Controlled clinical laboratory comparison of BACTEC plus aerobic/F resin medium with BacT/Alert aerobic FAN medium for detection of bacteremia and fungemia

Recovery of pathogens with implementation of a weight-based algorithm for pediatric blood cultures: an observational intervention study

BACKGROUND

Recovering pathogenic bacteria and yeast from pediatric blood cultures and reliably distinguishing between pathogens and contaminants are likely to be improved by increasing the volume of blood submitted to microbiology laboratories for culturing beyond the low volumes that have historically have been used. The primary aim of this study was to assess whether the pathogen recovery rate would increase after implementation of a weight-based algorithm for determining the intended volume of blood submitted for culturing. Secondary aims were to: 1) evaluate the effects of the algorithm implementation on the blood culture contamination rate; 2) determine whether pathogens might be found more often than contaminants in several as opposed to single bottles when more than one bottle is submitted; and 3) describe the microbiological findings for pathogens and contaminants in blood cultures by applying a clinical validation of true blood culture positivity.

METHODS

A pre-post comparison of positivity and contamination rates after increasing the theoretical blood volume and number of blood culture bottles was performed, on the basis of a clinical validation of blood culture findings as pathogens vs contaminants.

RESULTS

We examined 5327 blood cultures, including 186 with growth (123 true positives and 63 contaminated). The rate of true positive blood cultures significantly increased from 1.6% (42/2553) pre to 2.9% (81/2774, p = .002) post intervention. The rate of contaminated blood cultures did not change significantly during the study period (1.4% [35/2553] pre vs 1.0% [28/2774], p = .222) post intervention), but the proportion of contaminated cultures among all positive cultures decreased from 45% (35/77) pre to 26% (28/109, p = .005) post intervention. A microorganism that grew in a single bottle was considered a contaminant in 35% (8/23) of cases, whereas a microorganism that grew in at least two bottles was considered a contaminant in 2% (1/49, p < .001) of cases. According to common classification criteria relying primarily on the identity of the microorganism, 14% (17/123) of the recovered pathogens would otherwise have been classified as contaminants.

CONCLUSION

Implementation of a weight-based algorithm to determine the volume and number of blood cultures in pediatric patients is associated with an increase in the pathogen recovery rate.

Antibiotic stewardship for early-onset sepsis

Antibiotics are administered to the vast majority of preterm newborns and to a substantial proportion of term infants in the hours after birth due to risk for early-onset sepsis. The approaches taken to determine which newborns should be evaluated for early-onset sepsis, and what type and duration of antibiotics are administered, are important elements of neonatal antibiotic stewardship. The use of multivariate prediction models for sepsis risk assessment among infants born ≥35 weeks' gestation can safely reduce the use of empiric antibiotic therapy. Approaches incorporating serial physical examination may also contribute to decreasing empiric antibiotic exposure among such infants. Among infants born <35 weeks' gestation, delivery characteristics can be used to identify preterm infants at low enough risk of early infection that empiric therapies are not required. Data informing the epidemiology, microbiology and antibiotic susceptibility patterns of early-onset sepsis pathogens can be used to optimize antibiotic choice for empiric and targeted antibiotic therapy to ensure that effective therapies are administered, while decreasing the risks associated with broad-spectrum antibiotic exposure. Optimal use of blood culture and time to positivity data can also contribute to decreasing the risks associated with prolonged antibiotic administration in the face of sterile cultures.

Time to Positivity of Neonatal Blood Cultures for Early-onset Sepsis

BACKGROUND

In newborns at risk for early-onset sepsis, empiric antibiotics are often initiated while awaiting the results of blood cultures. The duration of empiric therapy can be guided by the time to positivity (TTP) of blood cultures. The objective of the study was to determine the TTP of neonatal blood cultures for early-onset sepsis and the factors which may impact TTP.

METHODS

Observational study of blood cultures growing pathogenic species obtained within 72 hours of birth from infants born at 23-42 weeks gestation, at 19 hospitals in Northern California, Boston, and Philadelphia. TTP was defined as the time from blood culture collection to the time organism growth was reported by the microbiology laboratory.

RESULTS

A total of 594 blood cultures growing pathogenic bacteria were identified. Group B Streptococcus and Escherichia coli accounted for 74% of blood culture isolates. Median TTP was 21.0 hours (interquartile range, 17.1-25.3 hours). Blood cultures were identified as positive by 24 hours after they were obtained in 68% of cases; by 36 hours in 94% of cases; and by 48 hours in 97% of cases. Neither the administration of maternal intrapartum antibiotic prophylaxis, gestational age <35 weeks, nor blood culture system impacted median TTP.

CONCLUSIONS

Pathogens are isolated by 36 hours after blood culture collection in 94% of neonatal early blood cultures, regardless of maternal antibiotic administration. TTP information can inform decisions regarding the duration of empiric neonatal antibiotic therapies.

Practical Guidance for Clinical Microbiology Laboratories: A Comprehensive Update on the Problem of Blood Culture Contamination and a Discussion of Methods for Addressing the Problem

In this review, we present a comprehensive discussion of matters related to the problem of blood culture contamination. Issues addressed include the scope and magnitude of the problem, the bacteria most often recognized as contaminants, the impact of blood culture contamination on clinical microbiology laboratory function, the economic and clinical ramifications of contamination, and, perhaps most importantly, a systematic discussion of solutions to the problem. We conclude by providing a series of unanswered questions that pertain to this important issue.

Management of Neonates Born at ≤34 6/7 Weeks' Gestation With Suspected or Proven Early-Onset Bacterial Sepsis

Early-onset sepsis (EOS) remains a serious and often fatal illness among infants born preterm, particularly among newborn infants of the lowest gestational age. Currently, most preterm infants with very low birth weight are treated empirically with antibiotics for risk of EOS, often for prolonged periods, in the absence of a culture-confirmed infection. Retrospective studies have revealed that antibiotic exposures after birth are associated with multiple subsequent poor outcomes among preterm infants, making the risk/benefit balance of these antibiotic treatments uncertain. Gestational age is the strongest single predictor of EOS, and the majority of preterm births occur in the setting of other factors associated with risk of EOS, making it difficult to apply risk stratification strategies to preterm infants. Laboratory tests alone have a poor predictive value in preterm EOS. Delivery characteristics of extremely preterm infants present an opportunity to identify those with a lower risk of EOS and may inform decisions to initiate or extend antibiotic therapies. Our purpose for this clinical report is to provide a summary of the current epidemiology of preterm neonatal sepsis and provide guidance for the development of evidence-based approaches to sepsis risk assessment among preterm newborn infants.

Management of Neonates Born at ≥35 0/7 Weeks' Gestation With Suspected or Proven Early-Onset Bacterial Sepsis

The incidence of neonatal early-onset sepsis (EOS) has declined substantially over the last 2 decades, primarily because of the implementation of evidence-based intrapartum antimicrobial therapy. However, EOS remains a serious and potentially fatal illness. Laboratory tests alone are neither sensitive nor specific enough to guide EOS management decisions. Maternal and infant clinical characteristics can help identify newborn infants who are at risk and guide the administration of empirical antibiotic therapy. The incidence of EOS, the prevalence and implications of established risk factors, the predictive value of commonly used laboratory tests, and the uncertainties in the risk/benefit balance of antibiotic exposures all vary significantly with gestational age at birth. Our purpose in this clinical report is to provide a summary of the current epidemiology of neonatal sepsis among infants born at ≥35 0/7 weeks' gestation and a framework for the development of evidence-based approaches to sepsis risk assessment among these infants.

Clinical Utility of Rapid Pathogen Identification for Detecting the Causative Organisms in Sepsis: A Single-Center Study in Korea

Purpose

The aim of this pre- and postintervention cohort study was evaluating how effectively rapid pathogen identification with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) detected the causative organisms in sepsis.

Methods

All consecutive adult patients who had bacteremia within 72 h of intensive care unit admission and met ≥2 quick Sequential Organ Failure Assessment criteria at intensive care unit admission were analyzed. The patients whose microorganisms were identified via MALDI-TOF MS between March 2014 and February 2016 formed the postintervention group. The patients whose microorganisms were identified by using conventional methods between March 2011 and February 2013 formed the preintervention group.

