Comparison of lysis-centrifugation with a biphasic blood culture medium for the recovery of aerobic and facultatively anaerobic bacteria

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

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

Comparison of the lysis centrifugation method with the conventional blood culture method in cases of sepsis in a tertiary care hospital

Introduction:

Physicians and microbiologists have long recognized that the presence of living microorganisms in the blood of a patient carries with it considerable morbidity and mortality. Hence, blood cultures have become critically important and frequently performed test in clinical microbiology laboratories for diagnosis of sepsis.

Objectives:

To compare the conventional blood culture method with the lysis centrifugation method in cases of sepsis.

Materials and Methods:

Two hundred nonduplicate blood cultures from cases of sepsis were analyzed using two blood culture methods concurrently for recovery of bacteria from patients diagnosed clinically with sepsis – the conventional blood culture method using trypticase soy broth and the lysis centrifugation method using saponin by centrifuging at 3000 g for 30 minutes.

Results:

Overall bacteria recovered from 200 blood cultures were 17.5%. The conventional blood culture method had a higher yield of organisms, especially Gram positive cocci. The lysis centrifugation method was comparable with the former method with respect to Gram negative bacilli. The sensitivity of lysis centrifugation method in comparison to conventional blood culture method was 49.75% in this study, specificity was 98.21% and diagnostic accuracy was 89.5%. In almost every instance, the time required for detection of the growth was earlier by lysis centrifugation method, which was statistically significant. Contamination by lysis centrifugation was minimal, while that by conventional method was high. Time to growth by the lysis centrifugation method was highly significant (P value 0.000) as compared to time to growth by the conventional blood culture method.

Conclusion:

For the diagnosis of sepsis, combination of the lysis centrifugation method and the conventional blood culture method with trypticase soy broth or biphasic media is advocable, in order to achieve faster recovery and a better yield of microorganisms.

Effect of rinsing with povidone?iodine on bacteraemia due to scaling: a randomized-controlled trial

AIM

To investigate rinsing with povidone-iodine on bacteraemia caused by ultrasonic scaling.

MATERIAL AND METHODS

Sixty patients with gingivitis undertook a randomized, placebo-controlled trial in which 30 rinsed with 0.9% saline and 30 with 7.5% povidone-iodine for 2 min. before ultrasonic scaling of FDI teeth 31-35. Blood samples before and after 30 s and 2 min. of scaling were cultured by lysocentrifugation.

RESULTS

Oral bacteraemia occurred in 33.3% of the saline group and 10% of the povidone-iodine group. Regression analysis showed that rinsing with povidone-iodine was approximately 80% more effective than rinsing with saline in reducing the occurrence of bacteraemia, with a statistically significant odds ratio (OR) of 0.189 (95% confidence intervals, OR=0.043-0.827). There were 24 oral bacterial isolates in the saline group and 3 in the povidone-iodine group. Viridans streptococci comprised 11 of the isolates in the saline group and none in the povidone-iodine group. Bacteraemia magnitude was 0.1 colony-forming units/ml in the povidone-iodine subjects and 0.1-0.7 CFU/ml in the saline group.

CONCLUSIONS

Rinsing with 7.5% povidone-iodine reduced the incidence and magnitude of bacteraemia and eliminated viridans streptococci from such bacteraemia. Povidone-iodine rinsing may be helpful for ultrasonic scaling of gingivitis patients at risk of infective endocarditis.

A retrospective investigation of advanced periodontal disease as a risk factor for septicemia in hematopoietic stem cell and bone marrow transplant recipients

OBJECTIVE

Septicemia is a cause of death in hematopoietic stem cell transplant (HSCT) recipients. Extraction of teeth with advanced periodontitis has been advocated before HSCT to prevent septicemia in myeloablated hosts. The primary aim of the present study was to determine impact of chronic periodontitis, as measured by radiographic alveolar bone loss, on septicemia and transplant mortality.

STUDY DESIGN

A retrospective design was used to study 77 subjects who received pretransplant dental evaluation, panoramic radiography, and full myeloablative allogeneic HSCT to treat hematologic malignancies. Radiographic crestal alveolar bone loss was measured with a Schei ruler on all teeth. Microorganisms isolated from positive blood cultures within the first 100 days after transplant were categorized as of likely origin from periodontal, oral, or any body sites. Spearman correlation and logistic regression analysis assessed associations between positive blood cultures, mean subject whole-mouth percent radiographic crestal alveolar bone loss, and 100-day survival.

