Critical assessment of blood culture techniques: analysis of recovery of obligate and facultative anaerobes, strict aerobic bacteria, and fungi in aerobic and anaerobic blood culture bottles

Identification and Management of Fusobacterium Nucleatum Liver Abscess and Bacteremia in a Young Healthy Man

A 21-year-old previously healthy young man was admitted with five days of fever, persistent cough, worsening shortness of breath, and vomiting. On presentation, laboratory evaluation revealed extremely elevated procalcitonin and leukopenia followed by leukocytosis. The patient was started on empiric antibiotics. Further diagnostic evaluation after initiation of antibiotics included a computed tomography scan, which revealed a large hepatic abscess. Blood cultures obtained on admission grew Fusobacterium nucleatum; fluid obtained from the hepatic abscess also grew F. nucleatum. The patient’s antibiotic regimen was narrowed for specific coverage of F. nucleatum. The liver abscess was drained several times via image-guided percutaneous abscess drainage, with eventual resolution of the abscess. Patient received a prolonged course of intravenous antibiotics and, once stabilized, was discharged on two weeks of Augmentin. Here, we present a rare case of hepatic abscess and bacteremia due to F. nucleatum in a previously healthy young man with good oral hygiene. With this case, we aim to demonstrate the following: (1) the acute onset and rapid disease progression of F. nucleatum bacteremia and liver abscess; (2) how extreme procalcitonin elevation may serve to be a clinically useful early marker of F. nucleatum infection; and (3) the importance of early diagnosis, treatment, and definitive abscess drainage of F. nucleatum bacteremia and liver abscess.

Microflora analysis in the postchemotherapy patients of oral cancer

Background:

To assess changes in oral microflora in dental plaque from cancer patients within 7 days of the first course of chemotherapy and the relationship of the changes with mucositis.

Materials and Methods:

Thirty cancer patients, divided into a test group undergoing chemotherapy and a control group not undergoing chemotherapy, were enrolled in this pilot study. Oral microflora was cultured from three samples of dental plaque at t0 (before chemotherapy), t1 (1 day after chemotherapy), and t2 (7 days after chemotherapy). Single and crossed descriptive analyses were used to establish prevalence, and the Chi-square test was used to establish the statistical significance of the differences observed in distributions (significance level: P < 0.05).

Results:

In most patients (55%), oral microflora consisted mainly of Gram-positive cocci, while the remaining 45% of the bacterial flora also had periodontal-pathogenic species. No Porphyromonas gingivalis appeared in the test group. Actinobacillus was the least frequently found bacterium among periodontal pathogens in the test group, while Fusobacterium nucleatum was the most frequently found. No significant differences were found in quantitative bacterial changes between t0, t1, and t2 in either the test or control groups, or between the two groups. According to World Health Organization scores, oral mucositis developed in 10 patients (66.6%) in the test group.

Conclusions:

The results of this pilot study indicate that there were no changes in microflora in dental plaque in cancer patients within 7 days of the first course of chemotherapy. No correlations between oral mucositis and specific microorganisms were assessed.

Best Practices of Blood Cultures in Low- and Middle-Income Countries

Bloodstream infections (BSI) have a substantial impact on morbidity and mortality worldwide. Despite scarcity of data from many low- and middle-income countries (LMICs), there is increasing awareness of the importance of BSI in these countries. For example, it is estimated that the global mortality of non-typhoidal Salmonella bloodstream infection in children under 5 already exceeds that of malaria. Reliable and accurate diagnosis of these infections is therefore of utmost importance. Blood cultures are the reference method for diagnosis of BSI. LMICs face many challenges when implementing blood cultures, due to financial, logistical, and infrastructure-related constraints. This review aims to provide an overview of the state-of-the-art of sampling and processing of blood cultures, with emphasis on its use in LMICs. Laboratory processing of blood cultures is relatively straightforward and can be done without the need for expensive and complicated equipment. Automates for incubation and growth monitoring have become the standard in high-income countries (HICs), but they are still too expensive and not sufficiently robust for imminent implementation in most LMICs. Therefore, this review focuses on "manual" methods of blood culture, not involving automated equipment. In manual blood cultures, a bottle consisting of a broth medium supporting bacterial growth is incubated in a normal incubator and inspected daily for signs of growth. The collection of blood for blood culture is a crucial step in the process, as the sensitivity of blood cultures depends on the volume sampled; furthermore, contamination of the blood culture (accidental inoculation of environmental and skin bacteria) can be avoided by appropriate antisepsis. In this review, we give recommendations regarding appropriate blood culture sampling and processing in LMICs. We present feasible methods to detect and speed up growth and discuss some challenges in implementing blood cultures in LMICs, such as the biosafety aspects, supply chain and waste management.

Pediatric Anaerobic Blood Culture Practices in Industrialized Countries

BACKGROUND

Routine anaerobic blood culture collection in febrile children is controversial, as clinicians try to account for the severe but relative infrequency of anaerobic bacteremia. Furthermore, clinical and laboratory practice variation among institutions may lead to potentially inaccurate epidemiological data. Our goal was to assess blood culture practices in pediatric patients throughout an international network of hospitals in industrialized countries.