Results

The postintervention group (n=58) had a shorter mean time from blood draw to receiving the antimicrobial susceptibility results than the preintervention group (n=40) (90.2 ± 32.1 vs. 108.7 ± 43.1 h; p=0.02). The postintervention group was also more likely to have received active antimicrobial therapy by the time the susceptibility report became available (77% vs. 47%; p=0.005). Its 28-day mortality was also lower (40% vs. 70%; p=0.003). Univariate analysis showed that identification via MALDI-TOF MS (odds ratio, 0.28; 95% confidence interval, 0.12–0.66; p=0.004) and active therapy (odds ratio, 0.38; 95% confidence interval, 0.16–0.95; p=0.04) were associated with lower 28-day mortality.

Conclusion

Rapid microorganism identification via MALDI-TOF MS followed by appropriate antimicrobial therapy may improve the clinical outcomes of patients with sepsis.

Clinical and Microbiologic Characteristics of Early-onset Sepsis Among Very Low Birth Weight Infants: Opportunities for Antibiotic Stewardship

BACKGROUND

Most very low birth weight (VLBW, birth weight <1500 g) infants receive empiric antibiotics for risk of early-onset sepsis (EOS). The objective of this study was to determine the characteristics of VLBW infants with culture-confirmed EOS at a single center during 25 years and to identify opportunities for antibiotic stewardship.

METHODS

Retrospective cohort study includes VLBW infants admitted from 1990 to 2015. EOS was defined as isolation of a pathogen in blood or cerebrospinal fluid culture obtained at <72 hours of age. Clinical and microbiologic characteristics of EOS case infants were obtained by review of medical, laboratory and administrative records. Blood culture, antibiotic initiation and maternal discharge code data were available for all VLBW infants born between 1999 and 2013.

RESULT

One-hundred nine EOS cases (20.5/1000 VLBW births) occurred during the study period. Preterm labor, preterm rupture of membranes and/or the obstetrical diagnosis of chorioamnionitis were present in 106/109 cases (97%). Obligate anaerobic organisms accounted for 16% of cases. Time to culture positivity was 36 hours for 88% and 48 hours for 98% of cases. From 1999 to 2013, 97% of VLBW infants were evaluated for EOS and 90% administered empiric antibiotics; 22% of these infants were born by cesarean section to mothers with preeclampsia and without preterm labor or chorioamnionitis and had a 12-fold lower incidence of EOS compared with the remaining infants.

CONCLUSION

Decisions to initiate and discontinue empiric antibiotics among VLBW infants can be informed by the delivery characteristics of infected infants and by local microbiologic data.

Performance of two blood culture systems to detect anaerobic bacteria. Is there any difference?

We studied the performance characteristics of two blood culture (BC) bottles/systems, (i) BacT/ALERT-FN Plus/3D (bioMérieux, Marcy l'Étoile, France) and (ii) BACTEC-Lytic/9000 (Becton Dickinson, Sparks, USA) for detection of growth and time-to-positivity (TTP) against a balanced and diverse collection of anaerobic bacterial strains (n = 48) that included reference strains (n = 19) and clinical isolates (n = 29) of 32 species (15 Gram-negative and 17 Gram-positive). Standard suspension of bacteria was inoculated to each bottle in duplicates and incubated in the corresponding system. Overall, 62.5% (n = 30) of strains were detected by both BC bottle types. Comparing the two, 70.8% (n = 34) and 79.2% (n = 38) of strains were detected by BacT/ALERT-FN Plus and BACTEC-Lytic bottles, respectively (p = 0.38). Among Gram-negative anaerobes (n = 25) the detection rate was 76.0% (n = 19) vs. 92.0% (n = 23) (p = 0.22), respectively. Among Gram-positive anaerobes (n = 23) the detection rate was 65.2% (n = 15) in both bottles (p = 1). The average TTP per bottle was calculated only for the strains detected by both systems (n = 30) and was 40.85 h and 28.08 h for BacT/ALERT-FN Plus and BACTEC-Lytic, respectively (p < 0.001). The mean difference was 12.76 h (95% CI: 6.21-19-31 h). Six anaerobic strains were not detected by any system, including Gram-negative Porphyromonas gingivalis, and five Gram-positive strains: Finegoldia magna, Peptostreptococcus anaerobius, Propionibacterium acnes, Clostridium novyi and Clostridium clostridioforme. Furthermore, Eggerthella lenta and Prevotella bivia were detected only by BacT/ALERT-FN Plus, while Prevotella disiens and Prevotella intermedia were detected only by BACTEC-Lytic bottles. There were no major differences in detection rate among clinical and reference strains. Anaerobic bacteria represent a minority of BC isolates, however, far from ideal detection rate was observed in this study for both tested bottle/system combinations. Nevertheless, in those cases where both gave positive signal, BACTEC-Lytic was superior to BacT/ALERT FN Plus with 12.76 h shorter mean TTP. Improvements of media in blood culture bottles available for detection of anaerobes are warranted.

Selected Topics in Anaerobic Bacteriology

Alteration in the host microbiome at skin and mucosal surfaces plays a role in the function of the immune system, and may predispose immunocompromised patients to infection. Because obligate anaerobes are the predominant type of bacteria present in humans at skin and mucosal surfaces, immunocompromised patients are at increased risk for serious invasive infection due to anaerobes. Laboratory approaches to the diagnosis of anaerobe infections that occur due to pyogenic, polymicrobial, or toxin-producing organisms are described. The clinical interpretation and limitations of anaerobe recovery from specimens, anaerobe-identification procedures, and antibiotic-susceptibility testing are outlined. Bacteriotherapy following analysis of disruption of the host microbiome has been effective for treatment of refractory or recurrent Clostridium difficile infection, and may become feasible for other conditions in the future.

Low Utility of Pediatric Isolator Blood Culture System for Detection of Fungemia in Children: a 10-Year Review

The use of the Wampole Isolator 1.5-ml pediatric blood culture tube for the detection of fungemia in children was assessed by a 10-year retrospective review at two pediatric hospitals, The Hospital for Sick Children in Toronto, Canada, and the Children's Medical Center of Dallas, Texas. Over this period, a total of 9,442 pediatric Isolator specimens were processed, with yeast or yeast-like organisms recovered in 297 (3.1%) of the specimens (151 [1.6%] unique clinical episodes) and filamentous or dimorphic fungi recovered in 31 (0.3%) of the specimens (25 unique clinical episodes). Only 18 of the 151 clinical episodes of fungemia attributable to yeast were not detected by automated blood culture systems. The majority of isolated yeast were Candida spp., which were usually detected by automated systems, whereas the most common non-Candida yeast was Malassezia furfur, which the automated system failed to detect. Filamentous or dimorphic fungi were detected in 25 episodes, of which only 9 (36%) episodes were deemed clinically significant after chart review, indicating that in the majority of cases (16/25, 64%) fungal isolation represented contamination. In five of the nine clinically significant episodes, the isolated fungus (Histoplasma capsulatum, Coccidioides immitis/posadasii, Fusarium oxysporum, Aspergillus spp., and Bipolaris spp.) was also identified in other clinical specimens. Over the 10-year study period, the use of the pediatric Isolator system, at the discretion of the treating physician, only rarely provided useful clinical information for the diagnosis of fungemia in children, with the exception of M. furfur and possibly endemic mycoses.

Beyond Blood Culture and Gram Stain Analysis: A Review of Molecular Techniques for the Early Detection of Bacteremia in Surgical Patients

BACKGROUND

Sepsis from bacteremia occurs in 250,000 cases annually in the United States, has a mortality rate as high as 60%, and is associated with a poorer prognosis than localized infection. Because of these high figures, empiric antibiotic administration for patients with systemic inflammatory response syndrome (SIRS) and suspected infection is the second most common indication for antibiotic administration in intensive care units (ICU)s. However, overuse of empiric antibiotics contributes to the development of opportunistic infections, antibiotic resistance, and the increase in multi-drug-resistant bacterial strains. The current method of diagnosing and ruling out bacteremia is via blood culture (BC) and Gram stain (GS) analysis.

