Clinical comparison of Sentinel, a novel blood culture system, with radiometric Bactec 460 and Isolator 10 in the detection of streptococcal and anaerobic bacteraemias.

AIMS: To compare the performance of the Sentinel blood culture system with two other systems for the recovery of streptococci and anaerobes. METHODS: Blood cultures were taken from 55 patients one to two minutes after dental extraction. The samples were tested by the radiometric Bactec 460; the Isolator 10, which works by lysis centrifugation; and Sentinel, a fully automated system, which detects bacterial growth by changes in the voltage between two electrodes in the media. Positive samples were subcultured and streptococci and anaerobes were further identified. Terminal subcultures were performed on all negative samples. RESULTS: Sentinel was comparable with Bactec, with Sentinel recovering 20 streptococci and 14 anaerobes; Bactec isolated 26 streptococci and 15 anaerobes. The recovery of Streptococcus sanguis was significantly better from Bactec than Sentinel. The Isolator 10 recovered significantly fewer streptococci and anaerobes than either Bactec or Sentinel. Sentinel was noticeably quicker in detecting anaerobes than Bactec 460. However, there was no comparable difference with streptococci. Contaminants were recovered from 10% of Isolator 10, 2.7% of Bactec, and 7.2% of Sentinel bottles. CONCLUSIONS: Sentinel and Bactec 460 were broadly comparable in the detection of viridans streptococci and oral anaerobes, and both systems were significantly better than the Isolator 10. However, the prototype Sentinel, was significantly poorer than Bactec for the recovery of S sanguis.     

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 °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.     

Comparison of radiometric and gas capture system for blood cultures.

A single bottle blood culture system that detects the gas produced by micro-organisms from substrates in a specially formulated medium was compared with the Bactec radiometric system. A total of 725 blood samples collected from patients with suspected bacteraemia yielded 75 clinically important isolates. Fifty five (73%) of these cultures were detected by both methods, 16 (21%) by only the Bactec system, and four (5%) by only the Oxoid system. No significant differences were found between the two systems after allowance was made for the different volume of sample inoculated into each system.     

Comparative evaluation of the oxoid signal and Roche Septi-Chek blood culture systems.

The Oxoid Signal blood culture system (Oxoid USA, Inc., Columbia, Md.) was compared with the Roche Septi-Chek system (Roche Diagnostics, Div. Hoffmann-La Roche Inc., Nutley, N.J.), with the latter consisting of a tryptic soy broth (R-TSB) bottle with an attached agar slide unit and a Columbia broth bottle. A total of 5,034 cultures with equal volumes of blood in each bottle were processed. Overall, more organisms were recovered in the R-TSB bottle than in the Signal bottle, with significantly more aerobic organisms (Pseudomonas spp., Acinetobacter spp., and yeasts) recovered in the R-TSB bottles and anaerobes and viridans group streptococci recovered in Signal bottles. Approximately equivalent numbers of organisms were recovered in the Signal and Columbia broth bottles. The times of detection were essentially identical with the three blood culture broth systems. During the study, 30.6% of the Signal bottles had a positive indicator of growth, of which 1,103 (71.7%) were false-positive cultures. Additionally, nonviable organisms resembling streptococci were observed in 13.7% of the Signal bottles that were Gram stained and in unioculated blood culture bottles. With appropriate modifications of the preparation of the media, the latter problem can be eliminated.     

Comparison of 2 systems of blood culture: Signal and Bactec

Two Bactec bottles (aerobic and anaerobic) and one single bottle Signal were used for detecting bacteremia in 405 patients (47 children and 358 adults). The two blood culture Signal and Bactec aerobic were continuous shaking for up to 24 hours. 10.3 p. cent of patients had positive cultures (62.3 p. cent Gram +, aero-anaerobic bacteria). Nine bacteremia were detected by only one system (4 for signal, 4 for Bactec) 77.1 p. cent of 83 strains were positive on the two systems together, but 7.2 p. cent only in the Bactec and 15.6 p. cent only in the Signal. The delay of growth give an advantage to the Bactec (67 p. cent in 24 hours). The advantages and the disadvantages of the two systems were analysed.     

