Automated Blood Culture Systems

New Microbiological Techniques for the Diagnosis of Bacterial Infections and Sepsis in ICU Including Point of Care

Purpose of Review

The aim of this article is to review current and emerging microbiological techniques that support the rapid diagnosis of bacterial infections in critically ill patients, including their performance, strengths and pitfalls, as well as available data evaluating their clinical impact.

Recent Findings

Bacterial infections and sepsis are responsible for significant morbidity and mortality in patients admitted to the intensive care unit and their management is further complicated by the increase in the global burden of antimicrobial resistance. In this setting, new diagnostic methods able to overcome the limits of traditional microbiology in terms of turn-around time and accuracy are highly warranted. We discuss the following broad themes: optimisation of existing culture-based methodologies, rapid antigen detection, nucleic acid detection (including multiplex PCR assays and microarrays), sepsis biomarkers, novel methods of pathogen detection (e.g. T2 magnetic resonance) and susceptibility testing (e.g. morphokinetic cellular analysis) and the application of direct metagenomics on clinical samples. The assessment of the host response through new “omics” technologies might also aid in early diagnosis of infections, as well as define non-infectious inflammatory states.

Summary

Despite being a promising field, there is still scarce evidence about the real-life impact of these assays on patient management. A common finding of available studies is that the performance of rapid diagnostic strategies highly depends on whether they are integrated within active antimicrobial stewardship programs. Assessing the impact of these emerging diagnostic methods through patient-centred clinical outcomes is a complex challenge for which large and well-designed studies are awaited.

Collection, transport and storage procedures for blood culture specimens in adult patients: recommendations from a board of Italian experts

Bloodstream infections (BSIs) remain a potentially life-threatening condition. The gold standard for the diagnosis of BSI is still blood cultures (BCs), and the diagnostic yield depends on clinical and technical factors that have an impact on collection and transportation. Hence, monitoring of the entire pre-analytical process from blood collection to transportation to the microbiology laboratory is critical. To optimize the clinical impact of the diagnostic and therapeutic procedures, a multidisciplinary approach and univocal protocols are mandatory. A board of specialists discussed the available evidence on the pre-analytical process and produced the present document to guide physicians and nurses on the ideal execution of BC: (1) timing and preparation for blood collection; (2) skin antisepsis; (3) blood volume; (4) sampling method and safety; (5) medium to be used; (6) time to BC transportation; and (7) quality assurance and quality management.

Central line bundle including split-septum device and single-use prefilled flushing syringes to prevent port-associated bloodstream infections: a cost and resource-utilization analysis

Background

Central line bundle programs were found to be effective in decreasing central line-associated bloodstream infection rates in pediatric cancer patients with ports. However, cost-effectiveness studies of central line bundle programs in pediatric cancer patients are limited, and most available data are from intensive care unit or adult studies.

Methods

In this cross-sectional study spanning 6 years, comprehensive assessment of total health care costs attributable to CLABSI’s associated with ports between two periods.

Results

This cross-sectional study was carried out in the pediatric hematology-oncology ward of Dr. Behçet Uz Children’s Hospital from 1 August November 2011 to 31 July 2017. The CLABSI rates decreased significantly from 8.31 CLABSIs to 3.04 per 1000 central line days (p < 0.001). In the pre-bundle period, total attributable costs spent for of patients with CLABSI were $130,661, and in the bundle period, total attributable costs spent for patients with CLABSI were $116,579. Within bundle implantation, 71 potential CLABSI were prevented, which saved an additional $208,977.

Conclusion

Our study shows that central line bundles decreases not only the CLABSI rate but also decreases attributable costs due to CLABSI. Expenses spent for bundle elements, were covered by savings by preventing CLABSI with higher costs.

Infections in Pediatric Burn Patients: An Analysis of One Hundred Eighty-One Patients