METHODS

Conventional and molecular methods for diagnosing bacteremia were reviewed and compared. The clinical implications, use, and current clinical trials of polymerase chain reaction (PCR)-based methods to detect bacterial pathogens in the blood stream were detailed.

RESULTS

BC/GS has several disadvantages. These include: some bacteria do not grow in culture media; others do not GS appropriately; and cultures can require up to 5 d to guide or discontinue antibiotic treatment. PCR-based methods can be potentially applied to detect rapidly, accurately, and directly microbes in human blood samples.

CONCLUSIONS

Compared with the conventional BC/GS, particular advantages to molecular methods (specifically, PCR-based methods) include faster results, leading to possible improved antibiotic stewardship when bacteremia is not present.

Performance of BacT/Alert resin-based FN plus bottles compared with BacT/Alert charcoal-based FN bottles for the detection of anaerobes in experimentally seeded blood cultures

Recently new resin-based BacT/Alert FAN Plus bottles containing antibiotic-binding polymeric beads, were introduced as an improvement of the charcoal-based FAN bottles for the recovery of bacteria and fungi. To assess the performance of the novel anaerobic FN plus bottles in the detection of anaerobic organisms, we compared the detection rate and the time to detection (TTD) in spiked resin-based FN Plus bottles and charcoal-based FN bottles. The bottles were experimentally seeded with reference strains or clinical strains collected from positive blood cultures. Five reference strains and fifty-five clinically significant anaerobic isolates were investigated, of which 91% (61/67) showed growth in both types of bottles within an incubation time of 5 days. A significant prolonged median TTD of 45 h for anaerobic microorganisms was observed in the resin-based bottles versus 29 h in the charcoal-based bottles (P < 0.0001). Bacteroides spp., associated with higher virulence and higher mortality rates in bloodstream infections, were detected faster in the charcoal-based bottles as compared to the resin-based bottles. In conclusion recently improved resin FN bottles showed a significantly increased median TTD for the recovery of anaerobic isolates.

Population-based epidemiology and microbiology of community-onset bloodstream infections

Bloodstream infection (BSI) is a major cause of infectious disease morbidity and mortality worldwide. While a positive blood culture is mandatory for establishment of the presence of a BSI, there are a number of determinants that must be considered for establishment of this entity. Community-onset BSIs are those that occur in outpatients or are first identified <48 h after admission to hospital, and they may be subclassified further as health care associated, when they occur in patients with significant prior health care exposure, or community associated, in other cases. The most common causes of community-onset BSI include Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae. Antimicrobial-resistant organisms, including methicillin-resistant Staphylococcus aureus and extended-spectrum β-lactamase/metallo-β-lactamase/carbapenemase-producing Enterobacteriaceae, have emerged as important etiologies of community-onset BSI.

Balancing Enthusiasm for Innovative Technologies with Optimizing Value: An Approach to Adopt New Laboratory Tests for Infectious Diseases Using Bloodstream Infections as Exemplar

A number of exciting new technologies have emerged to detect infectious diseases with greater accuracy and provide faster times to result in hopes of improving the provision of care and patient outcomes. However, the challenge in evaluating new methods lies not in the technical performance of tests but in (1) defining the specific advantages of new methods over the present gold standards in a practicable way and (2) understanding how advanced technologies will prompt changes in medical and public health decisions. With rising costs to deliver care, enthusiasm for innovative technologies should be balanced with a comprehensive understanding of clinical and laboratory ecosystems and how such factors influence the success or failure of test implementation. Selecting bloodstream infections as an exemplar, we provide a 6-step model for test adoption that will help clinicians and laboratorians better define the value of a new technology specific to their clinical practices.

Survey of physicians' perspectives and knowledge about diagnostic tests for bloodstream infections

Background

Physicians rely on blood culture to diagnose bloodstream infections (BSI) despite its limitations. As new technologies emerge for rapid BSI diagnosis, optimization of their application to patient care requires an understanding of clinicians’ perspectives on BSI diagnosis and how a rapid test would influence medical decisions.

Methods

We administered a 26-question survey to practitioners in infectious diseases/microbiology, critical care, internal medicine, and hematology/oncology services in USA and Germany about current standards in diagnosing and treating BSI and a hypothetical rapid BSI test.

Results

Responses from 242 providers had roughly equal representation across specialties. For suspected BSI patients, 78% of practitioners would administer empiric broad spectrum antibiotics although they estimated, on average, that 31% of patients received incorrect antibiotics while awaiting blood culture results. The ability of blood culture to rule in or rule out infection was very/extremely acceptable in 67% and 36%, respectively. Given rapid test results, 60–87% of practitioners would narrow the spectrum of antimicrobial therapy depending on the microorganism detected, with significantly higher percentages when resistance determinants were also tested. Over half of respondents felt a rapid test would be very/extremely influential on clinical practice.

Conclusions

Limitations of blood culture were perceived as a barrier to patient care. A rapid test to diagnose BSI would impact clinical practice, but the extent of impact may be limited by prevailing attitudes and practices. Opportunities exist for interventions to influence practitioners’ behaviors in BSI management particularly with emergence of newer diagnostic tests.

Performance of two resin-containing blood culture media in detection of bloodstream infections and in direct matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) broth assays for isolate identification: clinical comparison of the BacT/Alert Plus and Bactec Plus systems

We compared the clinical performances of the BacT/Alert Plus (bioMérieux) and Bactec Plus (Becton Dickinson) aerobic and anaerobic blood culture (BC) media with adsorbent polymeric beads. Patients ≥ 16 years old with suspected bloodstream infections (BSIs) were enrolled in intensive care units and infectious disease wards. A single 40-ml blood sample was collected from each and used to inoculate (10 ml/bottle) one set of BacT/Alert Plus cultures and one set of Bactec Plus cultures, each set consisting of one aerobic and one anaerobic bottle. Cultures were incubated ≤ 5 days in the BacT/Alert 3D and Bactec FX instruments, respectively. A total of 128 unique BSI episodes were identified based on the recovery of clinically significant growth in 212 aerobic cultures (106 BacT/Alert and 106 Bactec) and 151 anaerobic cultures (82 BacT/Alert and 69 Bactec). The BacT/Alert aerobic medium had higher recovery rates for Gram-positive cocci (P = 0.024), whereas the Bactec aerobic medium was superior for recovery of Gram-negative bacilli (P = 0.006). BacT/Alert anaerobic medium recovery rates exceeded those of the Bactec anaerobic medium for total organisms (P = 0.003), Gram-positive cocci (P = 0.013), and Escherichia coli (P = 0.030). In terms of capacity for diagnosing the 128 septic episodes, the BacT/Alert and Bactec sets were comparable, although the former sets diagnosed more BSIs caused by Gram-positive cocci (P = 0.008). They also allowed earlier identification of coagulase-negative staphylococcal growth (mean, 2.8 h; P = 0.003) and growth in samples from patients not on antimicrobial therapy that yielded positive results (mean, 1.3 h; P < 0.001). Similarly high percentages of microorganisms in BacT/Alert and Bactec cultures (93.8% and 93.3%, respectively) were identified by direct matrix-assisted laser desorption ionization-time of flight mass spectrometry assay of BC broths. The BacT/Alert Plus media line appears to be a reliable, timesaving tool for routine detection of BSIs in the population we studied, although further studies are needed to evaluate their performance in other settings.

