candida albicans. (0.1% vs. 0.2%, p=0.038). The inpatient blood culture contamination rate was higher post-implementation (1.5% pre- vs. 1.9% post-implementation, p<0.001). The VIRTUO blood culture system was associated with a higher observed proportion of positive blood cultures compared to the previous VersaTREK system. Future studies are needed to assess whether an increased rate of positive blood cultures is associated with changes in clinical outcomes.

Comparison of Microorganism Detection and Time to Positivity in Pediatric and Standard Media from Three Major Commercial Continuously Monitored Blood Culture Systems

New blood culture instrumentation and medium formulations have led to improved time to positivity (TTP) for positive blood cultures. Data regarding the necessity of pediatric blood culture bottles with contemporary blood culture systems are sparse. We compared performance of three commercial blood culture systems, evaluating impact of blood volumes in standard and pediatric blood culture media across systems. Simulated blood cultures with packed red blood cells (PRBCs) and three Gram-positive, four Gram-negative, and one anaerobic organism (final concentrations ranging from 0.5 to 19 CFU/ml blood) on the Virtuo, VersaTrek, and Bactec FX instruments were evaluated with FAN Plus, Redox, and Bactec Plus media, respectively. For each medium/instrument/organism combination, 1-, 3-, 5-, and 10-ml blood volumes were evaluated in triplicate. Detection rate was not affected by blood volume. Aerobic organisms that demonstrated variable rates of detection were Kingella kingae, Haemophilus influenzae, and Neisseria meningitidis. Bacteroides fragilis was detected in 83%, 100%, and 100% of Virtuo, VersaTrek, and Bactec anaerobic bottles, respectively. The average TTP of standard medium for aerobic organisms detected on Virtuo was decreased compared to those for VersaTrek (-2.3 h) and Bactec (-4.9 h). Compared to standard medium, detection rate and TTP were unchanged on Virtuo, while TTP was reduced with pediatric medium for 2/8 organisms tested on Bactec and 7/8 organisms on VersaTrek, illustrating the potential benefit of pediatric medium on VersaTrek or Bactec when low blood volumes (<5 ml) are collected. These results demonstrate that TTP is decreased on the Virtuo compared to VersaTrek and Bactec for many microorganisms associated with bloodstream infection (BSI) but may have species-specific limitations.

Impact of 24/7 loading of blood culture bottles in a new automated incubator on the diagnosis of bloodstream infections

Blood culturing (BC) remains the gold standard for bloodstream diagnosis but its workflow is slow. We aimed reducing this time by implementing a new automated incubator with a 24/7 BC workflow. With this new strategy, time to incubation was shorter (1.52 h vs 6.82 h), positivity rates were higher (10.6% vs 8.9%, p<0.05), and the number of BSI diagnostics increased (16.1% vs 13.8% patients and 2.3 vs 1.9 density episode per 1000 hospital days). Our results show that implementing automatic loading of BC bottles with a 24/7 strategy not only shortened time to diagnosis but significantly increased the BSI diagnosis rate.

Evaluation of Optimal Blood Culture Incubation Time To Maximize Clinically Relevant Results from a Contemporary Blood Culture Instrument and Media System

Timely diagnosis of microorganisms in blood cultures is necessary to optimize therapy. Although blood culture media and systems have evolved for decades, the standard interval for incubation prior to being discarded as negative has remained 5 days. Here, we evaluated the optimal incubation time for the BacT/Alert Virtuo blood culture detection system (bioMérieux) using FA Plus (aerobic) and FN Plus (anaerobic) resin culture bottles in routine clinical use.