RESULTS

Radiographic crestal alveolar bone loss per study subject averaged 13% +/- 7%, with 18.2% exhibiting bone loss of 20% or greater. During the initial 100 days after transplant, 63.6% subjects yielded septicemia-associated positive blood cultures, with Staphylococcus epidermidis, Streptococcus mitis, Enterococcus faecalis, Streptococcus sanguis, Staphylococcus aureus, and Escherichia coli as the most common isolates recovered. No statistically significant associations were found between mean subject radiographic alveolar bone loss and septicemia of likely periodontal or oral origin.

CONCLUSION

In this preliminary study, no relationship was found between radiographic periodontal status and septicemia or mortality within the initial 100 days after transplant. A larger-sized, prospective study is warranted to further delineate the risk of septicemia from periodontal and other oral diseases in immunocompromised 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.

Clinical comparison of BACTEC 9240 plus aerobic/F resin bottles and the isolator aerobic culture system for detection of bloodstream infections

The Plus Aerobic/F resin bottle of the BACTEC 9240 automated blood culture system (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.) was compared with aerobic culture of the Isolator system (Wampole Laboratories, Cranbury, N.J.) for the detection of bloodstream microorganisms from 6,145 blood cultures collected from adult patients with suspected septicemia. The BACTEC resin bottles were incubated for 7 days, and the sediment from the Isolator tube was inoculated to sheep blood and chocolate agars which were incubated for 72 h and to inhibitory mold, brain heart infusion, and Sabouraud agars which were incubated for 21 days. A total of 622 microorganisms were recovered from 583 blood cultures. The BACTEC resin bottle recovered statistically significantly more pathogens overall than the Isolator system (P = 0.0006). When individual pathogens isolated from either system for a 7-day study period were assessed, it was determined that the BACTEC resin bottle detected statistically significantly more isolates of Staphylococcus aureus (P = 0.0113) and coagulase-negative Staphylococcus spp. (P = 0.0029) than the Isolator system. The BACTEC resin bottle also detected statistically significantly more bloodstream infections (septic episodes) caused by coagulase-negative Staphylococcus spp. (P = 0.0146). The Isolator system recovered statistically significantly more contaminants overall (P < 0.0001), and among this group of microorganisms, recovered statistically significantly more Bacillus spp. (P < 0.0001), coagulase-negative Staphylococcus spp. (P < 0.0001), and viridans group Streptococcus spp. (P = 0.0156). The Isolator system detected statistically significantly more isolates of Histoplasma capsulatum (P = 0.004), but all of these isolates were detected at > or = 7 days of incubation of fungal plates, i.e., after the system to system comparison study period (7 days). In blood culture sets which produced growth of the same pathogen in both systems, there was a statistically significant difference in median time to detection for all pathogens combined favoring the BACTEC resin bottle over the Isolator tube (P < 0.05). When assessing individual microorganisms, the median times for detection of S. aureus, Enterococcus spp., and Pseudomonas spp. were all statistically significantly less for the BACTEC system (P < 0.05). The BACTEC instrument had 79 (1.3%) false positive signals. The BACTEC system required less processing time than the Isolator system and eliminates the hands-on time for detection of positive cultures required with the Isolator system.

Yield of positive blood cultures in pediatric oncology patients by a new method of blood culture collection

BACKGROUND

The optimal number of blood cultures and the volume of blood for pediatric blood cultures have not been defined. In 1990 such criteria were established at our institution. We retrospectively reviewed records of all pediatric oncology patients who were admitted for febrile episodes in 1989 and in 1991 and 1992 to determine whether there was an increase in the detection of bacteremia and fungemia.

METHODS

Blood was drawn via venipuncture and central intravascular catheters and inoculated into the designated blood culture bottles. Each patient had a minimum of two separate blood draws, i.e. two separate cultures; the volume was determined by the patient's weight. In all cases < 1% of the patient's blood volume was drawn per culture. Patients' records were reviewed regarding type of malignancy, chemotherapy and neutropenia.