Controlled clinical comparison of BacT/alert FA plus and FN plus blood culture media with BacT/alert FA and FN blood culture media

New blood culture media containing antibiotic-binding polymeric beads have been developed for the BacT/Alert (bioMérieux, Inc., Durham, NC) blood culture system. To assess the performance of these new media, we compared the new BacT/Alert aerobic medium (FA Plus) with resins to BacT/Alert FA medium with activated charcoal and the new BacT/Alert anaerobic medium (FN Plus) to BacT/Alert FN medium at 3 tertiary care medical centers. Study bottle pairs were inoculated with a target volume of 6 to 10 ml of blood from adults and incubated in the BacT/Alert 3D blood culture instrument. In the FA Plus versus FA comparison, there were 1,507 study pairs. Among 170 isolates causing true bloodstream infections (BSIs), significantly more Staphylococcus aureus (P<0.001) and total microorganisms (P<0.01) grew in the FA Plus bottle than in the FA bottle. Fewer coagulase-negative staphylococcal (CoNS) contaminants grew in the FA Plus bottle than in the FA bottle (10 versus 22; P=0.05). In addition, growth was detected earlier in the FA Plus bottle than in the FA bottle (P<0.001). In the FN Plus versus FN comparison, there were 2,386 study pairs. Among 201 isolates causing true BSIs, significantly more S. aureus (P<0.001), CoNS (P<0.005), and total microorganisms (P<0.001) grew in the FN Plus bottle than in the FN bottle. Also, significantly more CoNS contaminants grew in the FN Plus bottle than in the FN bottle (P<0.001). Overall, microorganisms were detected earlier in the FN Plus than in the FN bottle (P<0.001). Medical technologists at all 3 study sites preferred the new media for Gram stain interpretation. We conclude that the FA Plus and FN Plus media provide improved and earlier detection of microorganisms compared with the FA and FN media and are preferable for Gram stain interpretation as well.

Time to blood culture positivity as a predictor of clinical outcome in patients with Candida albicans bloodstream infection

Background

Few studies have assessed the time to blood culture positivity as a predictor of clinical outcome in fungal bloodstream infections (BSIs). The purpose of this study was to evaluate the time to positivity (TTP) of blood cultures in patients with Candida albicans BSIs and to assess its impact on clinical outcome.

Methods

A historical cohort study with 89 adults patients with C. albicans BSIs. TTP was defined as the time between the start of incubation and the time that the automated alert signal indicating growth in the culture bottle sounded.

Results

Patients with BSIs and TTPs of culture of ≤36 h (n=39) and >36 h (n=50) were compared. Septic shock occurred in 46.2% of patients with TTPs of ≤36 h and in 40.0% of patients with TTP of >36 h (p=0.56). A central venous catheter source was more common with a BSI TTP of ≤36 h (p=0.04). Univariate analyis revealed that APACHE II score≥20 at BSI onset, the development of at least one organ system failure (respiratory, cardiovascular, renal, hematologic, or hepatic), SOFA at BSI onset, SAPS II at BSI onset, and time to positivity were associated with death. By using logistic regression analysis, the only independent predictor of death was time to positivity (1.04; 95% CI, 1.0-1.1, p=0.035), with the chance of the patient with C. albicans BSI dying increasing 4.0% every hour prior to culture positivity.

Conclusion

A longer time to positivity was associated with a higher mortality for Candida albicans BSIs; therefore, initiating empiric treatment with antifungals may improve outcomes.

Superior sensitivity and decreased time to detection with the Bactec Peds Plus/F system compared to the BacT/Alert Pediatric FAN blood culture system

Here, we compare the sensitivities and times to detection (TTD) of BacT/Alert Pediatric FAN (PF) and Bactec Peds Plus blood culture bottles. Test bottles were inoculated with 2 ml of banked whole blood, 1-ml aliquots of antibiotic suspension, and organisms diluted to simulate a bacteremia level of 10 to 100 CFU/ml. The control bottles were inoculated with 3 ml of banked blood and organism suspensions only. The organism-drug combinations were Staphylococcus epidermidis and vancomycin, methicillin-resistant Staphylococcus aureus and vancomycin, Streptococcus pneumoniae, vancomycin, and ceftriaxone, Streptococcus agalactiae, ampicillin, and cefotaxime, Escherichia coli, cefotaxime, and cefepime, Pseudomonas aeruginosa, piperacillin-tazobactam, cefepime, and gentamicin, Neisseria meningitidis and ceftriaxone, and Haemophilus influenzae and ceftriaxone. The control and test bottle combinations were tested in duplicate. The bottles were incubated for 5 days; 32 control and 104 test bottles were incubated. Overall, the bacterial recovery rates for the PF and Peds Plus bottles were 37% and 62%, 94% and 100% in the controls, 19% and 50% in the test bottles, and 33% and 92% in the bottles with vancomycin, respectively. No bacteria were recovered from the bottles with S. pneumoniae, S. agalactiae, E. coli, N. meningitidis, or H. influenzae in combination with cefotaxime or ceftriaxone. The Peds Plus system detected P. aeruginosa in bottles with cefepime and piperacillin-tazobactam, but the PF system recovered bacteria only in bottles with trough levels of piperacillin-tazobactam. The mean TTD were shorter in the Peds Plus system controls (14.2 versus 18.0 h; P = 0.001) and the test bottles (14.3 versus 17.8 h; P = 0.008) than in the PF bottles. Overall, we demonstrated superior sensitivity, TTD, and antibiotic neutralization in the Bactec Peds Plus system compared to those in the Pediatric FAN system.

Rapid identification of bacterial and fungal pathogens from positive blood cultures by MALDI-TOF MS

Sepsis is a syndrome characterized by a systemic inflammatory response due to severe infection. Early detection of causal agents and appropriate antimicrobial treatment reduce mortality. Conventional microbiological methods often do not provide time critical results for an optimal early management. We used an in-house protocol based on Tween 80 to process 109 positive blood cultures for bacteria and yeast identification by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS), and results were compared to standard reference or automated methods. MALDI-TOF MS correctly identified 91.7% of the isolates. Correct identification was obtained for 57/62 (91.9%) aerobic/facultative anaerobic Gram-positive isolates, 53 (85.5%) at species level, and 4 (6.4%) at the genus level; 32/32 (100%) aerobic/facultative anaerobic Gram-negative isolates, 31 (96.9%) at species level, and 1 (3.1%) at the genus level; 7/7 (100%) obligate anaerobes, all at the genus level; 3/7 (42.8%) fungi, all at genus level. Overall, the median identification time of MALDI-TOF MS vs reference standard methods was significantly shorter: median (interquartile range) 7.1h (4.7-10.2) vs 48.1h (32.5-50.0), p<0.0001. MALDI-TOF MS is a valuable tool for rapid identification of pathogens in septic patients. An in-house protocol based on Tween 80 can be used to process positive blood cultures.

Update on blood cultures: how to obtain, process, report, and interpret

The detection and identification of microorganisms circulating in the bloodstream of patients is arguably one of the most important functions of the clinical microbiology laboratory. Effective implementation of this function requires careful consideration of specimen collection and processing, culture techniques, result reporting, and, perhaps most importantly, result interpretation by the physician. The purpose of this review is to provide a synopsis of the current state of the art for each of these areas, with the intention of providing adequate information to enable clinical laboratory personnel and physicians to critically evaluate and, if required, improve their current blood culture practices.

Comparison of 2 blood culture media shows significant differences in bacterial recovery for patients on antimicrobial therapy

BACKGROUND

Antimicrobial removal devices in blood culture media are designed to remove antibiotics from the blood culture solution, thereby facilitating bacterial growth. How well these devices function clinically has not been established.

METHODS

All blood drawn for culture from adult inpatients and emergency department visitors in a level I trauma center was placed in paired BACTEC Plus and BacT/Alert FAN culture media and studied simultaneously, consecutively, and prospectively between 1 February and 30 September 2011. All cultures were processed per standard laboratory protocols.

RESULTS

Of 9395 total cultures collected, 1219 (13%) were positive, 831 were included, and 524 (33%) contained pathogens. BACTEC had a 4.5-hour faster detection time (P < .0001), and isolated exclusively 182 of 524 (35%; P < .001) pathogens, 136 of 345 (39%) of the gram-positive cocci (P < .001), 48 of 175 (27%; P = .02) of the gram-negative rods, 101 of 195 (52%) of Staphylococcus aureus (P < .001), and 59 of 120 (49%; P = .004) septic events. If active antibiotics had been dosed 0-4 or 4-48 hours prior to culture collection, the odds of that culture growing in BACTEC were 4.8- and 5.2-fold greater, respectively, than of growing in BacT/Alert (P < .0001). Both were equivalent in the recovery of yeast and when no antimicrobials were dosed.