Background: Infectious complications are one of the most life-threatening complications and result in substantial mortality and morbidity in children who have been burned. The goal of the study is to assess the risk factors for sepsis in pediatric burn patients in a referral hospital. Methods: This study was performed at the Pediatric Burn Unit of Ankara Child Health and Diseases Hematology Oncology Training and Research Hospital during the period between January 2014 and June 2017. The patients were evaluated for age, sex, burn etiology, burned body surface area (BSA), the presence of inhalation injury, sepsis, positive cultures, the micro-organisms cultured samples, and septic focus. Results: A total of 181 patients were included in the study. The most common cause of burns was scalds in 120 patients (66.3%). Forty-one patients (22.7%) developed health-care-associated infection and sepsis. Gram-negative micro-organisms were isolated in 40 (97.6%) patients (Acinetobacter spp., Pseudomonas aeruginosa, Klebsiella pneumonia) with sepsis. Carbapenem resistance was detected in 31 (93.8%) of 40 patients. Mortality was observed in 11 patients (6.1%) in the group with sepsis. Burn surface area, burn depth, C-reactive protein (CRP) values, mortality, Garcés index, and Baux index were higher in the group with sepsis (p < 0.05). Multiple regression analysis revealed that mechanism of injury (flame), burned BSA ≥25%, C-reactive protein ≥6 mg/dL (area under the curve [AUC]: 0.76 p < 0.001 and AUC: 0.90, p < 0.001, respectively) at admission were independent parameters for development of sepsis in pediatric burn patients. Conclusion: Multi-drug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii were important agents of blood stream infection in burned children. Burned BSA ≥25% and CRP ≥6 mg/dL were risk factors for developing sepsis in pediatric burn patients.

New Microbiological Techniques in the Diagnosis of Bloodstream Infections

BACKGROUND

When a bloodstream infection is suspected, the preliminary and definitive results of culture-based microbiological testing arrive too late to have any influence on the initial choice of empirical antibiotic treatment.

METHODS

This review is based on pertinent publications retrieved by a selective search of the literature and on the authors' clinical and scientific experience.

RESULTS

A number of technical advances now enable more rapid microbiological diagnosis of bloodstream infections. DNA- based techniques for the direct detection of pathogenic organisms in whole blood have not yet become established in routine use because of various limitations. On the other hand, matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS) has become available for routine use in clinical laboratories and has markedly shortened the time to diagnosis after blood samples that have been cultured in automated blood-culture systems turn positive. Further developments of this technique now enable it to be used directly for blood cultures that have been flagged positive, as well as for subcultures that have been incubated for only a short time on a solid nutrient medium. The microbial biomass of the subculture can also be used in parallel for more rapid susceptibility testing with conventional methods, or, in future, with MALDI-TOF MS.

CONCLUSION

The potential of all of these new techniques will only be realizable in practice if they are optimally embedded in the diagnostic process and if sufficient attention is paid to pre-analytical issues, particularly storage and transport times.

Impact of central line bundle for prevention of umbilical catheter-related bloodstream infections in a neonatal intensive care unit: A pre-post intervention study

BACKGROUND

Central line-associated bloodstream infection is the most common infection associated with healthcare in preterm infants. The purpose of this 18-month cross-sectional study was to evaluate the effectiveness of bundle applications in the prevention of umbilical venous catheter (UVC)-associated bloodstream infections.

METHODS

This study included patients in whom UVCs were inserted and who were diagnosed with central line-associated bloodstream infection between July 1, 2016, and December 31, 2017, according to the Centers for Disease Control and Prevention criteria. During the second 9-month period of the study (April 1, 2017, to December 31, 2017), bundles were implemented.

RESULTS

In the prebundle period, 589 patients were admitted to the neonatal intensive care unit, and 6,769 hospitalization days and 485 UVC days were recorded. Similarly, during the bundle period, 508 patients were admitted to the neonatal intensive care unit, and 7,789 hospitalization days and 508 UVC days were recorded. The UVC-associated bloodstream infection rate was 12.4 per 1,000 catheter days in the prebundle period and decreased to 3.9 per 1,000 catheter days in the bundle period. Thus, after introducing bundle applications, the rate of infection decreased by 68% (P < .01).

CONCLUSIONS

This study showed that bundle application effectively reduced UVC-associated bloodstream infection.

Central line bundle for prevention of central line-associated bloodstream infection for totally implantable venous access devices (ports) in pediatric cancer patients

OBJECTIVE

The clinical impact of central line bundle programs for central line-associated bloodstream infections has been well demonstrated in intensive care units. However, the experience of central line bundle programs in totally implantable venous access devices (ports) in pediatric-hematology patients was limited.

METHODS

A retrospective study was designed to compare and evaluate the clinical impact of implementing a central line bundle for a 2-year 5-month period, including 10 months of prebundle period, 11 months of central line bundle (that includes needleless split-septum devices), and finally 8 months of central line bundle period in which single-use prefilled flushing devices were added to the previous central line bundle.

