Development of o.a.s.i.s., a new automated blood culture system in which detection is based on measurement of bottle headspace pressure changes

Considerations in evaluating equipment-free blood culture bottles: A short protocol for use in low-resource settings

Use of equipment-free, “manual” blood cultures is still widespread in low-resource settings, as requirements for implementation of automated systems are often not met. Quality of manual blood culture bottles currently on the market, however, is usually unknown. An acceptable quality in terms of yield and speed of growth can be ensured by evaluating the bottles using simulated blood cultures. In these experiments, bottles from different systems are inoculated in parallel with blood and a known quantity of bacteria. Based on literature review and personal experiences, we propose a short and practical protocol for an efficient evaluation of manual blood culture bottles, aimed at research or reference laboratories in low-resource settings. Recommendations include: (1) practical equivalence of horse blood and human blood; (2) a diverse selection of 10 to 20 micro-organisms to be tested (both slow- and fast-growing reference organisms); (3) evaluation of both adult and pediatric bottle formulations and blood volumes; (4) a minimum sample size of 120 bottles per bottle type; (5) a formal assessment of usability. Different testing scenarios for increasing levels of reliability are provided, along with practical tools such as worksheets and surveys that can be used by laboratories wishing to evaluate manual blood culture bottles.

Innovative Methods of Rapid Bacterial Quantification and Applicability in Diagnostics and in Implant Materials Assessment

In recent years, a variety of new technologies have been proposed that allow rapid qualitative and quantitative microbiological analyses. In this paper we discuss the urgent needs for reliable and rapid microbiological analytical techniques in different applicative fields involving the research, production and medical application of implant materials, and the potential benefits derived from the use of new methods for rapid bacterial quantification. Current compendial methods are easy to perform and have gained confidence over their long period of use, but the supplemental use of new technologies could represent real breakthroughs whenever sensitive and rapid responses are urgently required and not met by the tests currently in use. Overall, the new microbiological methods require critical evaluation depending on their specific type of application and they may still not be thought of as totally substitutive, but they certainly exhibit considerable potential for different areas of biomaterials, as well as for advanced therapy medicinal and tissue engineering treatments.

Controlled Evaluation of the New BacT/Alert Virtuo Blood Culture System for Detection and Time to Detection of Bacteria and Yeasts

We compared the newly approved BacT/Alert Virtuo blood culture system to the BacT/Alert 3D system using 115 clinical bacterial and fungal isolates in 784 simulated blood culture bottles. The time to detection was reduced by roughly 20% in the Virtuo system (P< 0.0001) while the detection rate did not differ.

Management of fever in infants and children

There is no question that fever is a source of great consternation for parent and physician alike; however, it is impossible to predict with certainty the outcome of every febrile illness. Inherent in the words diagnostic impression is a degree of uncertainty. The only question remaining is how much uncertainty is in the best interest of the child. Physicians try to use the existing scientific data to best determine the prevalence of disease and outcome. At the same time, they must recognize the limitations of both the data and their ability to be generalized to every population. Everything clinicians do has risks and costs, which they must balance against the incidence of complications and the benefits of testing. To take away clinical judgment makes physicians technicians not clinicians.

Tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6 levels in febrile, young children with and without occult bacteremia

OBJECTIVE

To determine the utility of plasma levels of tumor necrosis factor-alpha (TNF), interleukin 1 beta (IL-1), and interleukin 6 (IL-6) in the prediction of occult bacteremia in febrile, young children.

STUDY DESIGN

Prospective, case-control study conducted in a large, urban, children's hospital emergency department. Eligibility criteria were: 0 to 36 months of age, febrile, nontoxic appearing, immunocompetent, no apparent bacterial source for fever on physical examination, and blood culture obtained. Additional blood, procured at the time of the blood culture, was analyzed by enzyme-linked immunosorbent assay for TNF, IL-1, and IL-6. Children with positive blood cultures for pathogenic bacteria served as cases. Two age-matched controls for each case were selected from the children with negative cultures.