CONCLUSIONS

BACTEC media has faster time to detection and increased bacterial recovery over the BacT/Alert media in the following categories: overall growth, pathogens, septic events, gram-positive cocci, gram-negative rods, Staphylococcus aureus, and cultures where antimicrobials were dosed up to 48 hours before culture collection.

Evaluation of BACTEC Plus aerobic and anaerobic blood culture bottles and BacT/Alert FAN aerobic and anaerobic blood culture bottles for the detection of bacteremia in ICU patients

Blood culture is the most valuable laboratory test for the diagnosis of bacteremia and sepsis. The BACTEC FX and BacT/Alert 3D automated blood culture systems are commonly used in Korean health care facilities. A controlled clinical evaluation of the resin-containing BACTEC Plus aerobic (BA) and anaerobic (BN), and the charcoal-containing FAN aerobic (FA) and anaerobic (FN) bottles using blood from intensive care unit (ICU) patients was designed. The performances of these 2 systems with media containing particle absorbing antimicrobial agents were evaluated using the culture positivity rate and time to detection (TTD). TTD was collected using data management systems, either the Epicenter (BD Diagnostic Systems) or the hospital laboratory information system. A total of 1539 four-bottle sets were collected from 270 patients in medical and surgical ICUs. Blood culture samples included 1539 bottles each of BA, BN, FA, and FN, and yielded 113 (7.3%), 90 (5.8%), 104 (6.8%), and 80 (5.2%) positive bacterial or fungal isolates, respectively. There were significant differences between the resin-containing BA and BN samples in culture positivity and also between the charcoal-containing FA and FN samples, especially for Escherichia coli (25/27 versus 17/27, P < 0.05) and Acinetobacter baumannii (14/15 versus 7/15, P < 0.05). Significantly shorter recovery time was observed in BACTEC Plus aerobic bottles than in FAN aerobic bottles (17.2 and 24.7 h, respectively) (P < 0.001).

Diagnostic performance of a multiple real-time PCR assay in patients with suspected sepsis hospitalized in an internal medicine ward

Early identification of causative pathogen in sepsis patients is pivotal to improve clinical outcome. SeptiFast (SF), a commercially available system for molecular diagnosis of sepsis based on PCR, has been mostly used in patients hospitalized in hematology and intensive care units. We evaluated the diagnostic accuracy and clinical usefulness of SF, compared to blood culture (BC), in 391 patients with suspected sepsis, hospitalized in a department of internal medicine. A causative pathogen was identified in 85 patients (22%). Sixty pathogens were detected by SF and 57 by BC. No significant differences were found between the two methods in the rates of pathogen detection (P = 0.74), even after excluding 9 pathogens which were isolated by BC and were not included in the SF master list (P = 0.096). The combination of SF and BC significantly improved the diagnostic yield in comparison to BC alone (P < 0.001). Compared to BC, SF showed a significantly lower contamination rate (0 versus 19 cases; P < 0.001) with a higher specificity for pathogen identification (1.00, 95% confidence interval [CI] of 0.99 to 1.00, versus 0.94, 95% CI of 0.90 to 0.96; P = 0.005) and a higher positive predictive value (1.00, 95% CI of 1.00 to 0.92%, versus 0.75, 95% CI of 0.63 to 0.83; P = 0.005). In the subgroup of patients (n = 191) who had been receiving antibiotic treatment for ≥24 h, SF identified more pathogens (16 versus 6; P = 0.049) compared to BC. These results suggest that, in patients with suspected sepsis, hospitalized in an internal medicine ward, SF could be a highly valuable adjunct to conventional BC, particularly in patients under antibiotic treatment.

Comparison of BD Bactec Plus blood culture media to VersaTREK Redox blood culture media for detection of bacterial pathogens in simulated adult blood cultures containing therapeutic concentrations of antibiotics

Antibiotic neutralization in blood culture media from two automated systems was evaluated by measuring the recovery of organisms and times to detection in simulated cultures. Overall, BD Bactec Plus media (Bactec FX system) outperformed TREK 80 ml Redox media (VersaTREK system), although results suggest a relative rather than an absolute increased rate of recovery for the Bactec media.

Blood cultures: key elements for best practices and future directions

Bloodstream infections (BSI) cause significant morbidity and mortality among populations worldwide. Blood cultures (BCs) are regarded as the "gold standard" for diagnosis of bacteremia and are among the most important functions of the clinical microbiology laboratory. Significant changes in the methods and techniques of obtaining BCs have occurred since the first inception of BCs into clinical practice. Aside from significant improvements of established, conventional technology, new assays for diagnosis of bacteremia and fungemia, particularly those involving molecular techniques, are now available. BCs must be collected under sterile conditions and guidelines for appropriate collection, processing, and results reporting of BCs have been established. This review provides comprehensive information on optimal BC practices for laboratories, utilizing traditional approaches and emerging technology. As laboratories and clinicians must appreciate the key factors affecting the use of these techniques, improved communication between laboratory personnel and clinicians regarding such elements as duration of incubation, workup of contaminants and critical action value reporting will greatly improve the diagnostic approach to BSI.

Clinical impact of a commercially available multiplex PCR system for rapid detection of pathogens in patients with presumed sepsis

Background

Timely identification of pathogens is crucial to minimize mortality in patients with severe infections. Detection of bacterial and fungal pathogens in blood by nucleic acid amplification promises to yield results faster than blood cultures (BC). We analyzed the clinical impact of a commercially available multiplex PCR system in patients with suspected sepsis.

Methods

Blood samples from patients with presumed sepsis were cultured with the Bactec 9240™ system (Becton Dickinson, Heidelberg, Germany) and aliquots subjected to analysis with the LightCycler^® SeptiFast^® (SF) Test (Roche Diagnostics, Mannheim, Germany) at a tertiary care centre. For samples with PCR-detected pathogens, the actual impact on clinical management was determined by chart review. Furthermore a comparison between the time to a positive blood culture result and the SF result, based on a fictive assumption that it was done either on a once or twice daily basis, was made.

Results

Of 101 blood samples from 77 patients, 63 (62%) yielded concordant negative results, 14 (13%) concordant positive and 9 (9%) were BC positive only. In 14 (13%) samples pathogens were detected by SF only, resulting in adjustment of antibiotic therapy in 5 patients (7,7% of patients). In 3 samples a treatment adjustment would have been made earlier resulting in a total of 8 adjustments in all 101 samples (8%).

Conclusion

The addition of multiplex PCR to conventional blood cultures had a relevant impact on clinical management for a subset of patients with presumed sepsis.

Distribution, optimum detection time and antimicrobial susceptibility rates of the microorganisms isolated from blood cultures over a 4-year time period in a Turkish university hospital and a review of the international literature

This study retrospectively examined 8986 blood cultures from patients over a 4-year time period in an eastern Turkish university hospital to determine the detection times and distribution of isolated microorganisms using the automated BACTEC 9050 and BACTEC 9120 systems. A total of 1914 (21.3%) blood cultures contained pathogenic microorganisms and 252 (2.8%) positive cultures were considered contaminated. Of all the cultures, 18 (0.2%) were false positives and 224 (2.5%) were false negatives. In cultures containing pathogenic microorganisms, Gram-positive and Gram-negative bacterial isolation rates were 436 (22.8%) and 1440 (75.2%), respectively, and yeasts (all Candida sp.) were found in 38 (2.0%) cultures. Coagulase-negative staphylococci occurred in 936 (48.9%) cultures and Staphylococcus aureus occurred in 302 (15.8%) cultures. The mean detection time for all of the pathogens was 21 h and Brucella spp were isolated within 10 days. This study helps in understanding the epidemiology of the region and in providing positive therapeutic approaches. A review of the international literature helps to place this understanding into a global context.

Guidelines for evaluation of new fever in critically ill adult patients: 2008 update from the American College of Critical Care Medicine and the Infectious Diseases Society of America

OBJECTIVE

To update the practice parameters for the evaluation of adult patients who develop a new fever in the intensive care unit, for the purpose of guiding clinical practice.