Timely diagnosis of microorganisms in blood cultures is necessary to optimize therapy. Although blood culture media and systems have evolved for decades, the standard interval for incubation prior to being discarded as negative has remained 5 days. Here, we evaluated the optimal incubation time for the BacT/Alert Virtuo blood culture detection system (bioMérieux) using FA Plus (aerobic) and FN Plus (anaerobic) resin culture bottles in routine clinical use. Following institutional review board (IRB) approval, a retrospective review evaluated the outcomes of 158,710 bottles collected between November 2018 and October 2019. The number of positive blood bottles was 13,592 (8.6%); 99% of positive aerobic and anaerobic bottles flagged positive by 91.5 and 108 h, respectively. The mean (median) times to positivity were 18.4 h (15.6 h) for Staphylococcus aureus, 12.3 h (9.5 h) for Escherichia coli, 22.2 h (15.9 h) for Pseudomonas aeruginosa, and 48.9 h (42.9 h) for Candida spp. Only 175 bottles (0.1% of all bottles) flagged positive after 4 days of incubation; 89 (51%) of these bottles grew Cutibacterium (Propionibacterium) species. Chart review of blood cultures positive after 4 days (96 h) rarely had a clinical impact and sometimes had a negative impact on patient care. Finally, a seeded study of the HACEK group (i.e., Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella), historically associated with delayed blood culture positivity, demonstrated no benefit to extended incubation beyond 4 days. Collectively, these findings demonstrated that a 4-day incubation time was sufficient for the Virtuo system and media. Implementation of the 4-day incubation time could enhance clinically relevant results by reducing recovery of contaminants and finalizing blood cultures 1 day earlier.

Comparison of time-to-positivity between two blood culture systems: a detailed analysis down to the genus-level

A recently developed, automated blood culture system and medium improve the time-to-positivity (TTP) for bacteremia. However, there have thus far been no genus-level analyses using this novel system. We evaluated and compared the changes in blood culture TTP between two systems: BacT/Alert 3D with a blood culture medium containing activated charcoal versus the more recent BacT/Alert Virtuo with a blood culture medium containing polymeric beads. This before-and-after study included blood cultures collected between July 2010 and April 2014 (3D, activated charcoal) and between July 2015 and April 2018 (Virtuo, polymeric beads). A total of 554,732 blood cultures were included, 267,935 (48.30%) during the first period and 286,797 (51.70%) during the second period. Overall, 55,611 (10.02%) tested positive for at least one microorganism. The incubation of the blood culture medium in the Virtuo system was associated with reduced TTP for the most prevalent bacteria, those representing 91.72% (n=51,006) of all the positive blood cultures. The median TTP was reduced by 0.99 h for Staphylococcus, Enterococcus, Streptococcus, Pseudomonadales, and most of the genera within the order Enterobacterales (except the family Morganellaceae). However, strictly anaerobic bacteria belonging to the genus Bacteroides, representing 0.85% (n=474) of all positive blood cultures, were detected 4.53 h later using the Virtuo system. Virtuo was associated with a shorter TTP for most bacteria, but this improvement was heterogeneous to the genus level.

Prebiotic Colloidal Oat Supports the Growth of Cutaneous Commensal Bacteria Including S. epidermidis and Enhances the Production of Lactic Acid

Background

Multiple skin conditions have been associated with alterations in the diversity and composition of the skin microbiome, including dry skin and atopic dermatitis. In these conditions, a number of commensal skin bacteria have been implicated in supporting a healthy skin barrier, including Staphylococcus epidermidis. Recent clinical studies in patients with mild-to-moderate atopic dermatitis and dry/itchy skin have shown significantly improved skin barrier function and microbial diversity upon treatment with moisturizers containing 1% colloidal oat. We hypothesized that direct use of colloidal oat by skin microbes contributes to these therapeutic benefits.

Methods

Skin bacterial growth was assessed using the BacT/ALERT system. Staphylococcus aureus and S. epidermidis growth rates and metabolism were compared in an in vitro competition assay. The effect of a 1% colloidal oat-containing moisturizer on lactic acid content of the stratum corneum was clinically assessed in subjects with moderate-to-severe dry skin. S. epidermidis gene expression was evaluated by next-generation mRNA sequencing. Short-chain fatty acids were quantified in bacterial culture supernatants.

Results

In vitro, colloidal oat increased the growth rate of S. epidermidis vs S. aureus, as well as the metabolism of S. epidermidis. Colloidal oat also significantly increased lactic acid concentrations in supernatants of both strains and decreased pH, consistent with clinical findings that 6-week use of a 1% colloidal oat-containing lotion significantly increased lactic acid on dry skin. Further analyses suggest that colloidal oat alters the gene expression profile of S. epidermidis.

Conclusion

Colloidal oat directly affects the growth, metabolism, lactic acid production, and gene expression of skin commensal bacteria, as shown via in vitro studies. The increased production of lactic acid reflects clinical observations with colloidal oat-containing skin moisturizers. Our findings suggest a new mechanism for colloidal oat as a skin prebiotic, which may contribute to improvements in skin and microbiome diversity in various skin conditions, including dry/itchy skin and atopic dermatitis.