RESULTS

Out of 1329 enrollees, 33 cases and 66 controls were evaluated. IL-6 levels were significantly higher for the cases than controls but with moderate overlap in their ranges. TNF and IL-1 levels were not significantly different between cases and controls. Height of fever, duration of fever, acute illness observation score, absolute band count, and white blood cell count were all much less predictive of bacteremia than either IL-6 or absolute neutrophil count (ANC). The optimum IL-6 threshold value had a sensitivity of 88%, a specificity of 70%, a positive predictive value (PPV) of 7.0%, a negative predictive value (NPV) of 99.6%, and an odds ratio (OR) of 16.7 (95% confidence interval [CI], 4.8-71.6). The optimum ANC threshold value had a sensitivity of 82%, a specificity of 74%, a PPV of 7.5%, a NPV of 99.4%, and an OR of 12.8 (95% CI, 3.2-59.7). The best predictor was a combination of IL-6 and ANC. It had a sensitivity of 100%, a specificity of 78%, a PPV of 10.4%, a NPV of 100%, and an OR which is undefined because of the 100% sensitivity (95% CI, 33.0-infinity). For comparison, a WBC >15 x 10(9) cells/L had a sensitivity of 48%, a specificity of 79%, a PPV of 5.5%, a NPV of 98.3%, and an OR of 3. 5 (95% CI, 1.1-10.7).

CONCLUSIONS

In febrile children 0 to 36 months of age, IL-6 levels may be helpful in the prediction of occult bacteremia, but TNF and IL-1 levels are not. IL-6 levels alone or notably when combined with an ANC were more predictive of occult bacteremia than traditional tests and clinical criteria. The wide range in the IL-6 values for cases and controls detracts from the precision of the findings. The lack of rapid processing and clinical availability of IL-6 assays hampers its present application. However, despite these drawbacks and given the poor ability of traditional clinical and laboratory criteria to predict occult bacteremia, these results suggest a possible future role for IL-6 in predicting occult bacteremia when rapid assays become available.

Improved recovery of antibiotic-stressed microorganisms on inclusion of saponin in aerobic blood culture media

The recovery rates and times to detection of microorganisms isolated from two similar blood culture media, one containing saponin, were compared. A total of 2117 blood cultures were analysed in a prototype automated blood culture system. Significantly more gram-positive organisms (P<0.05) and gram-negative organisms (P<0.05), including Enterobacteriaceae (P<0.05) were recovered from the lytic medium. Average time to detection in the lytic medium was 15.8 h, compared to 22.7 h in the other medium (P<0.001). The improved recovery of microorganisms was most pronounced in blood samples obtained from patients being treated with antibiotics at the time of venesection. In vitro experiments on antibiotic affected bacteria confirmed the protective effect of saponin.

Microbiological and clinical aspects of infection associated with Stenotrophomonas maltophilia

The gram-negative bacterium Stenotrophomonas maltophilia is increasingly recognized as an important cause of nosocomial infection. Infection occurs principally, but not exclusively, in debilitated and immunosuppressed individuals. Management of S. maltophilia-associated infection is problematic because many strains of the bacterium manifest resistance to multiple antibiotics. These difficulties are compounded by methodological problems in in vitro susceptibility testing for which there are, as yet, no formal guidelines. Despite its acknowledged importance as a nosocomial pathogen, little is known of the epidemiology of S. maltophilia, and although it is considered an environmental bacterium, its sources and reservoirs are often not readily apparent. Molecular typing systems may contribute to our knowledge of the epidemiology of S. maltophilia infection, thus allowing the development of strategies to interrupt the transmission of the bacterium in the hospital setting. Even less is known of pathogenic mechanisms and putative virulence factors involved in the natural history of S. maltophilia infection and this, coupled with difficulties in distinguishing colonization from true infection, has fostered the view that the bacterium is essentially nonpathogenic. This article aims to review the current taxonomic status of S. maltophilia, and it discusses the laboratory identification of the bacterium. The epidemiology of the organism is considered with particular reference to nosocomial outbreaks, several of which have been investigated by molecular typing techniques. Risk factors for acquisition of the bacterium are also reviewed, and the ever-expanding spectrum of clinical syndromes associated with S. maltophilia is surveyed. Antimicrobial resistance mechanisms, pitfalls in in vitro susceptibility testing, and therapy of S. maltophilia infections are also discussed.