RESULTS

During the prebundle period, the rate of 14.5 central line-associated bloodstream infections per 1000 CL-days had decreased to 5.49 CLABSIs per 1000 CL-days in the first bundle period. The incidence rate ratio with these two groups was 0.379, indicating a relative risk reduction of 62% ( p = 0.005). By the addition of single-use prefilled flushing devices to the first bundle program, the central line-associated bloodstream infection rate decreased to 2.63 per 1000 CL-days. Port removal rate due to central line-associated bloodstream infections was 0.46 per 1000 catheter days in the bundle period, which was significantly lower than in the prebundle period in which port removal rate was 4.5 per 1000 catheter days ( p < 0.001).

CONCLUSION

Central line bundle programs were found to be effective in decreasing central line-associated bloodstream infection rates, improving patients' quality of life by preventing ports removal due in pediatric cancer patients.

Utility of Acridine Orange staining for detection of bacteria from positive blood cultures

The diagnostic performance of AO stain was evaluated for the detection of bacteria and or fungi from positive blood cultures. The sensitivity of Gram stain (GS) was 98.26% while Acridine Orange (AO) stain proved to be more sensitive (100%) with a Positive and Negative Predictive Value of 100% each. The specificity of both the stains was 100%. Overall agreement between the two stains was 98.23% (688/700). The organisms that were missed by GS and positive by AO were Candida species (Sutton, 2006) and Gram negative bacilli (GNB) (Sutton, 2006). Sensitivity of GS was 82.35% and AO was 100% among mixed cultures. Immediate reporting of the results of AO stain would have a significant impact on clinical management of patients with serious blood stream infections.

Burn-associated bloodstream infections in pediatric burn patients: Time distribution of etiologic agents

BACKGROUND

Infections are the leading cause of morbidity and mortality in patients with burns in burn units. Bloodstream infections (BSIs) in patients with burns may result from burn wound infection, use of invasive devices such as central venous catheters, and translocation of the gastrointestinal flora.

OBJECTIVE

In this study, we investigated the distribution and antimicrobial drug resistance of causative pathogens in children with burns and the durational changes of microorganisms in the distribution of BSIs in children.

METHODS

This study was conducted at the Pediatric Burn Unit (PBU) of Dr. Behçet Uz Children Research and Training Hospital during the period of November 2008-April 2015. The study subjects were all the patients admitted to the PBU, in whom microorganisms were isolated at least from one of the cultures, including blood and catheter cultures.

RESULTS

Gram-positive bacteria were the most common causative agents of BSI in patients with burns (66.4%), followed by gram-negative bacteria (22.1%) and fungi (11.5%). The median duration of development of BSIs caused by gram-positive bacteria from the time of burn was 5 days (ranging from 2 to 54 days of burn), which was significantly shorter than that of BSIs caused by gram-negative bacteria (12 days) and fungal pathogens (13 days).

CONCLUSION

The etiologic agents of BSIs in children may differ from those in adults. Gram-negative drug-resistant bacteria such as multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii were important agents of BSI in patients with burns, especially in the long term; however, gram-positive bacteria should also be considered while deciding the antimicrobial therapy, especially in the early periods of burn.

How to Optimize the Use of Blood Cultures for the Diagnosis of Bloodstream Infections? A State-of-the Art

Bloodstream infection (BSI) is a major cause of death in developed countries and the detection of microorganisms is essential in managing patients. Despite major progress has been made to improve identification of microorganisms, blood culture (BC) remains the gold standard and the first line tool for detecting BSIs. Consensus guidelines are available to ensure optimal BSI procedures, but BC practices often deviate from the recommendations. This review provides an update on clinical and technical issues related to blood collection and to BC performance, with a special focus on the blood sample strategy to optimize the sensitivity and specificity of BCs.

Candida rugosa: a possible emerging cause of candidaemia in trauma patients

INTRODUCTION

Candida rugosa appears to be emerging as a distinctive cause of candidaemia in recent years. Candidaemia due to this species is important to recognise because of its decreased susceptibility to azoles.

MATERIALS AND METHODS

We retrospectively evaluated a cluster of C. rugosa candidaemia occurring in critically ill trauma patients from a level I trauma centre of India. During the period from July 2008 to September 2009, a total of 28 blood samples from 19 patients were found to be positive for C. rugosa. Genetic relatedness among 17 C. rugosa isolates were characterised by the random amplified polymorphic DNA (RAPD) assay using M13 primers. These isolates were also characterised for their susceptibility to four antifungal agents, amphotericin B, fluconazole, flucytosine and voriconazole.