METHODS

We conducted a survey of current clinical and laboratory practice patterns in a convenience sample of international institutions participating in 6 pediatric emergency research networks in the US, Canada, Europe, Australia, and New Zealand. A lead clinician at each institution queried institutional practices from the emergency department, pediatric intensive care unit, and oncology medical directors. The microbiology director at each institution completed the laboratory survey.

RESULTS

Sixty-five of 160 (41%) invited institutions participated in the survey. Routine anaerobic blood cultures are collected in 30% of emergency departments, 30% of intensive care units, and 48% of oncology wards. Reasons for restricting anaerobic culture collection included concerns regarding blood volume (51%), low pretest probability (22%), and cost-effectiveness (16%). The most common reasons institutions allow for selectively obtaining anaerobic cultures are clinical suspicion (64%) and patients who are immunosuppressed (50%). The microbiology survey showed variation in systems, although most use the BACTEC™ culture system and MALDI-TOF for organism identification.

CONCLUSIONS

There is broad variation in anaerobic blood culture practices among a network of pediatric hospitals in industrialized countries.

Judicious utilization of healthcare resources: reducing unindicated pediatric anaerobic blood cultures in a pediatric hospital

The decline in anaerobic infections in the past 15 years has resulted in healthcare professionals questioning the need for routine anaerobic blood cultures. In this study, we extracted baseline aerobic and anaerobic blood culture rates over the past 10 years (2001-2010) from our pediatric wards. A questionnaire survey of doctors was conducted to gather their views regarding anaerobic blood cultures. Interventions such as physician education were introduced over 6 months to reduce unindicated anaerobic blood cultures. Furthermore, the rates of blood cultures were tracked over time after intervention. Before intervention, 85% of doctors surveyed routinely ordered anaerobic blood cultures, 90% were unaware of any guidelines for anaerobic blood cultures, and 100% were unaware of the costs. The combination of physician education and restrictive interventions resulted in an 80% reduction in the number of anaerobic blood cultures performed and processed, which translated into savings of USD $2,883 per week, with projected savings of USD $145,560 annually.

Prospective study of the clinical performance of three BACTEC media in a modern emergency department: Plus Aerobic/F, Plus Anaerobic/F, and Anaerobic Lytic/F

The performance of 3 blood culture bottles (BACTEC Plus Aerobic/F, Plus Anaerobic/F, and Anaerobic Lytic/F) were analyzed with clinical specimens collected from 688 Emergency Department patients. A total of 270 strains belonging to 33 species were identified, with E. coli and S. aureus as the most frequently detected. Overall recovery rate (RR) of bacteria and yeast was equivalent in the Plus Aerobic/F vials (208 of 270 isolates; 77.0%) and Anaerobic Lytic/F vials (206 isolates; 76.3%) and significantly better than in the Plus Anaerobic/F vials (189 isolates; 70.0%). Median time to detection (TTD) was earliest with the Anaerobic Lytic/F vials (12.0h) compared with the Plus Aerobic/F (14.6h) and Plus Anaerobic/F vials (15.4h). Positivity rate (PR) was similar for Anaerobic Lytic/F vials (76.9%) and Plus Aerobic/F vials (76.5%), but better if compared with Plus Anaerobic/F vials (69.4%). The PR and TTD for the combination of Plus Aerobic/F with Anaerobic Lytic/F (94.5% and 12.3h, respectively) was significantly better than with Plus Aerobic/F with Plus Anaerobic/F (87.8% and 14.1h).

Anaerobic bacteraemia: a 10-year retrospective epidemiological survey

In order to identify current trends in anaerobic bacteraemia, a 10-year retrospective study was performed in the University Hospital Brussel, Belgium. All clinically relevant bacteraemia detected from 2004 until 2013 were included. Medical records were reviewed in an attempt to define clinical parameters that might be associated with the occurrence of anaerobic bacteraemia. 437 of the isolated organisms causing anaerobic bacteraemia were thawed, subcultured and reanalyzed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). There were an average of 33 cases of anaerobic bacteraemia per year during 2004-2008 compared to an average of 27 cases per year during 2009-2013 (P = 0.017), corresponding to a decrease by 19% between the first and the latter period. Also, the total number of cases of anaerobic bacteraemia per 100,000 patient days decreased from 17.3 in the period from 2004 to 2008 to 13.7 in the period 2009 to 2013 (P = 0.023). Additionally, the mean incidence of anaerobic bacteraemia decreased during the study period (1.27/1000 patients in 2004 vs. 0.94/1000 patients in 2013; P = 0.008). In contrast, the proportion of isolated anaerobic bacteraemia compared to the number of all bacteraemia remained stable at 5%. Bacteroides spp. and Parabacteroides spp. accounted for 47.1% of the anaerobes, followed by 14.4% Clostridium spp., 12.6% non-spore-forming Gram-positive rods, 10.5% anaerobic cocci, 8.2% Prevotella spp. and other Gram-negative rods and 7.1% Fusobacterium spp. The lower gastrointestinal tract (47%) and wound infections (10%) were the two most frequent sources for bacteraemia, with the origin remaining unknown in 62 cases (21%). The overall mortality rate was 14%. Further studies focusing on the antimicrobial susceptibility and demographic background of patients are needed to further objectify the currently observed trends.

Changes in microflora in dental plaque from cancer patients undergoing chemotherapy and the relationship of these changes with mucositis: A pilot study

BACKGROUND

To assess changes in oral microflora in dental plaque from cancer patients within 7 days of the first course of chemotherapy, and the relationship of the changes with mucositis.