RESULTS

The rate of bacteremic patients increased from 12% (13 of 113) in 1989 to 22% (27 of 123) in 1991. This increase continued through 1992 with 23% (27 of 118) of patients having positive blood cultures. Gram-positive bacteria predominated throughout the study period.

CONCLUSIONS

Although factors such as more aggressive chemotherapy or a different spectrum of malignant diseases may contribute to the statistically significant increase in identification of bacteremic patients, a standardized method of blood culture collection is merited. The consistent volumes of blood per culture and the minimum of two cultures per febrile episode follow the principles of blood culture collection established for adults. The same principles should apply to pediatric patients.

Clinical comparison of isolator, Septi-Chek, nonvented tryptic soy broth, and direct agar plating combined with thioglycolate broth for diagnosing spontaneous bacterial peritonitis

Spontaneous bacterial peritonitis is a life-threatening complication of cirrhotic ascites. Optimal patient management depends on the isolation of the causal organism from ascitic fluid. To evaluate culture techniques for the diagnosis of spontaneous bacterial peritonitis, we prospectively compared three blood culture system, the Isolator system, a lysis-centrifugation system, the Septi-Chek system, a biphasic culture system, and a nonvented tryptic soy broth system, all inoculated at the bedside, and our standard method of direct inoculation of specimens after transport to the laboratory onto agar plates and into thioglycolate broth. The results showed that the Septi-Chek and nonvented tryptic soy broth systems each recovered statistically significantly more pathogens than either the Isolator system (P = 0.0084) or the standard method (P = 0.00098). The Isolator system recovered more pathogens than the standard plate method, but this difference was not statistically significant. Both the Isolator system and the standard plate method recovered more contaminating microorganisms than the Septi-Chek or nonvented tryptic soy broth system. The Isolator system required the most processing time compared with the processing times required by any other method.

Clinical comparison of difco ESP, Wampole isolator, and Becton Dickinson Septi-Chek aerobic blood culturing systems

The ESP 80A aerobic blood culture of the ESP automated blood culture system (Difco Laboratories. Detroit, Mich.) was compared with two manual aerobic blood culture systems, the Isolator (Wampole Laboratories, Cranbury, N.J.) and the Septi-Chek (Becton Dickinson, Cockeysville, Md.) systems, for the detection of bloodstream microorganisms from 5,845 blood samples for culture collected from adult patients with suspected septicemia. The bottles were incubated for 7 days, and the sediment from the Isolator tube was inoculated onto solid medium and this medium was incubated for 72 h. A total of 609 microorganisms were recovered from 546 blood cultures. There was no statistically significant difference in the total recovery of microorganisms for the ESP 80A system when compared with that for the Septi-Chek system (P = 0.083); however, the Isolator system recovered significantly more microorganisms overall than either the ESP 80A (P < 0.001) or the Septi-Chek (P < 0.001) system. When assessing individual probable pathogens, the Isolator system detected statistically significantly more Staphylococcus aureus and Candida spp. than either the ESP 80A or the Septi-Chek system (P < 0.05). Similarly, the Isolator system detected statistically significantly more bloodstream infections (septic episodes) caused by S. aureus and Candida spp. than either the ESP 80A or the Septi-Chek system (P < 0.05). In blood culture sets which produced growth of the same probable pathogens in the ESP 80A and the Isolator systems, there was no statistically significant difference in the median times to detection for all pathogens combined (P = 0.067). However, a similar comparison showed the Isolator and the ESP 80A systems to have statistically significantly shorter median detection times for all pathogens combined (P < 0.001) when they were independently compared with the Septi-Chek system. The ESP 80A system had 29 (0.5%) false-positive signals. The ESP system required less processing time than the Isolator system and eliminates the hands-on time for the detection of positive cultures required by the manual systems.