Comparison of Rapid and Routine Methods of Identification and Antibiotic Susceptibility Testing of Microorganisms from Blood Culture Bottles

Reporting of the results of routine laboratory blood culture tests to clinicians is vital to the patients’ early treatment. This study aimed to perform identification and antibiotic susceptibility tests of the blood cultures showing positive signals of microbial growth in the first 12 hours of incubation by using centrifugation and Gram staining of 5 ml of liquid from the vial, thus achieving faster results. This study included 152 consecutively incubated blood culture samples showing positive microbial growth signals in the first 12 hours. The samples were centrifuged and then categorized into two groups (Gram-positive and Gram-negative) using Gram staining. Identification and antibiotic susceptibility tests were performed using an automated culture antibiogram device. For routine processing, media inoculated with positive blood culture were kept in the incubator for at least 24 hours. To compare the two methods in terms of the bacteria identification, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) of the growing colony was studied. By Gram staining, the same bacterial strains were obtained for 138 (92%) of the 152 samples, similar to the results of the procedures mentioned earlier. With the samples tested with both methods, the antibiotic susceptibility profiles were compared using the antibiogram results for 1,984 samples that underwent the antibiotic testing. A 97.4% (for 1,934 antibiotic susceptibility assays) agreement was observed between the two methods. Comparing the results of the post-centrifugation Gram staining to those obtained for the specimens using routine procedures, the clinicians reported a high success rate (approximately 97%).

Effect of delayed entry on performance of the BACT/ALERT FAN PLUS bottles in the BACT/ALERT VIRTUO blood culture system

Delayed entry of patient blood culture samples into a microbial detection system is unavoidable at times, due to off-shift staffing or transporting samples to centralized laboratories. Pre-incubation time and temperature of blood culture bottles are the most critical factors impacting recovery and detection of microorganisms. A total of 1377 BACT/ALERT® (BTA) Fastidious Antimicrobial Neutralization (FAN® PLUS) bottles (FA PLUS, FN PLUS, and PF PLUS) were tested after delayed entry times of 24 and 36 h at 20–25 °C (room temperature, RT) prior to loading into the BACT/ALERT® VIRTUO® microbial detection system (VIRTUO). Clinically relevant organisms were inoculated into bottles with 5–84 colony forming units (CFU) per bottle, and human blood (0 to 10 mL), and then loaded into the VIRTUO. When bottles were loaded without delay, a mean time to detection (TTD) of 9.6 h was observed. For delayed bottles, the TTD reported by the VIRTUO was added to the 24-h and 36-h delay times and resulted in average time to results of 32.5 h and 42.5 h, respectively. The FAN PLUS bottles in conjunction with the VIRTUO produced acceptable results when delays up to 24 h at 20–25 °C occur in loading.

Modern Blood Culture: Management Decisions and Method Options

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

Improved blood culture workflow in the time to detection of microorganisms placing incubators systems outside of microbiology laboratory

PURPOSE

We analyzed the workflow of the blood culture procedure with one blood culture incubator in the microbiology laboratory, in comparison with the workflow with the incubators systems placing outside, and in a microbiology laboratory without 24-h staffing.

METHODS

We assessed the elapsed time (ET) and time-to-result (TTR) in the two laboratory workflows during 1 month period in consecutive years. First period with one BACT/ALERT 3D module located in the microbiology laboratory (ML) (access 8 a.m. to 10 p.m.) and second period with three BACT/ALERT VIRTUO modules (one located in ML and two in the core sample laboratory, access 24 h).

RESULTS

The mean ET with BACT/ALERT 3D was 7.09 ± 6.15 h and 1.32 ± 3.14 h with BACT/ALERT VIRTUO. During the 8:00 a.m. to 10:00 p.m. shift, the average ETs were 3.54 ± 5.06 vs 1.59 ± 1.29 h for the two time periods, respectively. Since the automated loading of bottles on the BACT/ALERT VIRTUO allows processing of blood cultures during the night shift, there was a significant reduction of time during the 10:00 p.m. to 8:00 a.m. shift, where the average ET was 10.52 ± 5.23 vs 1.00 ± 4.40 h, respectively. The percentage of positivity in the first period was 9.03% and 11.18% in the second (p = 0.0003). The average TTR in the first period was 24.78 ± 15.9 h and 16.85 ± 14.13 h in the second (p < 0.0001).