Comparative evaluation of the BCB Roche and Oxoid Signal blood culture systems

The agar-slide blood culture system BCB Roche was compared with the Oxoid Signal blood culture system using 2,266 paired blood cultures. A total of 271 (12%) paired sets were culture-positive, including 222 (9.8%) yielding pathogens associated with septicemia and 50 (2.2%) yielding likely contaminants. In the recovery of the total 235 isolates considered as pathogens, the BCB Roche system yielded 202 (85.9%), the Oxoid Signal 211 (89.8%); 178 (75.7%) were cultured by both systems. There was no statistically significant difference between the two systems in their sensitivity, contamination-rate and detection time, except for gram-positive organisms, which were detected earlier by the Oxoid Signal system. Both systems performed well and were easy to handle.     

Experience of changing between signal and Bactec 9240 blood culture systems in a children's hospital.

AIM: To compare experience of positive blood cultures in successive years before and after changing from Signal (Unipath) to Bactec 9240 (Becton Dickinson) blood culture systems. METHODS: Analysis of data collected prospectively on 7967 Signal and 7062 Bactec blood culture sets. RESULTS: Significant growths occurred in 5.7% of Signal and 8.9% of Bactec cultures; 33.0% more significant isolates and 24.0% more episodes of bacteraemia were detected in the second year, following introduction of the Bactec system. Inpatient hospital activity increased by 8.2% between the first and second years, although the numbers of blood cultures received actually fell by 11.4%. There were striking increases in numbers of isolates of coagulase negative staphylococci (47.7%) and Enterobacteriaceae (56.8%) from Bactec cultures. Two anaerobic bacteraemias were detected in Signal blood cultures, whereas none was detected by the Bactec system, despite 12.1% of sets including an anaerobic bottle. Of significant positive cultures, 90.2% were detected within one day with the Bactec 9240, compared with only 50.0% of Signal cultures; 20.7% of significant positive Signal blood cultures were detected only on terminal subculture. Microorganisms that were not significant were isolated from 5.1% Signal and 3.8% Bactec cultures. CONCLUSIONS: Compared with the Signal system, the Bactec 9240 offers markedly more rapid and sensitive detection of bacteraemia, together with a lower rate of non-significant isolates. However, using a single PEDS PLUS/F bottle the few episodes of anaerobic bacteraemia that occur in children are likely to be missed.     

Comparative evaluation of Oxoid Signal and BACTEC radiometric blood culture systems for the detection of bacteremia and fungemia.

The Oxoid Signal (Oxoid U.S.A., Inc., Columbia, Md.) blood culture system is a newly described, innovative method for visually detecting growth of microorganisms (D. Sawney, S. Hinder, D. Swaine, and E.Y. Bridson, J. Clin. Pathol. 39:1259-1263, 1986). We did 5,999 paired comparisons of equal volumes (10 ml) of blood in the Oxoid Signal and BACTEC (Johnson Laboratories, Towson, Md.) radiometric blood culture systems at two university hospitals that use identical methods of obtaining and processing specimens. Overall, more microorganisms were detected in the BACTEC system (P less than 0.001), in particular, streptococci (P less than 0.01), fungi (P less than 0.001), and nonfermentative gram-negative rods, especially Acinetobacter species (P less than 0.001). Trends favoring the BACTEC system for detection of Pseudomonas aeruginosa, Haemophilus species, and Neisseria species were noted. There were no differences in the yield of staphylococci, members of the family Enterobacteriaceae, and anaerobic bacteria. When both systems detected sepsis, the BACTEC did so earlier (P less than 0.001). This advantage was most notable at 24 h (70% of BACTEC positives detected versus 48% of Oxoid positives). The proportion of positives detected after 48 h, however, was similar (BACTEC, 84%; Oxoid, 78%). Revisions in the Oxoid Signal system itself or in the processing of Oxoid bottles appear to be necessary to improve its performance in detecting certain microorganism groups, especially fungi.     