RESULTS

In our study, 21% of C. rugosa isolates were resistant to fluconazole, whereas 100% susceptibility to amphotericin B, flucytosine and voriconazole was noted. Thirteen out of the 19 patients (68.4%) with C. rugosa candidaemia died. Of these, six had received antifungal therapy after confirmation of fungaemia.

DISCUSSION

Prior to this cluster, C. rugosa had never been identified as a cause of infection at our centre. Due to the retrospective nature of the evaluation of these cases, the source of this possible outbreak could not be traced. Nevertheless, to the best of our knowledge, this is the largest cluster of cases of C. rugosa candidaemia reported from a single institution in the English literature.

Evaluation of BacT/ALERT system for detection of Mycoplasma hominis in simulated blood cultures

We used simulated blood cultures inoculated with clinical isolates of Mycoplasma hominis to determine whether liquid media of the BacT/ALERT (Organon Teknika, Durham, N.C.) will support growth of this fastidious organism and whether its presence can generate a positive signal with the instrument. Viability of clinical isolates of M. hominis was maintained for 7 days in BacT/ALERT media, and organisms were able to multiply when 1% gelatin was added to neutralize the mycoplasmastatic effects of the sodium polyanetholsulfonate anticoagulant. Without the addition of gelatin to BacT/ALERT bottles, the mycoplasmas declined in numbers or became completely nonviable. Mycoplasmal growth was further enhanced in BacT/ALERT PF both supplemented with gelatin, arginine, and DNA in comparison to broth with only gelatin added. No BacT/ALERT bottles containing M. hominis in simulated blood cultures were flagged positive by the instrument, despite growth of microorganisms of up to 10(7) CFU/ml after incubation for up to 7 days, suggesting that inadequate CO(2) production or some other mechanism prevents the instrument from recognizing the presence of the organism and its metabolic products. The fastidious cultivation requirements and relatively slow growth of M. hominis warrant that dependence on automated systems and techniques designed to detect conventional bacteria will not be reliable for recovery of M. hominis and that specialized media and incubation conditions designed for optimum cultivation of mycoplasmas should be employed when this organism is suspected on clinical grounds.

Laboratory diagnosis of bacteremia and fungemia

Many of the variables that affect the laboratory diagnosis of bacteremia and fungemia have been addressed in this article. Whereas the scientific basis and principles for blood cultures are well-established, and the methodology has improved, the diagnosis of bacteremia and fungemia still depends greatly on the care that is taken in obtaining the specimens of blood and the skill of the clinician in interpreting positive results.

Four-day incubation for detection of bacteremia using the BACTEC 9240

Records of 29,356 blood cultures performed between April 1994 and April 1997, using the BACTEC 9240 continuous monitoring blood culture system, were reviewed retrospectively. From these, 3,127 blood culture vials became positive. Of 95 blood culture isolates detected after three days of incubation, 63 were recovered on day four and 32 on day five. Twenty-six contaminants were recovered on day four, and 21 on day five. Chart review was performed for all day four and five isolates that did not meet our definition of a contaminant. Of the 40 isolates that were clinically insignificant, 31 were recovered on day four, and nine on day five. Of eight clinically significant isolates, six were recovered on day four, and two on day five. Our data support a four-day incubation protocol for the recovery of all clinically significant bacteria with overall sensitivity reduced by only 0.06% when compared with a five-day protocol.

Comparison of the MB/BacT system with a revised antibiotic supplement kit to the BACTEC 460 system for detection of mycobacteria in clinical specimens