Clinical comparison of the isolator and BacT/Alert aerobic blood culture systems

The performance characteristics of the Isolator (Wampole Laboratories, Cranbury, N.J.) and the BacT/Alert (Organon Teknika Corporation, Durham, N.C.) aerobic blood culture systems were compared for 6,009 blood culture sets obtained from patients with suspected bloodstream infections. The BacT/Alert aerobic bottle [BTA(O2)] was continuously agitated while it was incubated in 5% CO2 at 36 degrees C; culture plates prepared from the Isolator tube [I(O2)] were incubated in 5% CO2 at 37 degrees C. From 394 blood cultures, 416 clinically significant isolates of bacteria and yeasts were recovered. The overall yields for BTA(O2) and I(O2) were not significantly different (319 versus 336; P = 0.20). I(O2) recovered significantly more staphylococcus (P < 0.05) and yeast isolates (P < 0.01). BTA(O2) recovered significantly more aerobic and facultatively anaerobic gram-negative bacilli (P < 0.05). In blood culture sets which produced growth of the same organisms in both the BTA(O2) and I(O2) systems, the BTA(O2) system detected growth sooner, but more rapid identification was possible with the I(O2) system by virtue of earlier isolation of colonies on solid media.

Evaluation and comparison of different blood culture techniques for bacteriological isolation of Salmonella typhi and Brucella abortus

An experimental study was carried out to evaluate and compare various noncommercial methods of blood culture for the isolation of Salmonella typhi and Brucella abortus from fresh human blood samples that had been artificially inoculated with 1 to 50 microorganisms per ml of blood. The methods compared included the Ruiz-Castañeda blood culture, broth blood culture, leukocyte lysis and direct plating on agar (WBL-P), leukocyte lysis and filtration, Ficoll-Hypaque centrifugation and filtration, Ficoll-Hypaque centrifugation, and Ficoll-Hypaque centrifugation and leukocyte lysis methods. Results with the WBL-P technique showed that S. typhi was isolated in 18 h, and its recovery rate was 36.6% (calculated from the number of CFU recovered per milliliter versus the number inoculated). B. abortus was isolated in 48 h by the same technique, and its recovery rate was 48.8%. The isolation times for the other blood culture techniques were between 36 and 44 h for S. typhi and 66 h for B. abortus. The techniques which relied on filtering systems for the recovery of S. typhi and B. abortus performed poorly. The WBL-P technique for the isolation of S. typhi and B. abortus is faster than the other methods tested.

Clinical comparison of isolator and thiol broth with ESP aerobic and anaerobic bottles for recovery of pathogens from blood

The recovery of pathogens and the speed of their detection were determined for our conventional blood culture system (an Isolator [Wampole] and a 100-ml Thiol bottle [Difco]) compared with automated ESP aerobic and anaerobic bottles (80 ml each; Difco). Each of the four culture devices was inoculated with approximately 10 ml of blood from symptomatic patients weighing more than 80 lb (ca. 36 kg). From 7,070 sets of cultures for 2,841 patients, 607 clinically significant isolates were recovered: 456 (75.1%) from the Isolator, 353 (58.2%) from Thiol, 377 (62.1%) from ESP aerobic bottles, and 346 (57.0%) from ESP anaerobic bottles. Of the 607 isolates, 149 (24.5%) were detected only with the conventional system (Isolator and/or Thiol), and 65 (10.7%) were detected only with the ESP two-bottle system (P < 0.001). Our conventional system allowed for detection of significantly more isolates of members of the family Enterobacteriaceae (P < 0.001), Staphylococcus aureus (P < 0.01), Staphylococcus spp. (coagulase-negative) (P < 0.01), and Enterococcus spp. (P < 0.05), and ESP facilitated detection of significantly more isolates of S. pneumoniae (P < 0.01). When all four devices in a culture set were positive for the same isolate, no microbial species or group was detected significantly earlier ( > or = 24 h) by either blood culture system. The Isolator contamination rate (4.8%) was > or = 6 times the rate for any of the bottles. Of pathogens detected by the Isolator, 50% were recovered in counts of < or = 1.0 CFU/ml and 18% were recovered only as a single colony. The ESP system offered an automated, less labor-intensive blood culture system for which routine subcultures were not required, but the important considerations of culturing large volumes of blood and of obtaining at least two sets from each patient in our population were reemphasized.