CONCLUSIONS

Easy 24-h access to blood culture incubators resulted in significant improvement in the workflow of blood culture, decreasing ET, and therefore decreasing the time to positivity and the efficiency of recovery.

A comparative evaluation of BACT/ALERT FA PLUS and FN PLUS blood culture bottles and BD BACTEC Plus Aerobic and Anaerobic blood culture bottles for antimicrobial neutralization

The performance of BACT/ALERT FA and FN PLUS (FA PLUS and FN PLUS) blood culture bottles with the BACT/ALERT VIRTUO (bioMérieux, Inc., Durham, NC) and BD BACTEC Plus Aerobic and Anaerobic (BD Aerobic and BD Anaerobic) blood culture bottles with the BD BACTEC FX (BD Diagnostics, Sparks, MD) for antimicrobial neutralization at peak serum concentration was evaluated. The following antibiotic agents and microbial strains were used: ampicillin, cefepime, cefotaxime, gentamicin, levofloxacin, meropenem, piperacillin-tazobactam, and vancomycin; methicillin-sensitive Staphylococcus aureus, Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Bacteroides fragilis. The detection rate of FA PLUS bottles was 69.1% (259/375) and that of BD Aerobic bottles was 75.5% (283/375) (p = 0.050). In the case of anaerobic culture, the overall detection rate of FN PLUS bottles was 77.0% (231/300) and that of BD Anaerobic bottles was 71.3% (214/300) (p = 0.113). The time to detection (TTD) from aerobic culture was 2.8 h shorter in FA PLUS bottles (12.4 h) compared to BD Aerobic bottles (15.2 h) (p < 0.001). And the TTD from anaerobic culture was 1.6 h shorter in FN PLUS bottles (18.1 h) compared to BD Anaerobic bottles (19.7 h) (p = 0.061). The FA PLUS bottles exhibited a lower detection rate compared to BD Aerobic bottles, while FN PLUS bottles showed a higher detection rate compared to BD Anaerobic bottles. The BACT/ALERT VIRTUO system exhibited shorter TTD compared to the BD BACTEC FX system for both aerobic and anaerobic cultures.

Culturing periprosthetic tissue in BacT/Alert® Virtuo blood culture system leads to improved and faster detection of prosthetic joint infections

Background

Blood culture bottles (BCBs) provide a semiautomated method for culturing periprosthetic tissue specimens. A study evaluating BCBs for culturing clinical samples other than body fluids is needed before implementation into clinical practice. Our objective was to evaluate use of the BacT/Alert® Virtuo blood culture system for culturing periprosthetic tissue specimens.

Methods

The study was performed through the analysis of spiked (n = 36) and clinical (n = 158) periprosthetic tissue samples. Clinical samples were analyzed by the BCB method and the results were compared to the conventional microbiological culture-based method for time to detection and microorganisms identified.

Results

The BacT/Alert® Virtuo blood culture system detected relevant bacteria for prosthetic joint infection in both spiked and clinical samples. The BCB method was found to be as sensitive (79%) as the conventional method (76%) (p = 0.844) during the analyses of clinical samples. The BCB method yielded positive results much faster than the conventional method: 89% against 27% detection within 24 h, respectively. The median detection time was 11.1 h for the BCB method (12 h and 11 h for the aerobic and the anaerobic BCBs, correspondingly).

Conclusion

We recommend using the BacT/Alert® Virtuo blood culture system for analyzing prosthetic joint tissue, since this detect efficiently and more rapidly a wider range of bacteria than the conventional microbiological method.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-4206-x) contains supplementary material, which is available to authorized users.

Comparison of Clinical Performance Between BacT/Alert Virtuo and BacT/Alert 3D Blood Culture Systems

BACKGROUND

BacT/Alert Virtuo (BioMérieux, Durham, NC, USA) is a recently developed blood culture system that includes functions of automatic registration, loading, and unloading of the blood culture bottles, as well as measurement of blood volume. We compared the performances between the BacT/Alert Virtuo and 3D (BioMérieux) blood culture systems.

METHODS

A total of 952 patients (1,904 sets) visiting an university-affiliated hospital in Korea for blood cultures were enrolled. Five milliliters of blood was added into each of the two aerobic (FA Plus) and two anaerobic (FN Plus) bottles of the Virtuo and 3D systems for a single set. Positive rate and time to detection (TTD) were compared between the two systems.