Comparison of conventional and single bottle system for blood cultures.

A single bottle blood culture system (Oxoid Signal system) was compared with a conventional two bottle subculturing system. A total of 2016 routine blood samples yielded 186 (9%) clinically important isolates. Of these, 40 (21%) were isolated only in the Oxoid system and 30 (17%) only in the conventional system. One hundred and sixteen (62%) were isolated from both systems. Volume of blood was not significantly associated with the rate of detection but was significantly associated with the speed of detection. A continuation of the study with a Signal bottle and single conventional bottle confirmed initial results of the increased isolation rate using two systems. The Oxoid single bottle blood culture system was at least comparable with a conventional system in terms of rate of detection of organisms and was superior in terms of speed of detection.     

Effect of altered headspace atmosphere on yield and speed of detection of the Oxoid Signal blood culture system versus the BACTEC radiometric system.

The one-bottle Oxoid Signal blood culture system altered to provide a more aerobic bottle headspace was reassessed in a comparative study versus the two-bottle BACTEC radiometric system in 5,426 blood cultures. The BACTEC system detected more microorganisms (P less than 0.02), particularly anaerobes (P less than 0.05) and fungi (P less than 0.05).     

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 °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.     

Comparison of an agar slide blood culture device with Bactec 6B for the detection of bacteremia

Each of 1,018 blood culture specimens was inoculated into Bactec 6B (Johnston Laboratories, Towson, MD) and a biphasic blood culture system that incorporates internal removable agar dip slides (Hylab). Ninety clinically significant pathogens were recovered: 66 from both systems, 14 from Bactec only, and 10 from Hylab only. The mean incubation times to positive of the two systems did not differ when data were examined for gram-negative bacilli, gram-positive cocci, total isolates, and contaminants (P greater than 0.05). Contamination rates were also comparable: Bactec 5.4%, Hylab 7.3% (P greater than 0.05). The Hylab system may offer a practical alternative to Bactec 6B.     

Comparison of Bactec NR-660 and Signal systems.

Bactec NR-660, a computerised blood culture system using infrared analysis of microbial generated carbon dioxide, was compared with the Signal system, which detects gaseous pressure (due to bacterial metabolism) by a manometer. Four trials were undertaken: an in vitro evaluation of 99 bacteria in simulated blood cultures, and three prospective comparisons of a total of 2588 paired patient samples. Combined results for bacteria in simulated blood cultures showed a highly significant difference (p less than 0.001) between Bactec NR-660 aerobic medium (6A) and any other phial under test. Detection rates for most bacteria by Signal were on average three times slower than the first Bactec phial (mean delay 58.3 hours). Overall, the systems were not comparable.     

Comparison of the Oxoid Signal blood culture system with supplemented peptone broth in a pediatric hospital.

We compared the Oxoid Signal bottle (Oxoid, U.S.A.) with supplemented peptone broth (SPB) tubes (B-D Vacutainer; Becton Dickinson Vacutainer Systems) for performing blood cultures in a pediatric hospital. Blood from 3,066 samples was divided equally between the two systems. Of 131 probable pathogens isolated, 121 were detected in the Signal bottle and 111 were detected in the SPB tubes (P greater than 0.05). Of 167 probable contaminants, 122 grew in the Signal bottle and 109 grew in the SPB tubes (P greater than 0.05). The recovery of staphylococci, both probable pathogens and probable contaminants, was increased in the Signal bottle. The recoveries of other organisms, including streptococci, members of the family Enterobacteriaceae, and yeasts, were similar in the two systems. However, the Signal bottle failed to detect three isolates of Haemophilus influenzae, and the time to availability of isolated colonies of other isolates of H. influenzae was delayed. Overall, the Signal bottle was easy and convenient to use, and its innovative detection system should facilitate the early recognition of positive cultures. If its ability to recover H. influenzae can be improved, the Signal bottle could be a useful alternative to existing systems for use in a pediatric setting.     