The MB/BacT system (MB/BacT) with a revised antibiotic supplement kit was compared with the BACTEC 460 system (BACTEC 460) in a test of 488 specimens submitted for mycobacterial culture from 302 patients. Twenty-four Mycobacterium tuberculosis isolates were detected by the BACTEC 460 versus 23 isolates by the MB/BacT. Mean time until detection of M. tuberculosis isolates identified by both systems was 11.9 days for the BACTEC 460 versus 13.7 days for the MB/BacT (P = 0.046). M. avium complex was detected in 12 specimens by the MB/BacT versus 10 specimens by the BACTEC 460. Only 8 of 14 (57%) M. avium isolates were detected by both systems, with a mean time until detection of 10.1 days for the BACTEC 460 and 14.2 days for the MB/BacT (P = 0.009). The BACTEC 460 and the MB/BacT detected M. gordonae in four specimens, but only a single specimen was positive by both systems. One M. fortuitum isolate and one of five M. kansasii isolates were recovered only by the BACTEC 460. The bacterial overgrowth rate was 7.0% for the MB/BacT versus 4.1% for the BACTEC 460. We found the MB/BacT to be comparable to the BACTEC 460 for mycobacterial detection. Even though time until detection with the MB/BacT was slightly longer (1.8 days longer for M. tuberculosis and 4.1 days for M. avium [mean values]) and the bacterial overgrowth rate was somewhat higher, the decreased labor, the availability of a computerized data management system, and the noninvasive, nonradiometric aspects of the MB/BacT offset these relative disadvantages and make it an acceptable alternative for use in the diagnostic laboratory.

Direct bacterial identification from positive BacT/Alert blood cultures using MicroScan overnight and rapid panels

Studies were conducted on a method of direct inoculation of MicroScan overnight and rapid panels from positive BacT/Alert blood culture bottles containing standard aerobic media to determine the correlation with inoculation of the corresponding panels with a standardized bacterial suspension obtained following subculture to agar. For Gram-negative organisms, 122 of 127 (96%) overnight panels and 85 of 118 (72%) rapid panels showed complete agreement with the standard method for species identification. Highest concordance (99%) occurred with Enterobacteriaceae inoculated directly into overnight panels. For Gram-positive organisms, 70 of 85 (82%) overnight panels and 45 of 86 (52%) rapid panels showed complete agreement. These findings suggest that direct inoculation of Gram-negative overnight MicroScan panels yields results most comparable to standard methods when Enterobacteriaceae are detected and allows reporting of results 18 to 24 h sooner. Direct inoculation of Gram-positive overnight or rapid panels and Gram-negative rapid panels from this blood culture medium did not yield acceptable identification results and is not recommended.

Direct susceptibility testing with positive BacT/Alert blood cultures by using MicroScan overnight and rapid panels

Studies were conducted on a method of direct inoculation of MicroScan dried overnight and of rapid panels with positive aerobic blood cultures obtained from the BacT/Alert to determine antimicrobial susceptibilities. Inocula were limited to specimens that appeared unimicrobic on Gram stain. Results were compared to those obtained from panels inoculated following subculture. For 133 gram-negative bacilli, there were 94.7 and 93.5% categorical agreements between direct and standard methods for all drugs tested with overnight and rapid panels, respectively. For 104 gram-positive cocci, there were 93.2 and 93.1% categorical agreements for overnight and rapid panels, respectively. The major error (false resistance) rate for gram negatives was 1.4% for overnight versus 0.7% for rapid panels. The very major error (false susceptibility) rate was 2.7% for overnight versus 8.1% for rapid panels. The total error rates were 1.6% for overnight panels and 1.5% for rapid panels. The major error rates for gram-positive direct susceptibility tests were 2.6% for overnight and 2.5% for rapid panels. The very major error rates were 8.8 and 7.2% for overnight and rapid panels, respectively. Total error rates were 3.6% for overnight and rapid gram-positive panels. These findings suggest that susceptibility results obtained from directly inoculated gram-negative overnight panels have the greatest correlation to those obtained by standard methods. When discrepant results occur with direct-susceptibility testing, they are more likely to show false susceptibility than false resistance.

Detection of bacteraemia in patients with fever and neutropenia using 16S rRNA gene amplification by polymerase chain reaction