MATERIAL AND METHODS

Thirty cancer patients, divided into a test group undergoing chemotherapy and a control group no undergoing chemotherapy, were enrolled in this pilot study. Oral microflora were cultured from three samples of dental plaque at t0 (before chemotherapy), t1 (1 day after chemotherapy) and t2 (7 days after chemotherapy). Single and crossed descriptive analyses were used to establish prevalence, and the χ² test was used to establish the statistical significance of the differences observed in distributions (significance level: P<0.05).

RESULTS

In most patients (57%), oral microflora consisted mainly of Gram-positive cocci, while the remaining 43% of the bacterial flora also had periodontal-pathogenic species. No Porphyromonas gingivalis appeared in the test group. Actinobacillus was the least frequently found bacterium among periodontal pathogens in the test group, while Fusobacterium nucleatum was the most frequently found. No significant differences were found in quantitative bacterial changes between t0, t1 and t2 in either the test or control groups, or between the two groups. According to World Health Organization scores, oral mucositis developed in 10 patients (66.6%) in the test group.

CONCLUSIONS

The results of this pilot study indicate that there were no changes in microflora in dental plaque in cancer patients within 7 days of the first course of chemotherapy. No correlations between oral mucositis and specific microorganisms were assessed.

Current approaches to the diagnosis of bacterial and fungal bloodstream infections in the intensive care unit

Healthcare systems spend considerable resources collecting and processing blood cultures for the detection of blood stream pathogens. The process is initiated with the collection of blood cultures that depend upon proper skin disinfection, collection of an adequate number of specimens and volume of blood, and prompt processing in a sensitive culture system. Complementing blood cultures and gaining in use are techniques such as nucleic acid amplification tests and mass spectroscopy that allow clinical laboratories to detect and identify organisms from blood cultures substantially faster than conventional systems. Furthermore, certain resistance mutations can be detected within hours of organism detection, thus providing valuable guidance to clinicians who strive to initiate the appropriate antimicrobial therapy as rapidly as possible, and who wish to discontinue unnecessary drugs expeditiously. Molecular and mass spectroscopy techniques are changing sepsis diagnosis rapidly and will provide far more specific information far more quickly, but the performance characteristics of these systems must be understood by intensivists who use such information to guide their patient management.

Current approaches to the diagnosis of bacterial and fungal bloodstream infections in the intensive care unit

Healthcare systems spend considerable resources collecting and processing blood cultures for the detection of blood stream pathogens. The process is initiated with the collection of blood cultures that depend upon proper skin disinfection, collection of an adequate number of specimens and volume of blood, and prompt processing in a sensitive culture system. Complementing blood cultures and gaining in use are techniques such as nucleic acid amplification tests and mass spectroscopy that allow clinical laboratories to detect and identify organisms from blood cultures substantially faster than conventional systems. Furthermore, certain resistance mutations can be detected within hours of organism detection, thus providing valuable guidance to clinicians who strive to initiate the appropriate antimicrobial therapy as rapidly as possible, and who wish to discontinue unnecessary drugs expeditiously. Molecular and mass spectroscopy techniques are changing sepsis diagnosis rapidly and will provide far more specific information far more quickly, but the performance characteristics of these systems must be understood by intensivists who use such information to guide their patient management.

Comparative evaluation of paired blood culture (aerobic/aerobic) and single blood culture, along with clinical importance in catheter versus peripheral line at a tertiary care hospital

PURPOSE

Paired blood culture (PBC) is uncommon practice in hospitals in India, leading to delayed and inadequate diagnosis. Also contamination remains a critical determinant in hampering the definitive diagnosis.

OBJECTIVES

To establish the need of PBC over single blood culture (SBC) along with the degree of contamination, this comparative retrospective study was initiated.

MATERIALS AND METHODS

We processed 2553 PBC and 4350 SBC in BacT/ALERT 3D (bioMerieux) between October 2010 and June 2011. The positive cultures were identified in VITEK 2 Compact (bioMerieux). True positivity and contaminants were also analyzed in 486 samples received from catheter and peripheral line.

RESULTS

Out of 2553 PBC samples, positivity was seen in 350 (13.70%). In 4350 SBC samples, positivity was seen in 200 samples (4.59%). In PBC true pathogens were 267 (10.45%) and contaminants were 83 (3.25%), whereas in SBC 153 (3.51%) were true positives and contaminants were 47 (1.08%). Most of the blood cultures (99.27 %) grew within 72 h and 95.8% were isolated within 48 h. In 486 PBCs received from catheter/periphery (one each), catheter positivity was found in 85 (true positives were 48, false positives 37). In peripheral samples true positives were 50 and false positives were 8.

CONCLUSION

Significantly higher positive rates were seen in PBCs compared with SBCs. Automated blood culture and identification methods significantly reduced the time required for processing of samples and also facilitated yield of diverse/rare organisms. Blood culture from catheter line had higher false positives than peripheral blood culture. Thus every positive result from a catheter must be correlated with clinical findings and requires further confirmation.