Comparison of resin-containing BACTEC Plus Aerobic/F* medium with conventional methods for culture of normally sterile body fluids

The sensitivity of culture in Bactec Plus Aerobic/F* culture vials of body fluids from adult patients at a university hospital was compared with that of conventional culture methods, including enrichment in Schaedler broth. Previous antibiotic therapy was recorded at the time of sampling. Analysis of culture results took account of the clinical significance of isolates and impact on therapy. Of 336 specimens evaluated, 81 (24%) yielded positive cultures, of which 50 cultures (15%) were considered to be clinically significant (yielding 71 isolates) and 31 (9%) were considered contaminated. Of the 71 pathogens, 16 (23%) were isolated in the Bactec system only, whereas 13 (18%) grew in conventional media only; 12 of the latter were strict anaerobes. Among clinically significant positive specimens, 19 (38%) were from patients receiving antibiotic therapy. In 27 cases (8% of all specimens and 54% of significantly positive cultures), the isolation of a pathogen led to modification of therapy. Overall, culture in the Bactec system showed higher sensitivity for the isolation of aerobic micro-organisms than Schaedler broth. Most of the difference was due to a better recovery of Streptococcaceae. Additional pathogens found only in resin-containing Bactec media led to 30% of all culture-influenced modifications of empirical therapy. These data confirm that culture of normally sterile body fluids frequently yields results that are useful for guiding therapy. Although more costly than standard enrichment broth, the resin-containing Bactec Plus Aerobic/F* vial can be advantageous for culture of aerobic pathogens from these specimens, particularly in patients receiving antibiotic therapy.     

Effect of agitation and terminal subcultures on yield and speed of detection of the Oxoid Signal blood culture system versus the BACTEC radiometric system.

In an initial evaluation, we found the Oxoid Signal blood culture system inferior to the BACTEC radiometric system for detection of some microorganisms causing septicemia (M. P. Weinstein, S. Mirrett, and L. B. Reller, J. Clin. Microbiol. 26:962-964, 1988). To determine whether modified processing of the Oxoid Signal blood culture system could improve its yield and speed of detecting positive cultures relative to the BACTEC radiometric system, we agitated all Oxoid bottles during the first 24 to 48 h of incubation and performed aerobic and anaerobic subcultures of all Oxoid bottles negative after 7 days of incubation. These modifications improved the overall performance of the Oxoid system, particularly with regard to the yield of streptococci, members of the family Enterobacteriaceae, and Haemophilus, Neisseria, and Acinetobacter spp. The speed of detecting positive cultures also was improved, especially within the first 24 h of incubation. However, the BACTEC system still detected more positive cultures (P less than 0.005), especially of obligate aerobes such as Pseudomonas aeruginosa (P less than 0.05) and yeasts (P less than 0.005). The BACTEC system also detected positive cultures earlier than the Oxoid system (e.g., at 24 h of incubation, 70.5% of BACTEC positive cultures detected versus 62.1% of Oxoid positive cultures detected). Further modifications of the Oxoid system which might include a revised medium, additional processing modifications, altered headspace atmosphere, or a complementary second broth medium should be considered, since the system is attractive in concept and is easy to use in the clinical laboratory.     

Comparison of BacT/Alert with Signal blood culture system.