RESULTS

The positive rates were 8.3% and 8.4% in FA Plus bottles and 7.8% and 8.3% in FN Plus bottles, in the Virtuo and 3D systems, respectively (P>0.05). Median TTDs were shorter in the Virtuo than in the 3D system for all isolates (11.5 hours [N=305] vs 11.8 hours [N=318], P<0.001), Staphylococcus aureus (N=38; 14.3 hours vs 16.0 hours, P=0.021), and Escherichia coli (N=117; 10.4 hours vs 11.0 hours, P<0.001).

CONCLUSIONS

The Virtuo has the potential to detect pathogens early in all bottle types. This might improve the prognosis of sepsis by allowing for implementation of expeditious management.

In vitro Evaluation of BACT/ALERT® VIRTUO®, BACT/ALERT 3D®, and BACTEC™ FX Automated Blood Culture Systems for Detection of Microbial Pathogens Using Simulated Human Blood Samples

Blood culture (BC) is still the standard for diagnosing bloodstream infections (BSIs), especially those caused by bacteria and fungi. Infection-complicating sepsis or septic shock often occurs at BSI onset, making necessary to improve the diagnostic yield of positive BCs. Among the BC systems currently available, the BACT/ALERT® VIRTUO® (VIRTUO) system has been developed to shorten time to detection (TTD) of positive BCs. In this study, we assessed TTD for 330 clinically relevant species including 14 Gram-positive, 14 Gram-negative, and 5 yeast isolates in spiked human blood samples that were tested in parallel with VIRTUO BACT/ALERT® 3D (BTA3D) and BACTEC™ FX (BACTEC) systems. We inoculated 30 colony-forming unit (CFU) from each microbial suspension into BACT/ALERT® Plus or BACTEC™ Plus (aerobic/anaerobic or pediatric) BC bottles, and we used two different blood volumes to simulate, respectively, the BCs collected from adult and pediatric patients. Of 2,610 bottles tested, 2,600 (99.6%) signaled positive in the three systems. Only the BACTEC system did not detect Staphylococcus lugdunensis isolates in anaerobic bottles. Among adult simulated cultures, the median TTD was significantly shorter for aerobic/anaerobic bottles incubated in VIRTUO (11.6 h and 10.1 h) compared to bottles incubated in either BTA3D (13.3 and 12.3 h) or BACTEC (13.5 and 12.2 h) system. Among pediatric simulated cultures, the median TTD was significantly shorter for bottles incubated in VIRTUO (11.2 h) compared to bottles incubated in either the BTA3D (13.0 h) or BACTEC (12.5 h) system. Compared to BTA3D and/or BACTEC systems, VIRTUO allowed faster growth detection for most of the 33 microbial species tested. Notable examples were Salmonella spp. (7.4 h by VIRTUO vs. 10.1 h and 9.2 h by either BTA3D or BACTEC) and Streptococcus agalactiae (8.1 h by VIRTUO vs. 10.3 and 9.4 h by either BTA3D or BACTEC). The few notable exceptions included Stenotrophomonas maltophilia and some Candida species. Together, these findings confirm that VIRTUO has greater potential of improving the laboratory detection of bacteremia and fungemia than the progenitor BTA3D or the competitor BACTEC system.

Clinical Performance Evaluation of VersaTrek 528 Blood Culture System in a Chinese Tertiary Hospital

Background: The aim of this study was to evaluate the clinical performance of VersaTrek 528 compared to BACTEC FX 400 blood culture (BC) systems.

Materials and Methods: Simulated and clinically obtained BCs were used in the study. Confirmed bacterial species (n = 78), including 43 Gram-positives, 30 Gram-negatives, and 5 Candida albicans strains, were each inoculated into BC bottles. Clinically obtained BCs were subdivided into two groups, A and B. In group A were 72 BC sets (pair: aerobic and anaerobic) in which a set inoculated with 5 ml blood was processed in the VersaTrek BC system, whilst the one inoculated with 10 ml blood was processed in the FX BC system. In group B, 76 BC sets (pairs) corresponding to 152 VersaTrek bottles and 152 FX bottles were inoculated with the same volume (10 ml) of blood, and processed in each system.