Evaluation of routine enteric pathogens in hospitalized patients: A Canadian perspective

Diarrhea is a frequently encountered problem in hospitalized patients. Since nosocomial spread of routine enteric pathogens such as Salmonella species, Shigella species, Campylobacter species and Escherichia coli O:157 H:7 seldom occurs, testing for these organisms in patients hospitalized for longer than three days has been questioned. The goal of this study was to determine the length of hospitalization preceding detection of routine enteric pathogens and Clostridium difficile cytotoxin, and to develop guidelines for enteric cultures from hospitalized patients. The enteric pathogens detected in 1991 were C difficile toxin B(+), 77%; Campylobacter species, 10%; Salmonella species, 9%; E coli O:157 H:7, 3%; and Shigella species, 1%. For 1992, these numbers were 86%, 9%, 3%, 2% and 0%, respectively. None of the routine enteric pathogens isolated in 1991 or 1992 was detected in patients after their second day of hospitalization. Routine cultures for enteric pathogens on hospitalized patients were eliminated in February 1993, and physician ordering practices were monitored. With the exception of one campylobacter isolate per year, all routine enteric pathogens isolated in 1993 and 1994 were detected by the second day of hospitalization. Compliance with the changed protocol was 76% measured over a four-month period in 1993 and 74% over the year 1994. Savings of $3,648.10 were associated with rejecting 191 'inappropriate' specimens in 1994. It was concluded that routine enteric cultures are unnecessary for patients hospitalized more than two days, and that appreciable financial savings can be achieved if revised protocols for processing stool cultures are instituted. However, when enteric protocol changes are in place compliance must be evaluated to ensure appropriate utilization.

Five-year retrospective epidemiological survey of anaerobic bacteraemia in a university hospital and rewiew of the literature

In spite of the developments in microbiological methods, blood cultures remain the cornerstone for the diagnosis of bacteraemia. Classically, minimum of two bottles are collected on a routine basis: an aerobic bottle, allowing preferential growth of aerobic and facultative anaerobic microorganisms, and an anaerobic bottle, providing suitable environment for strict anaerobic bacteria. Recent reports have documented a decrease in anaerobic bacteraemias and have questioned the need for routine anaerobic blood cultures. Bacteraemia due to anaerobic organisms occurs in 0.5-12% of blood cultures worldwide; however, recent studies from Europe and the USA presented inconsistent data regarding the prevalence of anaerobic bacteraemias between 1993 and 2006. The aims of this retrospective survey were to determine the prevalence of bacteraemias due to anaerobic bacteria and evaluate the importance of anaerobic blood cultures in a university hospital in Szeged, Hungary. We examined the occurrence of bacteraemias due to anaerobic bacteria during a 5-year period, from January 2005 to 2009, in order to identify current trends of anaerobic bacteraemias in our university.

A Critical Appraisal of the Role of the Clinical Microbiology Laboratory in the Diagnosis of Bloodstream Infections

The detection of bloodstream infections is one of the most important functions of clinical microbiology laboratories. Despite advances in blood culture technology and clinical studies that have focused on the detection of bacteremia and fungemia, perfection has not been achieved and uncertainties persist. This review provides perspectives on a number of areas, including the recommended number of blood cultures, duration of incubation of blood cultures, use of anaerobic, in addition to aerobic, blood culture media, value of the lysis-centrifugation method, processing and reporting of probable blood culture contaminants, and limitations of current blood culture methods and systems. We also address the handling of blood cultures in point-of-care locations that lack full microbiology capabilities.

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.

[Diagnostic reliability of anaerobic blood cultures in bacteremias from a critical care unit]

BACKGROUND AND OBJECTIVE

This is a descriptive study of bacteraemias diagnosed in ICU with an analysis of the diagnostic reliability of anaerobic blood cultures.

PATIENTS AND METHOD

Analysis of all positive blood cultures in an Intensive Care Unit from May 2005 to October 2007.

RESULTS

The overall incidence of true bacteraemia was 6,1% of admissions. Out of 100 patients, there were 73 bacteraemias and 52 contaminated cultures. Samples with contaminated cultures were drawn 6,27 days earlier (CI 95% 0,61-11,94 Sig:0,03) than true bacteraemia. Most frequent micro organisms were cocci gram positive: 43 cases (58,9%) (coagulase-negative staphylococci was the most frequent: 30 or 41% of all bacteraemia)) Sig=0,001 in relation with gram negatives. Anaerobic micro organisms were not detected. Candidemias were found in 10 cases (13,7%). The most frequent causes of bacteraemia in this study were catheter-related infections with 36 cases (49,3% Sig<0,005), followed by digestive origin infections in 14 (19,2%). Of all bacteremic episodes (73 bacteraemia), 66 (90,4%) were isolated in aerobic blood cultures, and 58 (79,5%) were in anaerobic ones, with a difference of 10,9% Sig:0,06. When only intrahospitalary bacteraemias were analyzed, there was a difference of 13,56% of more yields in aerobic blood cultures; Sig:0,04 (IC 95% 0,8%-26%)). Candidemias were isolated only in aerobic blood cultures; Sig:0,001. When analyzing coagulase negative staphylococci, there were 30 bacteraemias and 41 contaminated samples. 62 (87,3%) were isolated in aerobic blood cultures and 50 (70,4%) in anaerobic ones, with a difference of 16,9% Sig=0,01,CI 95%(3%-30%).

CONCLUSIONS

In the Critical Care Unit, it would be possible to change the anaerobic blood cultures by aerobic ones to diagnose bacteraemias of intrahospitalary acquisition. This fact should be analyzed with others studies.