Evaluation of two commercial blood culture media for the detection of blood-borne pathogens

To determine their ability to detect blood-borne pathogens, the blood culture media BCB Release (Becton Dickinson, USA) and Signal (Oxoid, UK) were evaluated on a total of 5,122 blood culture sets. Each of the two bottles was inoculated with an equal amount of blood from 2,262 patients at bedside (2.3 cultures per patient). In the laboratory, agar-coated paddles were attached to the BCB Release bottles and the Signal device was mounted onto the Signal bottles. Both systems were incubated at 35 degrees C for seven days. A total of 608 (11.9%) sets were positive, from which 549 pathogenic microorganisms could be isolated. These could be grown significantly (p < 0.0001) more often from the BCB Release broth (n = 483) than from the Signal system (n = 384). Mainly staphylococci, Escherichia coli and yeasts were isolated more often from the BCB Release, anaerobes were more often detected from the Oxoid Signal. The time to positivity was significantly shorter (p < 0.0001) with the BCB Release. The Signal system proved a valuable complement to the BCB Release broth.

Incidence and clinical significance of positive blood cultures in febrile episodes of patients with hematological malignancies

The characteristics of 554 febrile episodes in 126 patients with a hematological malignancy over a 6-year period (1985-90) were reviewed in order to study the current incidence and clinical significance of blood culture positivity. An infection was documented microbiologically in 28% and clinically in 30% of the episodes. Blood cultures were positive in 19% of the febrile episodes. The rate of blood culture positivity was unrelated to the type of hematological malignancy, to neutropenia and to the presence of infection foci. 21% (26/126) of the patients died of sepsis-related causes. Sepsis-related death occurred in 23% of the blood culture positive febrile episodes, with a median survival time of 2 days. Infection prophylaxis did not reduce either the rate of blood culture positivity or the rate of sepsis-related deaths. Thus, the small proportion of febrile episodes whose fever etiology could be established by blood culture represented 'the tip of the iceberg', i.e. rapidly lethal septic infections with a high mortality rate. This fatality could neither be predicted by a search for infection foci nor prevented by infection prophylaxis.

Methods used in the United Kingdom for the culture of micro-organisms from blood

AIMS

To survey blood culture methods in use in the United Kingdom.

METHODS

A questionnaire was distributed to the 415 United Kingdom laboratories participating in the clinical bacteriology subscheme of the UK National External Quality Assessment Scheme for Microbiology.

RESULTS

Two hundred and eighty seven laboratories completed the questionnaire. The responses indicated wide variations in methods used including considerable differences among laboratories using the same basic methods. The most widely used techniques were the Bactec and conventional broth systems.

CONCLUSIONS

Although many published comparisons have failed to show that any basic method is outstandingly successful in the isolation of all organisms, there is evidence that several factors can contribute to good performance. In some laboratories suboptimal conditions were in use. The variations in technique probably reflect differences in practical suitability of a system for any particular laboratory, costs, and personal preferences.

Evaluation of the new improved BHI-lysis blood culture medium for the BCB Roche system

The new BHI-lysis blood culture medium for the BCB system (BCB release, Hoffmann-La Roche), which lyses blood cells, was compared with the BHI-S broth of the same BCB system and the Signal system (Oxoid). A total of 2394 sets consisting of three bottles were each inoculated with 7 ml of blood at the bedside. In the laboratory agar-coated paddles were attached to the BHI-lysis and the BHI-S bottles, and the Signal device was mounted onto the Oxoid bottle. All systems were incubated at 35 degrees C for seven days. Of the 309 (13%) positive sets, 73 (3%) were contaminated and in 242 (10%) sets a total of 250 pathogenic microorganisms were isolated. These could be grown significantly more often from the BHI-lysis bottle (n = 213) than from either the BHI-S (n = 189) or Signal bottle (n = 176). No significant differences in the time needed to achieve a positive result was noted between the BHI-lysis and BHI-S bottles, but comparison of the BHI-lysis and Signal bottles revealed that overall pathogens were detected earlier significantly more often with the BHI-lysis bottle. In view of the good performance of blood culture broths containing lysing agents, their wider use is warranted in future.

Prospective evaluation of the risk of bacteremia associated with transesophageal echocardiography

BACKGROUND

Transient bacteremia may lead to endocarditis in patients with significant valvular lesions.