Episodes of fever and neutropenia are common complications of treatment for cancer. The use of prophylactic and early empirical antibiotics has reduced mortality but decreases the sensitivity of diagnostic tests based on culture. The aim of this study was to determine the potential of a broad diagnostic approach (eubacterial) based on 16S rRNA gene amplification and sequencing to augment cultural methods of diagnosis of bacteraemia in patients with fever and neutropenia in a regional paediatric oncology centre. One hundred eleven patient-episodes of fever and neutropenia were evaluated during the study period, 17 of which were associated with positive blood cultures, as follows: Staphylococcus epidermidis (n = 6 episodes), Enterococcus faecium (n = 2), Streptococcus sanguis (n = 3), Streptococcus mitis (n = 3), Staphylococcus aureus (n = 1), Micrococcus spp. (n = 1), and Stenotrophomonas maltophilia (n = 1). Eubacterial polymerase chain reaction (PCR) detected bacterial DNA in nine of 11 blood culture-positive episodes for which a sample was available for PCR; the species identified by sequence analysis were identical to those derived from the conventional identification of the cultured isolates. Bacterial DNA was detected in 20 episodes (21 bacterial sequences) associated with negative blood cultures, 18 of which occurred in patients who were receiving antibiotics at the time of sample collection. The species presumptively identified by partial 16S rRNA gene sequencing were as follows: Pseudomonas spp. (n = 6 episodes), Acinetobacter spp. (n =5 ); Escherichia spp. (n = 3); Moraxella spp. (n = 3); Staphylococcus spp. (n = 2); Neisseria spp. (n = 1); and Bacillus spp. (n = 1). The results of this study suggest that molecular techniques can augment cultural methods in the diagnosis of bacteraemia in patients who have been treated with antibiotics.

Rapid diagnosis of Brucella bacteremia by using the BACTEC 9240 system

Almost 93% of 97 separate patient isolates of Brucella bloodstream infections were recovered within 5 days of incubation by using the BACTEC 9240 continuous-monitoring blood culturing system.

Bacteraemia during direct laryngoscopy and endotracheal intubation: a study using a multiple culture, large volume technique

Bacteraemia secondary to orotracheal intubation has been reported to occur in 0-5.3% of patients. Bacteraemia detection is dependent upon several factors including the volume of blood per culture and the number of cultures. Prior studies used small volumes of blood and one or two cultures, and may therefore have underestimated the incidence of bacteraemia. Sixty-two adult patients who underwent direct laryngoscopy and endotracheal intubation were studied. Baseline blood cultures were sterile in all patients. After intubation, four blood cultures were obtained in ten minutes, with 10 ml being evenly divided between aerobic and anaerobic media. Two patients (3.2%) became bacteraemic. This is a lower incidence than occurs in association with other procedures for which The American Heart Association does not recommend administration of prophylactic antibiotics. Therefore, prophylactic antibiotics are not recommended prior to direct laryngoscopy. However, when a prophylactic antibiotic is administered prior to surgery, it would be best to administer the antibiotic prior to direct laryngoscopy and intubation.

Volume of blood required to detect common neonatal pathogens

OBJECTIVE

To determine the minimum volume of blood and the absolute number of organisms required for detection of bacteremia and fungemia by an automated colorimetric blood culture system (BacT/Alert, Organon Teknika).

DESIGN

Common neonatal pathogens, Escherichia coli, Streptococcus agalactiae (group B streptococcus (GBS): one American Type Culture Collection (ATCC) strain and one clinical isolate), Staphylococcus epidermidis, and Candida albicans, were seeded into blood to produce bacteremia or fungemia with low colony counts (1 to 3 colony-forming units (CFU) per milliliter) and ultra-low colony counts (<1 CFU/ml). For each organism, 96 culture bottles were inoculated with either 0.25, 0.5, 1.0, or 4.0 ml of the two seeded blood concentrations. Blood culture bottles were incubated in the BacT/Alert device for 5 days, and time to positivity was noted when applicable. All bottles were subcultured on plated media.

DATA ANALYSIS

The Poisson statistic was used to calculate the probability of finding at least one viable CFU per inoculated culture bottle. The fraction of culture bottles with positive findings per group was divided by the probability of one or more organisms present to give the positivity index.

RESULTS

Plated subculture identified no growth of organisms not detected by the colorimetric detection system. The false-positive rate for the automated device was less than 1%. The positivity index for the GBS clinical isolate was 1.13, for the GBS ATCC isolate 0.96, for S. epidermidis 0.94, for C. albicans 0.97, and for E. coli 0.95. There was a statistically significant difference with time to positivity and inocula volume (p <0.01), but the difference was not clinically important.

CONCLUSIONS

If one or two viable colony-forming units are in the blood inoculated into culture media, the BacT/Alert system will detect growth rapidly. Because there appears to be a sizable subset of neonates who are at risk of sepsis with a colony count less than 4 CFU/ml, then a 0.5 ml inoculum of blood into the culture media is inadequate for sensitive and timely detection of bacteremia. One to two milliliters of blood should increase microorganism recovery in the face of low-colony-count sepsis.