Is anaerobic blood culture necessary? If so, who needs it?

BACKGROUND

The role of anaerobic blood cultures is not validated, although they are drawn routinely.

METHODS

We performed a retrospective chart review at a private hospital in Japan for patients admitted between July 1, 2004 to June 30, 2005 to determine patient characteristics resulting in anaerobic blood culture.

RESULTS

During the study period, 17,775 blood culture bottles were sent for the analysis, and 2132 bottles (12.0%) were positive for microbial growth. Bacteria were grown from 958 anaerobic bottles (44.7%), and 719 (33.7%) of those were judged to represent real infections, which accounted for 410 cases of bacteremia. Only 47 cases (11.5%) were detected by anaerobic cultures alone. Among those 47, obligate anaerobes represented 12 cases. Clinical evaluation could have predicted 7 of 12 cases of obligate anaerobic bacteremia. In the remaining 5 cases, the source of bacteremia was unclear. There were 2.7 cases of anaerobic bacteremia per 1000 blood cultures. The mortality attributable to anaerobic bacteremia was 50%. Among bacteremic cases not caused by obligate anaerobes yet diagnosed solely by anaerobic bottles, either the standard 2 sets of blood were not taken or their clinical outcomes were favorable.

CONCLUSION

Anaerobic blood culture can be avoided in most cases. Anaerobic blood culture may be most helpful when (1) bacteremia because of obligate anaerobes is clinically suspected, (2) patients are severely immunocompromised, and (3) source of bacteremia is not identified by clinical evaluation.

Bloodstream infections: evolution and trends in the microbiology workload, incidence, and etiology, 1985-2006

Information available on bloodstream infection (BSI) is usually restricted to short periods of time, certain clinical backgrounds, or specific pathogens, or is just outdated. We conducted the current prospective study of patients with BSI in a 1750-bed teaching hospital to evaluate workload trends and the incidence and etiology of BSI in a general hospital during the last 22 years, including the acquired immunodeficiency syndrome (AIDS) era. The main outcome measures were laboratory workload, trends in incidence per 1000 admissions and per 100,000 population of different microorganisms, and the impact of the human immunodeficiency virus (HIV) epidemic in the period 1985-2006.From 1985 to 2006 we had 27,419 episodes of significant BSI (22,626 patients). BSI incidence evolved from 16.0 episodes to 31.2/1000 admissions showing an annual increase of 0.83 episodes/1000 admissions (95% confidence interval, 0.61-1.05; p < 0.0001). The evolution of the incidence per 1000 admissions and per 100,000 population of different groups of microorganisms was as follows: Gram positives 8.2 to 15.7/1000 admissions and 66.8 to 138.3/100,000 population; Gram negatives 7.8 to 16.2/1000 admissions and 63.5 to 141.9/100,000 population; anaerobes 0.5 to 1.3/1000 admissions and 4.1 to 11.7/100,000 population; and fungi 0.2 to 1.5/1000 admissions and 1.7 to 12.5/100,000 population. All those differences were statistically significant. We observed the emergence of multiresistant Gram-positive and Gram-negative microorganisms. At least 2484 episodes of BSI (9.1%) occurred in 1822 patients infected with HIV. The incidence of BSI in HIV-infected patients increased from 1985 and reached a peak in 1995 (17.6% of BSI). Since 1995, the decrease was continuous, and in 2006 only 3.9% of all BSI episodes occurred in HIV-positive patients in our institution. We conclude that the BSI workload has increased in modern microbiology laboratories. Gram-positive pathogens have overtaken other etiologic agents of BSI. Our observation shows the remarkable escalation of some resistant pathogens, and the rise and relative fall of BSI in patients with HIV.

Relevance of routine use of the anaerobic blood culture bottle

Using the BacT/Alert automated system, we conducted a 1-year retrospective study on blood cultures, focusing on the relevance of routine use of the anaerobic bottle. The rate of patients with positive blood cultures was 19.7%. Among these, 13.5% had a positive anaerobic bottle in the absence of any aerobic bottle, and 2/3 of these grew with nonobligate anaerobes. These patients were hospitalized in 20 out of 26 wards of the hospital group. For 65.4% of the monomicrobial-positive blood cultures growing Enterobacteriaceae, the anaerobic bottle detected growth earlier than the corresponding aerobic bottle. These data suggest that, in our institution, the use of an anaerobic bottle is still relevant.

Reemergence of anaerobic bacteremia

BACKGROUND

During 1974-1988, the incidence of anaerobic bacteremia at the Mayo Clinic (Rochester, MN) decreased. This trend occurred nationally, prompting calls for discontinuation of routine anaerobic blood cultures. However, recently, the sites of anaerobic infection have been shown not to be as predictable as once thought, and since 1993, the incidence of anaerobic bacteremia has increased significantly in our medical center.

METHODS

Records from the Mayo Clinic Division of Clinical Microbiology were used to tabulate the number of cases of anaerobic bacteremia in patients at the clinic for the 12-year period from 1993 through 2004. Medical records for patients with anaerobic bacteremia were reviewed from the periods of 1993-1994 and 2004 to identify differences between these 2 patient populations with different rates of bacteremia.