Results: In the simulated BC study, 90% (63/70) of the VersaTrek aerobic bottles were positive, which was higher than that of FX 400 (59/70, 84%), but was not statistically significant (P = 0.423). In contrast, FX 400 anaerobic bottles had a higher positive rate than the other BC system (84 vs. 77%), although it was statistically insignificant (P = 0.267). Time to detection of organisms in the two BCs was comparable for both aerobic (P = 0.131) and anaerobic bottles (P = 0.104). In clinical BCs of group A, FX BC system had slightly higher positive rates for both aerobic (11.1 vs. 9.7%, P = 0.312) and anaerobic (8.3 vs. 6.9%, P = 0.375) bottles. However, the difference was not statistically significant. In group B, VersaTrek aerobic bottles had a higher positive rate compared to the other BC system (10.5 vs. 5.2%, P = 0.063). In terms of positive rates of sub-studies A and B, VersaTrek and FX BC systems were comparable.

Conclusion: There was no significant difference between the two BC systems in the detection of bacteria and fungi in simulated BCs. In clinical BCs, the performance of the VersaTrek BC system, with inoculation of 5 or 10 ml patient’s blood, was comparable to the FX system with inoculation of 10 ml patient’s blood.

Time-to-detection of bacteria and yeast with the BACTEC FX versus BacT/Alert Virtuo blood culture systems

BACKGROUND

Bloodstream infections are associated with high rates of morbidity and mortality. Rapid detection of bloodstream infections is important in achieving better patient outcomes.

OBJECTIVE

Compare the time-to-detection (TTD) of the new BacT/Alert Virtuo and the BACTEC FX automated blood culture systems.

DESIGN

Prospective simulated comparison of two instruments using seeded samples.

SETTING

Medical microbiology laboratory.

METHODS

Blood culture bottles were seeded in triplicate with each of the standard ATCC strains of aerobes, anaerobes and yeast. TTD was calculated as the length of time from the beginning of culture incubation to the detection of bacterial growth.

MAIN OUTCOME MEASURES

TTD for the various tested organisms on the two microbial detection systems.

RESULTS

The 99 bottles of seeded blood cultures incubated in each of the blood culture systems included 21 anaerobic, 39 aerobic and 39 pediatric bottles. The BacT/Alert Virtuo system exhibited significantly shorter TTD for 72.7 % of the tested organisms compared to BACTEC FX system with a median difference in mean TTD of 2.1 hours (interquartile range: 1.5-3.5 hours). The BACTEC FX system was faster in 15.2% (5/33) of microorganisms, with a median difference in mean TTD of 25.9 hours (IQR: 9.1-29.2 hours).

CONCLUSION

TTD was significantly shorter for most of the microorganisms tested on the new BacT/Alert Virtuo system compared to the BACTEC FX system.

LIMITATIONS

Use of simulated cultures to assess TTD may not precisely represent clinical blood cultures.

CONFLICT OF INTEREST

None.

Simultaneous Detection of Key Bacterial Pathogens Related to Pneumonia and Meningitis Using Multiplex PCR Coupled With Mass Spectrometry

Pneumonia and meningitis continue to present an enormous public health burden and pose a major threat to young children. Among the causative organisms of pneumonia and meningitis, bacteria are the most common causes of serious disease and deaths. It is challenging to accurately and rapidly identify these agents. To solve this problem, we developed and validated a 12-plex PCR coupled with matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) method (bacterial pathogen-mass spectrometry, BP-MS) that can be used to simultaneously screen for 11 key bacterial pathogens related to pneumonia and meningitis. Forty-six nasopharyngeal swabs and 12 isolates were used to determine the specificity of the method. The results showed that, using the BP-MS method, we could accurately identify the expected bacteria without cross-reactivity with other pathogens. For the 11 target bacterial pathogens, the analytical sensitivity of the BP-MS method was as low as 10 copies/reaction. To further evaluate the clinical effectiveness of this method, 204 nasopharyngeal swabs from hospitalized children with suspected pneumonia were tested using this method. In total, 81.9% (167/204) of the samples were positive for at least one of the 11 target pathogens. Among the 167 bacteria-positive samples, the rate of multiple infections was 55.7% (93/167), and the most frequent combination was Streptococcus pneumoniae with Haemophilus influenzae, representing 46.2% (43/93) two-pathogen mixed infections. We used real-time PCR and nested PCR to confirm positive results, with identical results obtained for 81.4% (136/167) of the samples. The BP-MS method is a sensitive and specific molecular detection technique in a multiplex format and with high sample throughput. Therefore, it will be a powerful tool for pathogen screening and antibiotic selection at an early stage of disease.