PARTICIPANTS

A task force of 11 experts in the disciplines related to critical care medicine and infectious diseases was convened from the membership of the Society of Critical Care Medicine and the Infectious Diseases Society of America. Specialties represented included critical care medicine, surgery, internal medicine, infectious diseases, neurology, and laboratory medicine/microbiology.

EVIDENCE

The task force members provided personal experience and determined the published literature (MEDLINE articles, textbooks, etc.) from which consensus was obtained. Published literature was reviewed and classified into one of four categories, according to study design and scientific value.

CONSENSUS PROCESS

The task force met twice in person, several times by teleconference, and held multiple e-mail discussions during a 2-yr period to identify the pertinent literature and arrive at consensus recommendations. Consideration was given to the relationship between the weight of scientific evidence and the strength of the recommendation. Draft documents were composed and debated by the task force until consensus was reached by nominal group process.

CONCLUSIONS

The panel concluded that, because fever can have many infectious and noninfectious etiologies, a new fever in a patient in the intensive care unit should trigger a careful clinical assessment rather than automatic orders for laboratory and radiologic tests. A cost-conscious approach to obtaining cultures and imaging studies should be undertaken if indicated after a clinical evaluation. The goal of such an approach is to determine, in a directed manner, whether infection is present so that additional testing can be avoided and therapeutic decisions can be made.

Comparison of BACTEC PLUS blood culture media to BacT/Alert FA blood culture media for detection of bacterial pathogens in samples containing therapeutic levels of antibiotics

Blood culture bottles with antimicrobial removal systems are recommended for patients who develop fever while on antibiotics. This study compared the ability of Becton Dickinson (Sparks, MD) BACTEC PLUS bottles and bioMerieux (Durham, NC) BacT/Alert FA bottles to effectively remove vancomycin, cefoxitin, ceftriaxone, cefepime, piperacillin-tazobactam, ampicillin, oxacillin, gentamicin, and a combination of gentamicin/penicillin, thus allowing bacterial pathogens to grow. Each bottle was spiked with 10 ml of human blood, antibiotic, and strains of organisms susceptible to the antibiotic evaluated. The organisms used were type strains and clinical isolates of Staphylococcus aureus (methicillin susceptible and resistant), Streptococcus pneumoniae, a viridans streptococcus, Enterococcus faecalis, Enterococcus faecium, Streptococcus agalactiae, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Testing was completed in triplicate, using 10 to 100 CFU/ml of organisms with various concentrations of each antibiotic. Two rounds of testing were completed per antibiotic/organism combination. Bottles were mixed and loaded onto their respective instruments as per the manufacturer's instructions. Antimicrobial removal was evaluated on the basis of time to detection of organism growth, for up to 5 days of incubation. Overall, the BacT/Alert FA system recovered 25.1% of strains from test bottles and 96.9% of strains from growth control bottles (no antibiotic added), and the BACTEC PLUS system recovered 95.1% of strains from test bottles and 100% of strains from growth control bottles. Both systems performed well in the detection of Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa in the presence of gentamicin. In the presence of ceftriaxone, neither system was able to recover Streptococcus pneumoniae. The ability to remove vancomycin and cefoxitin was also determined by measuring antibiotic levels remaining in bottles after 1 h of incubation. The results demonstrated remaining levels of 72 to 90% of vancomycin and 71 to 72% of cefoxitin in the BacT/Alert system. For the BACTEC system, remaining levels were 0 to 30% of vancomycin and 0% of cefoxitin. Under these simulated conditions, the BACTEC PLUS system was superior to the BacT/Alert FA system in recovering gram-positive and gram-negative bacterial pathogens in the presence of beta-lactam antibiotics, gentamicin/penicillin, and vancomycin.

Time to positivity in blood cultures of adults with Streptococcus pneumoniae bacteremia

BACKGROUND

previous studies have established that bacterial blood concentration is related with clinical outcome. Time to positivity of blood cultures (TTP) has relationship with bacterial blood concentration and could be related with prognosis. As there is scarce information about the usefulness of TTP, we study the relationship of TTP with clinical parameters in patients with Streptococcus pneumoniae bacteremia.

METHODS

TTP of all cases of Streptococcus pneumoniae bacteremia, detected between January 1995 and December 2004 using the BacT/Alert automated blood culture system in a teaching community hospital was analyzed. When multiple cultures were positive only the shortest TTP was selected for the analysis.

RESULTS

in the study period 105 patients with Streptococcus pneumoniae bacteremia were detected. Median TTP was 14.1 hours (range 1.2 h to 127 h). Immunosuppressed patients (n = 5), patients with confusion (n = 19), severe sepsis or shock at the time of blood culture extraction (n = 12), those with a diagnosis of meningitis (n = 7) and those admitted to the ICU (n = 14) had lower TTP. Patients with TTP in the first quartile were more frequently hospitalized, admitted to the ICU, had meningitis, a non-pneumonic origin of the bacteremia, and a higher number of positive blood cultures than patients with TTP in the fourth quartile. None of the patients with TTP in the 90th decile had any of these factors associated with shorter TTP, and eight out of ten patients with TTP in the 10th decile had at least one of these factors. The number of positive blood cultures had an inverse correlation with TTP, suggesting a relationship of TTP with bacterial blood concentration.

CONCLUSION

Our data support the relationship of TTP with several clinical parameters in patients with Streptococcus pneumoniae bacteremia, and its potential usefulness as a surrogate marker of outcome.

Evaluation of blood culture bottles seeded with X-V factors for the detection of Neisseria meningitidis and Haemophilus influenzae

The purpose of this in vitro study was to determine the ability of seeded and not-seeded commercial pediatric blood culture bottles to support the growth of the most frequently responsible microorganisms for bacterial meningitides (Neisseria meningitidis, and Haemophilus influenzae). Tests have been carried out with an automated colorimetric pediatric blood culture system, BacTAlert, Organon Teknika. Bottles were inoculated with X-V factors and serial dilutions of the each bacterium in six times (10(1)-10(6) colony forming unit [CFU]/ml). The bottles, which were supplemented with X-V factors, proved to be effective and time to detection (TTD) was shorter than the un-seeded bottles (p0.05). Time difference between seeded and not-seeded bottles was getting greater at high dilutions of both bacteria. We consider that in presence of a few bacteria, the seeding of bottles with X-V factors is very critical obtaining N. meningitidis, and H. influenzae as the causative agents of meningitidis. The recovery rate of the microorganisms, which were isolated from cerebrospinal fluid by using the X-V factor-seeded blood culture bottles, is therefore higher than with the conventional culture methods.

Diagnosis of infection in sepsis: An evidence-based review

OBJECTIVE

In 2003, critical care and infectious disease experts representing 11 international organizations developed management guidelines for the diagnosis of infection in sepsis that would be of practical use for the bedside clinician, under the auspices of the Surviving Sepsis Campaign, an international effort to increase awareness and improve outcome in severe sepsis.

DESIGN

The process included a modified Delphi method, a consensus conference, several subsequent smaller meetings of subgroups and key individuals, teleconferences, and electronic-based discussion among subgroups and among the entire committee.

METHODS

The modified Delphi methodology used for grading recommendations built on a 2001 publication sponsored by the International Sepsis Forum. We undertook a systematic review of the literature graded along five levels to create recommendation grades from A to E, with A being the highest grade. Pediatric considerations to contrast adult and pediatric management are in the article by Parker et al. on p. S591.

CONCLUSIONS

Obtaining a precise bacteriological diagnosis before starting antibiotic therapy is, when possible, of paramount importance for the success of therapeutic strategy during sepsis. Two to three blood cultures should be performed, preferably from a peripheral vein, without interval between samples to avoid delaying therapy. A quantitative approach is preferred in most cases when possible, in particular for catheter-related infections and ventilator-associated pneumonia. Diagnosing community-acquired pneumonia is complex, and a diagnostic algorithm is proposed. Appropriate samples are indicated during soft tissue and intraabdominal infections, but cultures obtained through the drains are discouraged.