METHODS AND RESULTS

Because transesophageal echocardiography selects a patient population with a high prevalence of valvular lesions, we prospectively evaluated the risk of transient bacteremia associated with transesophageal echocardiography in 49 patients. Blood cultures were obtained immediately before transesophageal echocardiography and at 5, 10, and 20 minutes after the start of the procedure. For each culture, 30 ml venous blood was obtained and 10 ml was inoculated into each of an Isolator tube, Septi-chek bottle, and a nonvented Trypticase soy broth bottle. Broth cultures were incubated for 14 days. Blood from the Isolator tube was plated onto appropriate media for recovery of bacteria and fungi. Two patients were excluded from analysis because the final two sets of blood cultures could not be obtained. Among the remaining 47 study patients, two preprocedure control blood cultures were positive, and two of 141 subsequent cultures were positive. All isolates were considered contaminants. Thus, we found no significant bacteremia due to pathogenic oral flora during transesophageal echocardiography (0%; 95% CI, 0.0-7.5%).

CONCLUSIONS

Although recommendations for antimicrobial prophylaxis for transesophageal echocardiography should be individualized for each patient, many patients may not require antimicrobial prophylaxis.

Clinical comparison of the recoveries of bloodstream pathogens in Septi-Chek brain heart infusion broth with saponin, Septi-Chek tryptic soy broth, and the isolator lysis-centrifugation system

The recoveries of microorganisms in the Septi-Chek biphasic tryptic soy broth (TSB) and Isolator blood culturing systems were compared with the recovery in Septi-Chek biphasic brain heart infusion broth supplemented with the lytic agent saponin (L-BHIB; Roche Diagnostics, Division of Hoffmann-La Roche Inc.). A total of 5,096 TSB-L-BHIB blood culture sets and 1,778 Isolator-L-BHIB sets were evaluated. There were 435 pathogenic organisms recovered in 413 (8.1%) of the TSB-L-BHIB cultures, with 348 organisms in the TSB bottles and 370 in the L-BHIB bottles (P less than 0.05). Significantly more yeast isolates were recovered in the L-BHIB system (P less than 0.01). Terminal subculture of the L-BHIB system was required to detect 13 clinically significant organisms. Significantly more organisms were recovered in the L-BHIB bottles than with the Isolator system (P less than 0.001), including Torulopsis glabrata, coagulase-negative staphylococci, and Pseudomonas species. The time required for detection of all major groups of organisms was the same in both comparisons. However, detection of microbial growth in the L-BHIB bottles required macroscopic inspection of the attached agar slide unit and the use of terminal subcultures after 7 days of incubation. The primary advantage of the biphasic L-BHIB system when compared with either the biphasic TSB system or the Isolator system was improved recovery of fungi.

Comparison of the lysis-centrifugation and agitated biphasic blood culture systems for detection of fungemia

Although the detection of fungemia has been improved by the use of vented or biphasic blood culture bottles, the best recovery and earliest detection have been reported in the Isolator lysis-centrifugation system. It was recently demonstrated that improved detection of both bacteria and fungi was accomplished by mechanically agitating blood culture bottles for the first 24 h of incubation. In this study the detection of fungemia by use of the Isolator system was compared with that of an agitated biphasic system. A total of 182 fungi were isolated from blood specimens inoculated into both culture systems. No difference in the overall recovery of fungi or individual species of yeasts was observed between the two systems. However, all seven isolates of Histoplasma capsulatum were recovered in the Isolator system only. The time required to detect fungemia with each of the two systems was also compared. No statistically significant difference was observed. From the data collected during this 18-month study, it can be concluded that the overall recovery and time of detection of yeasts are equivalent in the lysis-centrifugation system and the agitated biphasic blood culture system. The lysis-centrifugation system is still superior for the detection of filamentous fungi such as H. capsulatum.

Antimicrobial therapy of septicemic patients in intensive care units before and after blood culture reporting

68 cases of positive blood cultures from 54 intensive care unit (ICU) patients were analyzed retrospectively. The empiric antimicrobial therapy was correct in 65% of the cases as judged by the species and sensitivity of the blood culture isolate. After initial Gram-staining results were known, coverage increased to 77%. After the final blood culture results the coverage was still only 81%. The bacteremia-related mortality was 13%. Although there was no significant difference between the occurrence of bacteremia-related and non-bacteremia-related deaths either in patients with correct or non-optimal empiric treatment, this study emphasizes the need for better utilization of culture reporting. A considerable part of the final blood culture results went unnoticed by the ICU physicians which stresses the importance of good communication between the laboratory and wards.