RESULTS

The mean incidence of anaerobic bacteremias increased from 53 cases per year during 1993-1996 to 75 cases per year during 1997-2000 to 91 cases per year during 2001-2004 (an overall increase of 74%). The total number of cases of anaerobic bacteremia per 100,000 patient-days increased by 74% (P<.001). The number of anaerobic blood cultures per 1000 cultures performed increased by 30% (P=.002). Organisms from the Bacteroides fragilis group, other species of Bacteroides, and Clostridium species were most commonly isolated.

CONCLUSIONS

Anaerobic bacteremia has reemerged as a significant clinical problem. Although there are probably multiple reasons for this change, the increasing number of patients with complex underlying diseases makes the clinical context for anaerobic infections less predictable than it once was. Anaerobic blood cultures should be routinely performed in medical centers with a patient population similar to ours.

Updated review of blood culture contamination

Blood culture contamination represents an ongoing source of frustration for clinicians and microbiologists alike. Ambiguous culture results often lead to diagnostic uncertainty in clinical management and are associated with increased health care costs due to unnecessary treatment and testing. A variety of strategies have been investigated and employed to decrease contamination rates. In addition, numerous approaches to increase our ability to distinguish between clinically significant bacteremia and contamination have been explored. In recent years, there has been an increase in the application of computer-based tools to support infection control activities as well as provide clinical decision support related to the management of infectious diseases. Finally, new approaches for estimating bacteremia risk which have the potential to decrease unnecessary blood culture utilization have been developed and evaluated. In this review, we provide an overview of blood culture contamination and describe the potential utility of a variety of approaches to improve both detection and prevention. While it is clear that progress is being made, fundamental challenges remain.

Using the polymerase chain reaction coupled with denaturing gradient gel electrophoresis to investigate the association between bacterial translocation and systemic inflammatory response syndrome in predicted acute severe pancreatitis

AIM

To investigate the use of PCR and DGGE to investigate the association between bacterial translocation and systemic inflammatory response syndrome in predicted severe AP.

METHODS

Patients with biochemical and clinical evidence of acute pancreatitis and an APACHE II score > or = 8 were enrolled. PCR and DGGE were employed to detect bacterial translocation in blood samples collected on d 1, 3, and 8 after the admission. Standard microbial blood cultures were taken when there was clinical evidence of sepsis or when felt to be clinically indicated by the supervising team.

RESULTS

Six patients were included. Of all the patients investigated, only one developed septic complications; the others had uneventful illness. Bacteria were detected using PCR in 4 of the 17 collected blood samples. The patient with sepsis was PCR-positive in two samples (taken on d 1 and 3), despite three negative blood cultures. Using DGGE and specific primers, the bacteria in all blood specimens which tested positive for the presence of bacterial DNA were identified as E coli.

CONCLUSION

Our study confirmed that unlike traditional microbiological techniques, PCR can detect the presence of bacteria in the blood of patients with severe AP. Therefore, this latter method in conjunction with DGGE is potentially an extremely useful tool in predicting septic morbidity and evaluating patients with the disease. Further research using increased numbers of patients, in particular those patients with necrosis and sepsis, is required to assess the reliability of PCR and DGGE in the rapid diagnosis of infection in AP.

Validation of performance of plastic versus glass bottles for culturing anaerobes from blood in BacT/ALERT SN medium

To validate performance, we compared the new plastic BacT/ALERT (bioMérieux, Durham, NC) SN bottle to the current glass SN bottle with samples of blood obtained for culture from adults and found them comparable for both recovery and speed of detection of microorganisms. We conclude that the safety advantage of plastic bottles can be achieved without compromising performance.

Decreasing the use of anaerobic culture bottles in selected febrile patients--is it reasonable?

BACKGROUND

Two sets of blood cultures are routinely obtained from febrile patients in the medical wards. The purpose of the present study was to evaluate the distribution of the aerobic versus anaerobic isolates in such patients and to examine the rationale of reducing the number of anaerobic culture bottles in selected patients.

METHODS

A retrospective analysis was performed of all febrile patients admitted to medical wards during 1998. Febrile patients from whom at least two sets of blood cultures were drawn and who had a bacterial isolation in at least one bottle were included.

RESULTS

A total of 317 patients were included in the analysis. Some 98.5% of all isolates were aerobic pathogens. Only 1.5% of all isolates (5/317) included obligatory anaerobes. The rate of isolation in a single anaerobic bottle was 8.5%. Analysis of the available files of patients with a single anaerobic positive bottle demonstrated that an adequate antibacterial agent was administered empirically in most of the cases (93%).

CONCLUSIONS

We conclude that in carefully selected medical patients suspected of having an infectious disease, it is reasonable to obtain one anaerobic and two aerobic bottles rather than two full sets. Such an approach is clinically safe and will cut expenses on culture bottles and laboratory staff work. This approach should be examined in a prospective, randomized study.

Value of anaerobic blood cultures in pediatrics

The aim of the study presented here was to evaluate the utility of anaerobically incubated blood cultures for detecting infections in pediatric patients. During a 2-year period 9,165 pediatric blood samples were processed, and significant microorganisms were recovered from 497 (5.4%) of them. Only two of the microorganisms isolated were strictly anaerobic. Of the total isolates, 13% were detected in anaerobic bottles solely. Considering that the quantity of blood available from pediatric patients for blood cultures is usually small, it may be reasonable to limit the use of anaerobic blood cultures to patients with the highest risk.