Early detection and identification of commonly encountered Candida species from simulated blood cultures by using a real-time PCR-based assay

In a recent study, Candida species in clinical blood samples were detected using a real-time PCR-based method (Maaroufi et al, J Clin Microbiol 2003, 41:3293-3298). For the present study, we evaluated the efficiency of this method as an adjunct to the BACTEC blood culture system to early detection of positivity and negativity of simulated low candidemias. We first established an in vitro correlation between the inoculum of the most frequently encountered Candida species and the time to positivity of these microorganisms. Then, aliquots from blood culture bottles infected with a final average candidal inoculum of 3.18 colony-forming units (CFU)/culture bottle (range, 1 to 6 CFU) were collected at increasing incubation times, and DNA was extracted and submitted to the TaqMan-based PCR assay. To optimize this assay, we evaluated the effect of adding 0.5% bovine serum albumin (BSA) to DNA extracts and found that it decreased the effects of inhibitors. Using specific probes for the tested Candida species, the PCR assay was positive on blood culture aliquots collected from the BACTEC system after a minimum culture turnaround time (TAT) of 3.11 +/- 1.24 hours. Addition of BSA to PCR reaction mixtures improves the TAT (1.84 +/- 0.41 hours). Hence, the combination of DNA "amplification" in the culture bottles by normal growth with an additional DNA amplification by PCR might be a reliable tool facilitating the early diagnosis of low candidemias.

Comparison of Mycosis IC/F and plus Aerobic/F media for diagnosis of fungemia by the bactec 9240 system

Fungemia is associated with a high mortality rate. We compared the performance of the Mycosis IC/F selective fungal medium and the Plus Aerobic/F standard bacteriological medium for the diagnosis of fungemia on the Bactec 9240 automatic system. We retrospectively analyzed 550 blood culture pairs composed of one Mycosis IC/F vial and one Plus Aerobic/F vial, drawn in 187 patients with fungemia. The positivity rate by vial was significantly higher on Mycosis IC/F medium than on Plus Aerobic/F medium (88.0% versus 74.9%, P < 0.0001). The positivity rate for fungus detection on Plus Aerobic/F medium fell to 26.9% when bacteria were present in the same vial. The positivity rate by patient was also significantly higher on Mycosis IC/F medium than on Plus Aerobic/F medium (92.5% versus 75.9%, P < 0.0001). A marked superiority of Mycosis IC/F medium was demonstrated for diagnosis of Candida glabrata fungemia (31 of 31, 100%, versus 18 of 31, 58.1%, P < 0.0001). The mean detection time was significantly shorter on Mycosis IC/F medium than on Plus Aerobic/F medium (28.9 +/- 22.2 h versus 36.5 +/- 24.6 h, P < 0.0001). The mean time saving was 8.8 h for Candida albicans and 43.7 h for C. glabrata. Mycosis IC/F medium enabled more sensitive and earlier diagnosis, particularly for the two strains most frequently responsible for fungemia, C. albicans and C. glabrata, and also in the event of the concomitant presence of both yeasts and bacteria. In patients with risk factors, it would thus appear to be sensible to draw a Mycosis IC/F vial in addition to the standard bacteriological vials.

Direct comparison of the BACTEC 9240 and BacT/ALERT 3D automated blood culture systems for candida growth detection

A direct comparison of two automated blood culture systems was conducted to compare their ability to detect Candida growth. The systems evaluated were the BACTEC 9240 (Bactec) and BacT/ALERT 3D (BacT). The aerobic, anaerobic, and mycology media for each system were evaluated: Bactec Plus Aerobic/F, Plus Anaerobic/F, and Myco/F Lytic bottles, respectively, and BacT FA, SN, and MB bottles, respectively. Each blood culture bottle was inoculated with fresh blood from healthy donors. Fifty isolates of Candida spp. were used. The six different blood culture bottles were each inoculated with 1000 yeasts per bottle and then incubated in the corresponding automated system. The BacT detected growth of 90% (135 of 150) of Candida pathogens, while Bactec detected 66% (100 of 150). Growth was detected in all BacT and Bactec mycology bottles, all BacT aerobic bottles, and by terminal subculture of all bottles. Sixty-five of 300 (22%) bottles had no growth detected; 50 from the Bactec (5 aerobic and 45 anaerobic) and 15 from the BacT (all anaerobic). Terminal subculture of "negative" bottles demonstrated viable yeast growth from all 65 bottles, representing 65 false-negatives. The mean time to growth detection in the BacT system was 25.62 h while the Bactec was 27.30 h (P < 0.01). Both automated blood culture systems detected all episodes of simulated candidemia when specialized mycology media were used. However, when only standard aerobic and anaerobic media were used, the BacT performed better than the Bactec in overall growth detection, time to growth detection, and number of false-negatives.

Detection of simulated candidemia by the BACTEC 9240 system with plus aerobic/F and anaerobic/F blood culture bottles

We studied the ability of the BACTEC 9240 automated blood culture system to detect simulated candidemia, including both Candida albicans and non-albicans Candida species. Simulated blood cultures were produced using 50 Candida isolates and BACTEC Plus Aerobic/F and Anaerobic/F blood culture bottles. Ten milliliters of blood and a suspension of each isolate containing 1,000 CFU were introduced into each bottle and then incubated at 35 degrees C in the BACTEC 9240 system. The system detected growth in 56 of 100 bottles. Four isolates did not have growth detected in either bottle after 21 days of incubation, resulting in four missed episodes of candidemia. If the blood culture bottles had been incubated for 5 days, an additional episode of candidemia would have remained undetected. If the bottles had been incubated for only 3 days, another episode would have been missed, resulting in up to six missed episodes of candidemia (four Candida glabrata isolates, one C. albicans isolate, and one Candida rugosa isolate). Terminal subculture of bottles without detected growth recovered yeast in 93% (41 of 44) of the bottles, representing 41 false negatives. In bottles where growth was detected, the time to detection was approximately 24 h. However, the mean time to growth detection for C. glabrata isolates in anaerobic medium was 22.14 +/- 2.47 h, but it was 120.89 +/- 35.33 h in aerobic medium (P < 0.001). The BACTEC 9240 system detected growth of most Candida isolates; however, the delayed time to detection of C. glabrata is clinically significant. Given the high rate of false negatives, terminal subcultures may be helpful in certain situations.

Bacterial contamination of ex vivo processed PBPC products under clean room conditions

BACKGROUND

Patients undergoing high-dose radio- and/or chemotherapy and autologous or allogeneic PBPC transplantation are at high risk for infections owing to profound immunosuppression. In this study, the rate of microbial contamination of ex vivo processed PBPC products was analyzed, comparing preparation under clean room conditions to standard laboratory conditions.

STUDY DESIGN AND METHODS

After implementation of good manufacturing practice conditions in the two participating institutions, the microbial contamination rate of 366 PBPC harvests from 198 patients was determined under certified clean room conditions (Group A) from 2000 until 2002. To investigate influence of improved environmental conditions along with other parameters, this set of samples was compared with a historical control set of 1413 PBPC products, which have been processed ex vivo under a clean bench in a regular laboratory room and were harvested from 626 patients (Group B) from 1989 until 2000.

RESULTS

In Group B microbial contamination was found in 74 PBPC products (5.2%) from 57 patients. In Group A microbial growth was detected in 3 leukapheresis products (0.8%) from 3 patients. After exclusion of PBPC products, which were probably contaminated before manipulation, statistical analysis showed a significant difference (chi2= 10.339; p < 0.001).

CONCLUSION

These data suggest an impact of clean room conditions on the bacterial contamination rate of PBPC products. To identify confounding variables, variables like technique of leukapheresis, culture methodology, and microbial colonization of central venous catheters were taken into account. Further variables might be identified in following studies.

