Evaluation of BACTEC 9240 blood culture system by using high-volume aerobic resin media.

The BACTEC 9240 blood culture system (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.) is one of three automated, continuous-monitoring systems that is widely used in clinical laboratories. The BACTEC 9240 was compared with the BACTEC NR 660 for the detection of organisms and bacteremic episodes; time to detection of positive cultures; number of false-positive and false-negative cultures; and time needed to load, process, and perform quality control functions by using high-volume aerobic media. Blood specimens (5,282) were inoculated in equal volumes (5 to 10 ml per bottle) into BACTEC Plus Aerobic/F (9240 system) and BACTEC Plus NR26 (660 system) bottles. Clinically significant isolates were detected in 6.6% of cultures, representing 348 microorganisms and 216 bacteremic episodes. Two hundred forty-eight microorganisms were detected by both systems, 48 by the 9240 only and 52 by the 660 only (P = not significant). Of the bacteremic episodes, 158 were detected by both systems, 27 by the 9240 only and 31 by the 660 only (P = not significant). Analysis of data by month revealed equivalent recovery rates for both systems, with the exception of a 30-day period at one study site during which the 660 system detected significantly more microorganisms. Following a proprietary hardware design retrofit of the 9240 instrument, detection rates were again equivalent for the remaining three months at this study site. Positive cultures detected by both systems were detected an average of 4.3 h faster by the 9240 system (21 versus 25.3 h). The numbers of false-positive cultures for the 9240 and 660 systems were 40 (1.0%) and 9 ( < 1.0%), respectively. The numbers of false-negative cultures were five for the 9240 system and three for the 660 system. The 9240 system required 23 s less technologist time per bottle to operate during the 5-day protocol. In conclusion, the BACTEC 9240 used with high-volume Aerobic/F medium is equivalent to the BACTEC 660 used with high volume NR26 medium for the detection of microorganisms and bacteremic episodes. In addition, the 9240 system detects positive cultures more rapidly than the 660 system but requires further evaluation to ensure reliability of instrument components.

Multicenter clinical evaluation of a continuous monitoring blood culture system using fluorescent-sensor technology (BACTEC 9240).

The BACTEC 9240 (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.) is a new continuous-monitoring blood culture system that uses internal, fluorescent-CO2 sensors. In a multicenter clinical trial, organism yield and times to detection with the prototype BACTEC 9240 system were compared with those of the BACTEC NR 660 system. Equal volumes of blood were inoculated into the bottles included in the study blood culture sets (aerobic and anaerobic 9240 and NR6A and NR7A bottles). A total of 9,391 aerobic and 8,951 anaerobic bottle pairs were inoculated with 9,801 blood specimens. A total of 587 clinically significant positive blood cultures and 415 cases of sepsis were studied. The standard 9240 aerobic bottle detected significantly more Staphylococcus aureus (P < 0.05), coagulase-negative staphylococci (P < 0.01), and total microorganisms (P < 0.001) than the NR6A bottle. The standard 9240 anaerobic bottle detected significantly more coagulase-negative staphylococci (P < 0.001), members of the family Enterobacteriaceae (P < 0.01), and total microorganisms (P < 0.001) than the NR7A bottle. A total of 420 positive cultures were detected in both systems; for 284, the time to detection was equivalent with both systems (within 12 h); for 123, the 9240 system was faster; and for 13, the NR 660 system was faster (P < 0.001). The average times to detection for the 9240 and the NR 660 systems were 20.2 and 27.5 h, respectively. Ninety-nine cultures were positive only in the 9240 system, and 68 cultures were positive only in the NR 660 system (P < 0.02). The 9240 system also detected significantly more episodes of bacteremia (P < 0.001). The false-positive rates for the 9240 and NR 660 systems were 2.2 and 2.3%, respectively. The false-negative rates for the two systems after 5 days of incubation did not differ significantly. The contamination rates for the 9240 and NR 660 systems were 1.9 and 1.5%, respectively (P < 0.05). In conclusion, the prototype 9240 system detected more clinically significant positive blood cultures and did so sooner than the NR 660 system, with the additional advantages of full automation, continuous monitoring, and noninvasive sampling.