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.

[Antimicrobial susceptibility and frequency of occurrence of clinical blood isolates in Sfax-Tunisia (1993-1998)]

Antimicrobial susceptibility and frequency of occurrence of clinical blood isolates in Sfax-Tunisia (1993-1998). The choice of antimicrobial therapy for the treatment of bacteremia is often empirical and based on the knowledge of susceptibility profiles of the most common bacteria causing such infections. This study determines the bacterial etiology of bacteremic episodes and antimicrobial susceptibility patterns recorded at a teaching hospital, from January 1993 to December 1998. We collected 2979 strains responsible for bacteremia. Gram negative bacteria were predominant (60%). The organisms recovered most frequently were Staphylococcus aureus (18.9%), Escherichia coli (14.7%), Klebsiella pneumoniae (14%) and Pseudomonas aeruginosa (7.6%). The incidence of resistance to methicillin were 17.4% for Staphylococcus aureus and 26.8% for coagulase negative Staphylococcus. No resistance to glycopeptides was observed among the enterococci and staphylococci studied. 27.7% of enterobacteriaceae were resistant to third generation cephalosporins. Imipenem was the most active agent against gram negative bacteria. To carry out a surveillance of bacteremic episodes occurring at every hospital, it is necessary to provide valuable information which should be the basis for effective empiric therapy.

Detection of bacteria and fungi in BacT/Alert standard blood-culture bottles

Incubation periods of aerobic (AE) and anaerobic (AN) blood-culture bottles with the BacT/Alert system were assessed in our laboratory. We reviewed the results of 6229 blood-culture sets collected at Kyoto University Hospital from January 1999 to December 2000. Of these sets, 731 (11.7%) were positive for bacteria or yeast. Excluding 87 sets with growth evidence on arrival, of the 644 positive blood-culture sets from 341 patients, a total of 691 organisms were isolated. Of the 691 organisms, 413 (59.8%) were recovered from both bottles, 206 (29.8%) were recovered only from the AE bottle, and 72 (10.4%) were recovered only from the AN bottle. The AE bottle was significantly superior to the AN bottle in terms of both recovery rate and detection time for overall organisms, but there was no significant difference in detection time for facultative anaerobic bacteria between the two bottles. Of the 691 organisms, 530 (76.7%) were classified as usual pathogens. Of the 530 usual pathogens, 501 (94.5%) were recovered in at least one bottle of each set within the first 3 days, and 523 (98.7%) within the first 5 days of incubation. Twenty-nine organisms initially isolated on day 4 or later were recovered from 19 patients. Of these, chart reviews indicated that 21 organisms recovered from 11 patients were considered clinically significant bacteria, and the reviews also revealed that no patient had a treatment plan altered based on the results of positive blood culture. Seven organisms initially isolated on day 6 or later were recovered from 7 patients. Chart reviews revealed that 5 of these organisms from 5 patients were considered to be clinically significant. In conclusion, if the incubation period had been less than 3 days, 11 patients with clinically significant bacteremia or fungemia, (3.2% of all patients with bacteremia or fungemia) would have been undiagnosed. Similarly, with an incubation period of 5 days, 5 such patients (1.5%) would have been undiagnosed.

Diagnostic methods. Current best practices and guidelines for isolation of bacteria and fungi in infective endocarditis

As the etiological character of IE changes, the microbiological tools used to confirm the diagnosis have also evolved. Here the authors have reviewed the current methods for optimal laboratory diagnosis of bacterial and fungal endocarditis using traditional growth-based technologies and offered good practice guidelines and recommendations. Newer techniques will be required to improve sensitivity of detection for known organisms and to identify emerging or as-yet unknown pathogens (see article by Lepidi et al in this issue).

Anaerobic bacteremia: the yield of positive anaerobic blood cultures: patient characteristics and potential risk factors

The anaerobic blood culture (AN) bottle is routinely used in Japan with little discussion as to its justification or validity. We retrospectively studied the AN bottle yield of obligate anaerobes and the characteristics of, and potential risk factors in, patients with anaerobic bacteremia during a 2-year period (1999-2000) at four university hospitals and one community hospital. Thirty-four of 18,310 aerobic and anaerobic blood culture sets from 6,215 patients taken at the university hospitals, and 35 of 2,464 samples taken from 838 patients at the community hospital, yielded obligate anaerobes. Bacteroides species and Clostridium species accounted for 60% of the isolates. Fifty-seven patients from 69 blood culture sets containing anaerobes had clinically significant anaerobic bacteremia. Among these 57 patients, 24 (49%) were oncology patients, 40 (70%) had an obvious source of anaerobic infection, 15 (26%) had recent surgery and/or were in an immunosuppressed state. We concluded that the recovery rate of obligate anaerobes isolated from AN bottles was low, and the patients with anaerobic bacteremia had limited number of underlying diseases or potential risk factors for anaerobic infections. Therefore, anaerobic blood cultures may be selectively used according to the potential risk for anaerobic infections.

