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.     

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.     

Evaluation of a blood culture medium BHI-S-Lysis for BCB Release System Roche.

The new blood culture medium BHI-S Lysis for the BCB Release System (F. Hoffmann-La Roche AG., Basel, Switzerland), which lyses blood cells, was compared with the Hémoline performance Duo (BioMérieux, Marcy l'Etoile, France) including a diphasic medium and a modified Wilkins Chalgren broth. A total of 1998 sets were each inoculated with 7 ml of blood. In the laboratory, agar-coated paddles were attached to the BHI-S-Lysis. Overall, there was a statistically significant difference between the BHI-S-Lysis and the diphasic medium, or Wilkins Chalgren broth, in the recovery of clinically important microorganisms. The yield of pathogens with the BHI-S-Lysis, diphasic medium and Wilkins Chalgren broth was 115, 68 and 58, respectively. Staphylococci were detected by the BHI-S-Lysis significantly more frequently. Out of 50 bacteraemias, 12 were diagnosed with the BHI-S-Lysis only, three with the diphasic medium only, and three with the Wilkins Chalgren broth only. Contaminant isolates occurred with significantly greater frequency in the BHI-S-Lysis than in the two BioMérieux systems, in particular with coagulase-negative staphylococci. No speed advantage was present for all groups of micro-organisms and blood culture media. This good performance of the BHI-S-Lysis medium in detecting a larger number of pathogens should be confirmed by further evaluations.     

The clinical comparison of Oxoid Signal with Bactec blood culture systems for the detection of streptococcal and anaerobic bacteraemias.

Blood cultures were taken from 47 patients 1-2 min after dental extraction. These samples were tested by the radiometric Bactec 460 and Oxoid Signal systems for the detection of streptococcal and anaerobic bacteraemias. Streptococci were isolated from 19 (40%) patients and anaerobes from 15 (32%). In this study the Oxoid Signal system was significantly better for isolating oral anaerobes than the Bactec system; five isolates were obtained with the Bactec system and 14 with the Signal system. There was no significant difference in the isolation of streptococci between these two systems (Bactec 14, Oxoid Signal 10). The contamination rate was 4.1% for Bactec and 7.5% for the Oxoid Signal system.     

Clinical comparison of the Roche Septi-Chek and Dupont Isolator blood culture systems

A study was conducted to compare the recovery of clinical isolates by the DuPont Isolator and Roche Septi-Chek blood culture systems. A total of 5,262 blood culture specimens were processed by the two systems. Of these, 358 cultures contained significant isolates: 219 were positive in both systems, 68 were recovered only by Isolator, 71 were recovered by Septi-Chek only (not statistically significant). Of the isolates recovered in both systems, 159 were positive the same day, 55 were recovered first by Isolator, and 5 were recovered first by Septi-Chek. In cases where Isolator recovered organisms first, the average difference in time was one to two days. Regarding particular groups of organisms, there was no difference between the systems in recovery of Enterobacteriaceae, anaerobes, yeast, and gram-positive bacteria, except for Streptococcus pneumoniae. Septi-Chek recovered S. pneumoniae significantly more often. These results suggest that these two systems are essentially comparable, except with S. pneumoniae, although the Isolator frequently provided results more rapidly.     

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.     

Controlled evaluation of BACTEC PLUS 27 and Roche Septi-Chek anaerobic blood culture bottles.

Becton Dickinson Diagnostic Instrument Systems (Sparks, Md.) recently introduced BACTEC high-volume aerobic and anaerobic bottles that accept up to 10 ml of blood for use on their nonradiometric blood culture instruments. Both bottles contain 25 ml of tryptic soy broth, 0.05% sodium polyanetholesulfonate, and mixed resins. We compared the anaerobic bottle, designated BACTEC PLUS 27 (BP27), with the Roche Septi-Chek (RSC) Columbia broth anaerobic bottle in a collaborative evaluation at three university hospitals. A total of 5,152 adequately filled blood cultures were obtained from adult patients with suspected bacteremia or fungemia. Staphylococcus aureus was recovered significantly more often (P less than 0.03) from BP27 bottles alone; there were no other significant differences in yield. When microorganisms were recovered from both anaerobic bottles, growth was detected earlier in BP27 than it was in RSC (P less than 0.001), especially for S. aureus (P less than 0.001) and Staphylococcus epidermidis (P less than 0.02). We conclude that the yield from BP27 bottles is equivalent to or better (S. aureus) than that from RSC anaerobic bottles with Columbia broth and that speed of detection is superior with BP27 bottles.     

Controlled evaluation of BACTEC Plus 26 and Roche Septi-Chek aerobic blood culture bottles.

Blood culture bottles that accept up to 10 ml of blood have recently been introduced for the BACTEC nonradiometric blood culture system. The new formulation, designated BACTEC Plus, contains 25 ml of tryptic soy broth, 0.05% sodium polyanetholesulfonate, and mixed resins. In a collaborative study conducted at three university hospitals, we evaluated the BACTEC Plus 26 (BP26) aerobic bottle and the Roche Septi-Chek aerobic bottle with its agar slide paddle in 5,293 paired blood cultures. Significantly more microorganisms (P less than 0.001), especially Staphylococcus aureus (P less than 0.001), Staphylococcus epidermidis (P less than 0.01), enterococci (P less than 0.005), and members of the family Enterobacteriaceae (P less than 0.005), were detected by the BP26 bottle. When both bottles detected growth, BP26 did so earlier (P less than 0.001). In particular, S. epidermidis (P less than 0.001), streptococci (P less than 0.005), enterococci (P less than 0.05), and members of the family Enterobacteriaceae (P less than 0.001) were detected earlier by the BP26 bottle. We conclude that the BP26 bottle provides a yield and speed of detection of microorganisms superior to those of the Roche Septi-Chek aerobic blood culture bottle.     

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.     

Comparison of Roche blood culture bottle with an in-house conventional blood culture system.

A comparison was made of the in-use performance of an in-house broth blood culture in a general hospital during 8 mths in 1988 with that of a commercial biphasic culture (BCB system, Roche Products Pty Ltd, Sydney) for the corresponding period in 1989. The clinical services and the number of blood samples tested were comparable. The yields of organisms after 48 hrs incubation were similar in both systems. Staphylococcus aureus showed up 3 times as often after 24 hrs incubation in the conventional system as in the BCB system. Agitation of the BCB facilitated macroscopic detection of growth in the initial 24 hrs incubation.     

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).     

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.     

Comparative evaluation of the Roche Cobas IDA and Enterotube II systems for identifying members of the family Enterobacteriaceae.

Two Hoffmann-La Roche products were evaluated in parallel for their ability to identify 321 strains of the family Enterobacteriaceae. The first product was the well-established Enterotube II, which correctly identified 90% of the isolates after 24 h of incubation. The second was the ID-E rotor, originally designed for use in the Cobas Bact but here used in the new Cobas IDA system. The Cobas IDA, used with the full data base held in a microcomputer supplied with the product, identified 87% of strains after 4 h of incubation.     

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.     

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.     

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.