The BacT/Alert (Organon Teknika Corp., Durham, N.C.) is an automated blood culture system. It is based on the detection of CO2 by means of a colorimetric sensor internally attached to the bottom of culture bottles. The aerobic and anaerobic media of this system were compared with one bottle of the Signal system (Oxoid Ltd., Hampshire, United Kingdom). At bedside, 20 ml of blood was drawn from each adult patient. The two BacT/Alert bottles were inoculated with 5 ml of blood each; the Signal bottle was inoculated with 10 ml. A total of 5,284 sets (2,483 patients; 2.1 cultures per patient) consisting of three bottles each were evaluated, of which 781 sets (14.8%) revealed microorganisms (n = 892); 642 of these were considered to be pathogenic. Significantly more (P < 0.0001) pathogens were isolated from the two BacT/Alert bottles together (n = 584) than from the single Signal bottle (n = 515). Escherichia coli (P = 0.007), gram-negative bacteria other than members of the family Enterobacteriaceae or Pseudomonas spp. (P = 0.006), and yeasts (P = 0.02) were isolated more often from both or either BacT/Alert bottle. Comparing the systems in terms of 388 different organisms per septic episode, the difference between BacT/Alert and Signal was significant for the total number of septicemia cases (P = 0.003). More contaminants grew in the BacT/Alert system (173 versus 116; P = 0.0001). False-positive indications were more frequent in the BacT/Alert system, 198 (3.7%) aerobic bottles and 57 (1.1%) anaerobic bottles, than in the Signal bottles, 24 (0.5%) bottles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the lysis centrifugation and radiometric blood culture systems for recovery of yeast

The performance of the Isolator (lysis centrifugation) and Bactec (radiometric) detection systems for the recovery of fungi from blood was studied prospectively by comparison of 2,188 paired cultures obtained at two geographically separated teaching hospitals. Eight-three yeast isolates were recovered from 78 (3.6%) cultures that were obtained from 43 patients. Seventy-three (88%) yeast strains were recovered using the Isolator system, and 60 (72%) were recovered in the Bactec system. The average time for recovery of yeast was 2.3 days for the Isolator system and 3.1 days for the Bactec system. Optimal recovery can be accomplished through the use of both systems.     

Comparison between Bactec Nr. 660 and a conventional 12-tube blood culture system

The detection power of the automated blood culture system Bactec NR 660, based on infrared detection of carbon dioxide in an agitated aerobic medium and a non-agitated anaerobic medium, was compared with that of our conventional 12-tube blood culture system. Of 1685 paired blood cultures, 258 (15.3%) were positive in one or both systems. Clinically relevant isolates were found in 11.5%. The dominating species were Escherichia coli(41%), followed by Staphylococcus aureus(14%) and Klebsiella spp.(8%). The Bactec system detected 178 (10.6%) and the 12-tube system 157 (9.3%) clinically relevant microorganisms after seven days' incubation. Significantly more clinically relevant isolates were detected by the Bactec system alone as compared with the conventional system alone (40 versus 19, p less than 0.01). The detection time was significantly shorter in the Bactec system for all isolates and for E. coli and S. aureus separately (p less than 0.01). 1.8% of the isolates in the Bactec system and 2.1% in the 12-tube system were considered clinically non-relevant contaminants.     

Comparative evaluation of nonradiometric BACTEC and improved oxoid signal blood culture systems in a clinical laboratory.

The BACTEC NR660 blood culture system, which uses infrared spectroscopy to detect carbon dioxide generated by bacterial growth, was compared with the new medium formulation of the Oxoid Signal system. Two trials were conducted: a comparative study of 88 organisms in simulated blood cultures and a clinical trial of 3,321 paired patient blood culture samples. Both trials showed that overall the BACTEC system performed better in the recovery of organisms. The Oxoid system was unable to detect by signal the growth of the majority of yeasts, nonfermentative gram-negative bacilli, Neisseria meningitidis, Nocardia spp., and Corynebacterium jeikeium. There were no significant differences in the yield of Staphylococcus spp., members of the family Enterobacteriaceae, Streptococcus spp., or anaerobic organisms. BACTEC detected growth more quickly than did the Oxoid system; 61% of the isolates were detected by BACTEC at 24 h, while 49% of the isolates were detected by Oxoid. The Oxoid system had a high proportion (58.5%) of false-positives, compared with 7.7% for the BACTEC system. Despite the new medium formulation of the Oxoid system, its performance is still not equivalent to that of the BACTEC system.