Comparison of TestPack Plus Strep A with selective and nonselective culture media for detection of group-A streptococci.

The TestPack Plus Strep A (TPPSA), an immunoassay method, was compared with conventional culture methods including nonselective trypticase soy agar with 5% sheep blood and selective SXT blood agar for detection of group-A streptococci (GAS). A total of 452 throat swabs was evaluated, of which 261 (57.7%) and 191 (42.3%) were compared with culture using nonselective and selective media, respectively. Of 261 specimens evaluated on nonselective media, 71 (27.1%) were culture positive for GAS. TPPSA demonstrated a sensitivity of 91.6% and a specificity of 94.2% with positive and negative predictive values of 85.5% and 96.8%, respectively. Of 191 specimens evaluated on selective media, 44 (23.0%) were culture positive for GAS. TPPSA demonstrated a sensitivity of 93.2% and a specificity of 98.0% with positive and negative predictive values of 93.2% and 98.0%, respectively. The performance of TPPSA when compared with nonselective and selective media demonstrated a similar sensitivity, but a higher specificity was seen when compared to selective media. Overall, TPPSA was extremely easy to perform, had built-in procedural controls, required minimal technologist time, and was easy to interpret. With an accuracy of 93.5% when compared with nonselective media and 96.9% when compared with selective media, TPPSA could be recommended as a reliable method for detection of GAS.

A comparison of oxoid signal with nonradiometric BACTEC NR-660 for detection of bacteremia.

The Oxoid Signal (Oxoid U.S.A. Inc., Columbia, Maryland) system was compared with the nonradiometric BACTEC NR-660 (Johnston Laboratories, Towson, Maryland) system for detection of bacteria in 2714 blood cultures. The volume of blood collected into 20 ml blood-collection tubes containing sodium polyanetholsulfonate (SPS) (Becton Dickinson, Vacutainer Systems, Rutherford, New Jersey) ranged from 10 to 20 ml with an average of 15 ml. Subsequently, equal volumes of blood were inoculated into each system. A total of 250 organisms was isolated (9.6%), of which 149 (5.5%) were considered significant while 111 isolates from 98 cultures (3.6%) were contaminants. Of the significant isolates 32.9% were aerobic Gram-negative rods, 53.0% aerobic Gram-positive cocci, 5.4% anaerobes, 7.4% yeasts, and two isolates of Neisseria meningitidis. Ninety-five isolates were recovered in both systems, 29 by Bactec only and 25 by Signal only. Of the isolates recovered there were no significant differences in detection between the two systems with the exception of anaerobes (p less than 0.005). The median detection times for many of the most commonly isolated organisms--Enterobacteriaceae, streptococci, and Staphylococcus aureus--were very similar in both systems, ranging from 14 to 21 hours. With the remaining organisms recovered, the median times in hours for BAC-TEC and Signal, respectively, were 31 and 47 for Staphylococcus epidermidis, 48 and 60 for Bacteroides, 39 and 168 for yeast, and 16.5 and 168 for N. meningitidis. Oxoid Signal compares favorably with the BACTEC system. Its main advantages are: (1) it requires no instrumentation; (2) it is characterized by ease of detection; and (3) it uses a single-bottle system.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Comparison of TestPack Strep A test kit with culture technique for detection of group A streptococci.

Results obtained with Abbott Laboratories TestPack Strep A (TPSA), a 7-min enzyme immunoassay method, were compared with culture results to measure the ability of this assay to detect group A streptococci directly from 365 throat swabs. Our study demonstrated a sensitivity of 90.0% and a specificity of 97.4% for TPSA compared with cultures incubated for 48 h. The positive and negative predictive values of this assay versus the culture method were 92.8 and 96.3%, respectively. If specimens that provided fewer than 10 colonies per plate of group A streptococci are eliminated from the data, the sensitivity is increased to 95.6%. Additionally, 10 group A and 40 non-group A streptococcal isolates were tested directly with TPSA for the ability to distinguish group A from non-group A streptococci. All 50 isolates were correctly identified (100% accuracy). TPSA is a rapid, accurate, and easy-to-interpret method for detection and confirmation of group A streptococcal antigen directly from throat swabs and pure culture isolates.