Evaluation of BACTEC MYCO/F Lytic medium for recovery of mycobacteria, fungi, and bacteria from blood

MYCO/F Lytic medium (MFL), a liquid medium developed for use with the BACTEC 9240 blood culture system, was compared to the Isolator system (IS) for the recovery of fungi and to the BACTEC 13A medium for the recovery of mycobacteria. Recovery of bacteria was compared to routine BACTEC Plus Aerobic/F (AF) blood cultures. Microbial growth was detected in 203 (17%) of 1,166 blood cultures. Fifty-seven specimens were positive for fungi: 35 were positive with both IS and MFL; six were positive with IS only (three Candida albicans, one Histoplasma capsulatum, one Candida glabrata, and one Fusarium species isolate); three were positive with AF only (two C. albicans and one Candida parapsilosis isolate); and 13 were positive with MFL only (five C. glabrata, three C. albicans, two Candida krusei, two Candida tropicalis, and one C. parapsilosis isolate; P > 0.05 versus IS). Eighteen of 19 blood cultures positive for H. capsulatum grew in both IS and MFL, although the time to detection for MFL was greater. The mean time to detection for all fungi was 8.15 days for IS and 12.07 days for MFL. Seven hundred forty specimens were also cultured for mycobacteria with MFL and 13A. Forty-four grew mycobacteria; 38 were positive with both 13A and MFL; and 16 were positive with MFL only. Mycobacterium avium was recovered from 41 specimens; 36 were positive for both systems and 5 were positive for MFL alone. MFL was also compared to the AF bottle for the same 740 specimens. MFL and AF both detected 34 of the 40 clinically significant bacteria, while IS detected only 15 of 40. In summary, MFL is an excellent medium for the recovery of fungi, mycobacteria, and bacteria; however, the time to detection of H. capsulatum is increased.

Controlled clinical comparison of BACTEC plus anaerobic/F to standard anaerobic/F as the anaerobic companion bottle to plus aerobic/F medium for culturing blood from adults

To determine the optimal anaerobic companion bottle to pair with BACTEC Plus Aerobic/F medium for recovery of pathogenic microorganisms from adult patients with bacteremia and fungemia, we compared Plus Anaerobic/F bottles with Standard Anaerobic/F bottles, each of which was filled with 4 to 6 ml of blood. The two bottles were paired with a Plus Aerobic/F bottle filled with 8 to 12 ml of blood. A total of 14,011 blood culture sets were obtained. Of these, 11,583 sets were received with all three bottles filled adequately and 12,257 were received with both anaerobic bottles filled adequately. Of 818 clinically important isolates detected in one or both adequately filled anaerobic bottles, significantly more staphylococci (P < 0.001), streptococci (P < 0.005), Escherichia coli isolates (P < 0.02), Klebsiella pneumoniae isolates (P < 0.005), and all microorganisms combined (P < 0.001) were detected in Plus Anaerobic/F bottles. In contrast, significantly more anaerobic gram-negative bacilli were detected in Standard Anaerobic/F bottles (P < 0.05). Of 397 unimicrobial episodes of septicemia, 354 were detected with both pairs, 30 were detected with Plus Aerobic/F-Plus Anaerobic/F pairs only, and 13 were detected with Plus Aerobic/F-Standard Anaerobic/F pairs only (P < 0.05). Significantly more episodes of bacteremia caused by members of the family Enterobacteriaceae (P < 0.05) and aerobic and facultative gram-positive bacteria (P < 0.025) were detected with Plus Anaerobic/F bottles only. In a paired-bottle analysis, 810 of 950 isolates were recovered from both pairs, 90 were recovered from Plus Aerobic/F-Plus Anaerobic/F pairs only, and 50 were recovered from Plus Aerobic/F-Standard Anaerobic/F pairs only (P < 0.001). Paired Plus Aerobic/F-Plus Anaerobic/F bottles yielded significantly more staphylococci (P < 0.001), streptococci (P < 0.05), and members of the family Enterobacteriaceae (P <0.001). We conclude that Plus Anaerobic/F bottles detect more microorganisms and episodes of bacteremia and fungemia than Standard Anaerobic/F bottles as companion bottles to Plus Aerobic/F bottles in the BACTEC 9240 blood culture system.

Controlled comparison of BacT/ALERT FAN aerobic medium and BATEC fungal blood culture medium for detection of fungemia

Yeasts are an increasingly common cause of nosocomial bloodstream infections. Methods for their detection are many; controlled comparisons are few. The vented FAN aerobic blood culture medium has been shown to be superior to the standard BacT/ALERT aerobic medium for the detection of fungemia as well as bacteremia. The BACTEC selective fungal medium (FM) (BD Biosciences, Sparks, Md.) allowed detection of more episodes of fungemia than did a resin-containing medium with equal volumes of blood cultured. Therefore, we compared vented FAN to FM for the ability to recover fungi from the blood of patients who were at increased risk of having fungemia. From 5,109 cultures processed for which both FAN and FM bottles were adequately filled, fungi were recovered from 87 cultures. Of these, 47 were detected with both bottles, 12 were detected with FAN only, and 28 were detected with FM only (P < 0.05). FAN was the first bottle positive for 36 of the 47 cultures for which both bottles yielded the same fungus, whereas the FM bottle was the first bottle positive for 11 cultures (P < 0.001). A total of 54 episodes of fungemia were identified, with 40 detected by both media, 4 detected only by FAN, and 10 detected only by FM (P value, not significant). We conclude that the vented FAN aerobic bottle is comparable to the FM bottle for detection of episodes of yeast infection but has the added benefit of detecting bacteria.

Effectiveness of resins in neutralizing antibiotic activities in bactec plus Aerobic/F culture medium

Incorporating resins in blood culture media can effectively reduce the activities of several antibiotics. It was shown that the activities of some generally used antibiotics decreased by 80 to 90% within 2 h in Bactec Plus Aerobic/F resin-containing culture medium. Bactec vials containing resins were still found to be positive for bacteria when antibiotics were present. The addition of beta-lactamase shortened the detection time irrespective of the presence of resins.

Controlled comparative evaluation of BacT/Alert FAN and ESP 80A aerobic media as means for detecting bacteremia and fungemia

During a one-year period, a total of 6,305 blood cultures were processed in a tertiary-care teaching hospital; 6 to 12 ml of blood was inoculated into both a BacT/Alert Fan aerobic bottle and an ESP 80A aerobic bottle. The FAN aerobic bottle contains an antimicrobial-absorbing material; the 80A aerobic bottle does not. Bottles were processed on their respective continuous-monitoring blood culture instruments for up to five days of incubation. Four hundred thirty-three cultures (6.9%) representing 301 septic episodes in 235 different patients yielded 490 bacteria or yeasts thought to be clinically significant. Two hundred seventy-five of the 433 presumed clinically significant positive cultures (63.5%) representing 195 septic episodes and yielding 301 isolates were positive in both FAN and 80A bottles. One hundred nine significant positive cultures (25.2%) (i.e., cultures positive with an organism judged to be of probable clinical significance) from 70 septic episodes yielded 126 isolates only in FAN bottles. Conversely, the 80A bottle was exclusively positive in 49 instances (11.3%), representing 36 septic episodes and yielding 63 isolates. The higher rates of significant positive blood cultures, numbers of septic episodes documented, and numbers of isolates recovered in FAN bottles versus 80A bottles were all statistically significant (P < 0.05). Enhanced rates of detection of presumed clinically significant isolates in FAN bottles were largely accounted for by Staphylococcus aureus, members of the Enterobacteriaceae, and non-Pseudomonas aeruginosa miscellaneous gram-negative bacilli from patients receiving antimicrobial therapy at the time blood cultures were obtained. Enhanced recovery of one organism group, the beta-hemolytic streptococci, occurred in 80A. With one exception, detection times were essentially equivalent in the two systems. The single exception pertained to streptococci and enterococci, which were recovered significantly faster in 80A bottles. Three hundred thirty-eight of the 6,305 blood cultures evaluated in this study (5.4%) were judged likely to be contaminated. The percentages of probable contaminated cultures were as follows: 26.6% FAN and 80A; 42.3% FAN only; 31.1% 80A only (P < 0.05). Finally, the instrument false-positive rates for the two systems were 0.7% with FAN and 3.0% with 80A (P < 0.05). We conclude that while contamination rates were slightly higher with FAN than with 80A, use of FAN aerobic bottles in conjunction with the BacT/Alert system will yield significantly higher numbers of clinically significant blood culture isolates than 80A bottles and the ESP system. Furthermore, this enhanced detection is most conspicuous in patients receiving antimicrobial therapy at the time blood cultures are performed, probably due to the presence of an antimicrobial-absorbing material in FAN aerobic bottles.