Update on detection of bacteremia and fungemia

The presence of microorganisms in a patient's blood is a critical determinant of the severity of the patient's illness. Equally important, the laboratory isolation and identification of a microorganism present in blood determine the etiologic agent of infection, especially when the site of infection is localized and difficult to access. This review addresses the pathophysiology and clinical characteristics of bacteremia, fungemia, and sepsis; diagnostic strategies and critical factors in the detection of positive blood cultures; characteristics of manual and instrument approaches to bacteremia detection; approaches for isolating specific microorganisms associated with positive blood cultures; and rapid methods for the identification of microorganisms in blood cultures.

Use of prototype automated blood culture system and gas-liquid chromatography for the analysis of continuous ambulatory peritoneal dialysis associated infection

AIMS

(1) To compare the recovery of organisms from continuous ambulatory peritoneal dialysis (CAPD) effluent fluid obtained from patients with clinical evidence of peritonitis, with an automated system (AS) and the Septichek blood culture system; (2) to evaluate the times to detection of organisms with the two systems; (3) to identify anaerobes from CAPD samples by extended anaerobic culture and gas-liquid chromatography (GLC).

METHODS

168 CAPD effluent fluid samples were studied, representing 157 episodes of peritonitis in 97 patients. CAPD samples were inoculated into two AS bottles-one anaerobic, one aerobic-and a Septichek bottle; samples were also examined for cell count, Gram stain, and direct culture. Culture bottles were then subcultured onto various media, and any organisms isolated were identified. After routine culture, GLC was performed on culture fluid in the anaerobic AS and Septichek bottles. When volatile fatty acids were detected, the broths were cultured anaerobically on specialised medium for a further five days.

RESULTS

147 organisms were isolated from the 168 samples: 96 (57%) yielded growth of significant organisms by direct culture, as compared to 129 (76.8%) by both AS and Septichek. There was no significant difference in isolation rates between AS and Septichek, but time to detection was more rapid with the AS system (p < 0.002). GLC showed volatile fatty acid in 15 specimens; of these, 14 subsequently grew anaerobic organisms.

CONCLUSIONS

AS was comparable to Septichek for numbers of isolations. Speed to detection was faster with the AS, which may be an advantage in management of patients with CAPD peritonitis. GLC showed anaerobes in several cases which would not have been detected without prolonged anaerobic culture; thus anaerobic cultures are recommended for patients who are unresponsive to antimicrobials or who have evidence of bowel perforation.

Continuous quality improvement for introduction of automated blood culture instrument

Despite the critical nature and high cost of blood cultures, hospitals rely on manufacturers' test site data. As a result, in-hospital testing and compliance evaluation of newly acquired instruments are seldom done. The goal of this study was to apply a continuous quality improvement approach and to develop assessment criteria for all stages from the purchase order, through the on-site instrument evaluation, to the compliance evaluation. Despite the introduction of an automated high-blood-volume instrument (BacT/Alert) in our hospital, 56% of adult patients had only one venipuncture and 89.5% had < or = 20 ml of total blood volume sampled. False positives were associated with overfilling of bottles. These problems occurred because the phlebotomists did not like to perform multiple venipunctures on ill patients; therefore, they were drawing 20 ml of blood from one venipuncture and splitting it between two bottles. Unknown to the staff, the vacuum in the bottles draws significantly more than 10 ml of blood; therefore, the first bottle in the set was frequently overfilled and the second bottle was frequently underfilled. A diagrammatic guideline for a new blood culture protocol based on two venipunctures, taken one immediately after the other, to inoculate three bottles was developed. Compliance evaluation demonstrated that within 1 month of starting the new protocol, 74% of patients had at least two or more venipunctures and 60% had > or = 30 ml of blood drawn per patient episode. This study demonstrates the need for continuous quality improvement, including compliance evaluation, to ensure that the potential benefits of newer blood culture technology are actually realized.