Comparison of recovery of blood culture isolates from two BacT/ALERT FAN aerobic blood culture bottles with recovery from one FAN aerobic bottle and one FAN anaerobic bottle

Traditionally, a routine blood culture for adult patients consisted of paired aerobic and anaerobic bottles, but the routine use of an anaerobic blood culture bottle has been challenged in recent years. In this study, we compared the recovery of two FAN aerobic bottles with one FAN aerobic and one FAN anaerobic bottle. Each pair of bottles was collected by a separate collection procedure, and each bottle held a recommended 8- to 12-ml draw. A total of 704 clinically significant isolates were recovered from 8,620 sets (17,240 pairs), with 487 (69.2%) isolates recovered from one or both bottles in each pair of bottles, 86 isolates (12.2%) recovered only from the FAN aerobic-FAN aerobic pair, and 131 isolates (18.6%) recovered only from the FAN aerobic-FAN anaerobic pair. Significantly more total organisms (P = 0.002), gram-positive cocci (P = 0.03), Staphylococcus aureus (P = 0.05), Enterobacteriaceae other than Escherichia coli (P = 0.02), and anaerobes (P = 0.01) were recovered from the FAN aerobic-FAN anaerobic pair than from the FAN aerobic-FAN aerobic pair. A separate analysis was performed on the 618 isolates that were recovered from the FAN aerobic-FAN anaerobic pair to compare recovery by bottle type. Significantly more S. aureus (P = 0.005) and anaerobes (P < 0.001) were recovered from the FAN anaerobic bottle, while significantly more coagulase-negative staphylococci (P = 0.01), Streptococcus pneumoniae (P = 0.03), and other gram-negative bacilli (P = 0.004) were recovered from the FAN aerobic bottle. These results support the routine use of a FAN anaerobic bottle for use in the culture of blood with the BacT/ALERT system in our institution. These results also suggest that the decision of whether to routinely utilize an anaerobic blood culture bottle should be influenced by the overall recovery of bacteria and yeast, the recovery of specific types of bacteria or yeast, the medium type, and the blood culture system utilized by the laboratory.

Use of simulated blood cultures for time to detection comparison between BacT/ALERT and BACTEC 9240 blood culture systems

In order to avoid the influence of pre-analytical steps, the following study was performed by using sterile blood spiked with defined loads of microorganisms as inoculum. Time-to-Detection (TTD) was evaluated for the most frequently encountered bacteria and fungi in septicemia, comparing two commercially available blood culture systems, BACTEC 9240 (Becton Dickinson) and BacT/ALERT (Organon Teknika). A specific medium, Bactec Mycosis IC/F (Becton Dickinson), was compared with the Bactec Plus Aerobic (Becton Dickinson) and FAN Aerobic (Organon Teknika) media for recovery of fungi in general and in case of mixed bacterial/fungal septicemia. The results show that the BACTEC system detects nearly all enrolled microorganisms significantly faster than the BacT/ALERT; the anaerobic vial contributes to the detection of anaerobes and facultative anaerobes and, in the case of BACTEC, shortens TTD; the Bactec Mycosis IC/F bottle shortens TTD of fungi.

Speculations on the microbiology laboratory of the future

Changes in the availability of skilled laboratory personnel, new technologies, and the financial environment will all influence the practice of diagnostic microbiology in the near and more distant future. Because of the special expertise needed for the accurate identification of anaerobic bacteria, the ability to diagnose anaerobic infections may decline as a consequence of these changes. Physicians should anticipate a difficult time in the years between the loss of expertise in traditional methods and development of reliable and accurate molecular assays.

Diagnostic methods current best practices and guidelines for isolation of bacteria and fungi in infective endocarditis

This article addresses the clinical need for accurate detection of bacteria and fungi that may cause infective endocarditis (IE). The pathophysiology of bacteremia during endocarditis is reviewed to provide an understanding of how current diagnostic methods may be used to determine the etiologic diagnosis. The critical contribution of microbiologic findings to the current clinical diagnostic criteria is emphasized. Finally, "best practices" recommendations are presented to optimize the likelihood of reaching a correct etiologic diagnosis while minimizing the number of "culture-negative" cases.

Use of anaerobically incubated media to increase yield of positive blood cultures in children

During a 3-year period we received 10024 blood samples for culture from pediatric patients. Overall 181 episodes of significant bacteremia were documented. During the study period we would have missed 35 (19%) of all significant episodes of pediatric bloodstream infections if we had not been using the anaerobically incubated blood bottle. Anaerobically incubated blood samples are also necessary in the pediatric population.

Clinical review: bacteremia caused by anaerobic bacteria in children

This review describes the microbiology, diagnosis and management of bacteremia caused by anaerobic bacteria in children. Bacteroides fragilis, Peptostreptococcus sp., Clostridium sp., and Fusobacterium sp. were the most common clinically significant anaerobic isolates. The strains of anaerobic organisms found depended, to a large extent, on the portal of entry and the underlying disease. Predisposing conditions include: malignant neoplasms, immunodeficiencies, chronic renal insufficiency, decubitus ulcers, perforation of viscus and appendicitis, and neonatal age. Organisms identical to those causing anaerobic bacteremia can often be recovered from other infected sites that may have served as a source of persistent bacteremia. When anaerobes resistant to penicillin are suspected or isolated, antimicrobial drugs such as clindamycin, chloramphenicol, metronidazole, cefoxitin, a carbapenem, or the combination of a beta-lactamase inhibitor and a penicillin should be administered. The early recognition of anaerobic bacteremia and administration of appropriate antimicrobial and surgical therapy play a significant role in preventing mortality and morbidity in pediatric patients.

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.

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.

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.