Quantitative aspects of septicemia

For years, quantitative blood cultures found only limited use as aids in the diagnosis and management of septic patients because the available methods were cumbersome, labor intensive, and practical only for relatively small volumes of blood. The development and subsequent commercial availability of lysis-centrifugation direct plating methods for blood cultures have addressed many of the shortcomings of the older methods. The lysis-centrifugation method has demonstrated good performance relative to broth-based blood culture methods. As a result, quantitative blood cultures have found widespread use in clinical microbiology laboratories. Most episodes of clinical significant bacteremia in adults are characterized by low numbers of bacteria per milliliter of blood. In children, the magnitude of bacteremia is generally much higher, with the highest numbers of bacteria found in the blood of septic neonates. The magnitude of bacteremia correlates with the severity of disease in children and with mortality rates in adults, but other factors play more important roles in determining the patient's outcome. Serial quantitative blood cultures have been used to monitor the in vivo efficacy of antibiotic therapy in patients with slowly resolving sepsis, such as disseminated Mycobacterium avium-M. intracellulare complex infections. Quantitative blood culture methods were used in early studies of bacterial endocarditis, and the results significantly contributed to our understanding of the pathophysiology of this disease. Comparison of paired quantitative blood cultures obtained from a peripheral vein and the central venous catheter has been used to help identify patients with catheter-related sepsis and is the only method that does not require removal of the catheter to establish the diagnosis. Quantitation of bacteria in the blood can also help distinguish contaminated from truly positive blood cultures; however, no quantitative criteria can invariably differentiate contamination from bacteremia.

Effect of delay in processing on lysis-centrifugation blood culture results from marrow transplant patients

The effect of delay in processing on results of lysis-centrifugation (LC; Isolator) blood cultures was assessed in 4,577 paired blood specimens. Blood specimens were obtained at all hours from 384 febrile marrow transplant patients with indwelling venous catheters and were processed by the LC technique and by a conventional two-bottle method. Most patients (84%) were receiving broad-spectrum antibiotics at the time of blood culture. Specimens were delivered to the laboratory, where Isolator tubes were held at 35 degrees C and processed in batches between 0700 and 1730 h daily. This procedure resulted in a delay beyond the manufacturer-suggested processing time of less than 8 h for 1,853 (42%) of the LC cultures. There was no overall difference in the recovery of organisms present in LC cultures processed after being held for 8 to 24 h compared with the conventional two-bottle method. LC methodology had shorter time to detection than the conventional method for detection of Candida spp. and Pseudomonas spp. (P less than 0.05). However, time to detection for Streptococcus spp. and members of the family Enterobacteriaceae, responsible for 16.3% of total isolates, was prolonged significantly by delay in processing when compared with the conventional two-bottle method (P less than 0.01). Results of this study support the recommendation of the manufacturer for processing of Isolator tubes within 8 h or less. Although one can safely delay processing beyond 8 h in terms of total recovery of organisms, such delays were associated with longer time to detection for certain important potentially pathogenic organisms which accounted for a sizeable proportion of blood culture isolates from marrow transplant patients.

Evaluation of the lysis-centrifugation system for culturing dialysates from continuous ambulatory peritoneal dialysis patients with peritonitis

Recovery of organisms from continuous ambulatory peritoneal dialysis (CAPD) patients with peritonitis presents special problems to the laboratory. The Isolator (Dupont Co, Wilmington, DE), based on lysis and centrifugation, is generally used for the recovery of blood isolates. This study determined the efficacy of the Isolator relative to the Bactec System (Johnston Laboratories, Inc, Towson, MD) for the culture of dialysates from CAPD patients with peritonitis. On the basis of clinical criteria, 31 episodes of peritonitis were included for our study. Dialysate was inoculated into an Isolator and Bactec 6B and 7D bottles. A causative agent was isolated by the Isolator in 29 of 31 episodes, by the Bactec in 29 of 31, and by one or both techniques in 30 of 31 episodes (overall sensitivity 97%). The Isolator failed to detect a Pseudomonas luteola and the Bactec failed to detect a coagulase-negative staphylococcus. Coagulase-positive and negative staphylococci represented 58.1% of the isolates. The Isolator detected 21.4% (six of 28) of the isolates 24 to 72 hours earlier than the Bactec; the Bactec was faster in this regard in 3.6% (one of 28). Time to positivity for the remaining 21 cultures was the same in both systems. Isolate identification and antimicrobial sensitivity was available 24 hours earlier using the Isolator in 96.4% (27 of 28). The Isolator was more rapid and as sensitive as the Bactec system in detecting causative organisms of peritonitis in CAPD patients.

New developments in medical microbiology: computer-assisted diagnosis and automated instruments

Time and accuracy required for diagnosis are two of the most important factors in medical microbiology. Computer-assisted diagnosis is one tool to overcome these problems. The software of such systems, much more than the hardware, is of utmost importance and both have to fulfill several items. 1) High flexibility and integration within the already existing working schemes of the laboratory. 2) Terminals in every laboratory. 3) High speed of calculation. 4) Online data transfer from automated instruments. 5) External terminals on intensive care units. 6) Epidemiological and etiopathological investigations have to be possible at any time. In the laboratory the burden of simple, repeating tasks is diminished, inquiries can be made in a minute and precise information about the epidemiological situation can be gained within a few hours. Thus, calculated antimicrobial therapy depending on the incidence of certain pathogens in given specimens in different departments is possible. In the case of fast-growing bacteria, preliminary reports, including susceptibility testing available within the first 24 h, are possible and will be of great help to the clinician in monitoring the calculated antimicrobial regimen. External terminals will allow continuous flow of data from the laboratory to wards and vice versa.

Lysis centrifugation and slide blood culture systems for diagnosis of bacteremia in immunocompromised patients

Compared with a slide blood culture system, a lysis centrifugation system detected significantly more positive blood cultures and more episodes of bacteremia in immunocompromised patients (even when on antibiotics), while giving results more rapidly and even at significantly lower CFUs. However, it had a high contamination rate and did not detect Pseudomonas aeruginosa as often. Use of the two systems together is recommended for diagnosing bacteremia early in immunocompromised patients.

Effect of agitation and frequent subculturing on recovery of aerobic and facultative pathogens by Roche Septi-Chek and BACTEC blood culture systems

The positivity rate and time to recovery of pathogens were compared in Roche Septi-Chek (RSC-TSB) and BACTEC radiometric systems on 3,539 paired blood cultures. Both systems were steadily agitated, with frequent subculturing or processing of the RSC-TSB agar slides and BACTEC bottles, respectively, during the first 24 h of incubation. The RSC-TSB system recovered 249 pathogens (7.0% positivity rate), compared with 234 (6.6% positivity rate) isolates recovered from BACTEC. For the most common isolates, Staphylococcus aureus and the Enterobacteriaceae, the median time to detection was 15.8 h for BACTEC and 18.6 h for the RSC-TSB system. No statistically significant difference was observed in recovery of organisms from the two systems, except for S. aureus (P less than 0.05). In the RSC-TSB system, 42% of S. aureus, 58% of the Enterobacteriaceae, and 45% of Pseudomonas aeruginosa isolates had sufficient growth on the agar slant to allow performance of rapid standardized identification and susceptibility studies. In comparison with other studies using static incubation, it appears that agitation and frequent subculturing of the RSC-TSB system during the first 24 h of incubation decreased the time to detection for the majority of significant blood culture isolates.

Distribution of bacteria and yeasts within the 10-ml Isolator during the processing of seeded blood samples

Forty-five organisms consisting of stock cultures and clinical isolates of bacteria and yeast were separately inoculated into outdated blood bank blood to achieve a concentration of approximately 100 CFU/ml. Blood with each organism was introduced into groups of four Isolators (E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.), which were then processed according to the Isostat instructions of the manufacturer. The supernatant, sediment, and wash (material removed from the surface of the slanted stopper after sediment removal) were inoculated onto 5% sheep blood agar plates. Cultures were incubated aerobically (5 to 10% CO2) at 35 degrees C for 48 to 72 h. From the 180 Isolators, the mean recovery was 6% (range, 0 to 48%) for the supernatant, 87% (range, 47 to 98%) for the sediment, and 8% (range, 3 to 23%) for the wash. Neither variation among technologists nor intentional misalignment of additional Isolators in the centrifuge could explain all of the losses of microorganisms from the sediment. The manual nature of the Isolator procedure, which led to the loss of significant amounts of organisms from the sediment, may help to explain false-negative Isolator results obtained from blood of patients, particularly when small numbers of pathogens are present.