Clinical comparison of a new automated infrared blood culture system with the BACTEC 460 system

Abstract

A new blood culture instrument, the BACTEC (Johnston Laboratories, Inc., Towson, Md.) NR-660, which utilizes infrared detection of carbon dioxide from microbial metabolism, was compared with the radiometric BACTEC 460 system. There were 1,554 isolates from 18,785 paired aerobic blood cultures. Of these isolates, 1,303 were isolated from the radiometric 6B medium, and 1,259 were isolated from the NR6A medium (P = 0.06). Analysis of the data indicated no significant differences in recovery when any individual species was considered. When organisms were considered as groups, there were no significant detection differences for gram-negative bacilli, yeasts, or anaerobes. For gram-positive cocci in aerobic medium, the BACTEC 460 detected 84.3% of the total isolates, and the BACTEC NR-660 detected 79.7% (P = 0.04). There were 891 isolates from 13,983 paired anaerobic blood cultures. Of these isolates, 725 were recovered from the radiometric 7D BACTEC medium, and 723 were recovered from the NR7A BACTEC medium (P > 0.9). In the anaerobic media there was no significant difference in detection of any organism group, including the gram-positive cocci. When the results of the aerobic and anaerobic media were combined, there was equivalence between the two systems for the detection of gram-positive cocci (P > 0.2) and other organism groups. When the ability to detect septic episodes was compared, there was no significant difference for any organism group (P = 0.12). For aerobic media, the mean times for detection were 30.5 and 29.5 h for the BACTEC 460 and NR-660, respectively. For anaerobic media, the mean times for detection were 39.8 and 41.6 h for the BACTEC 460 and NR-660, respectively. Compared with the BACTEC 460, the BACTEC NR-660 system had a greater ease of operation, faster test cycle, computerized data base, and equally rapid detection of positive cultures.

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

“…Comparing these two studies from our laboratory we found a similar detection power of Bactec NR 460@ and 660@ in accordance with Jungkind et al (14).…”

Determination of growth value thresholds for BACTEC PLUS aerobic blood culture vials

“…In addition, threshold analysis can determine how efficiently laboratory personnel resources are used to identify cases of bacteremia, a subject of great importance in today's laboratory. Automated instruments like the BACTEC NR660 usually include a management system for data to flag positive vials and to store GV readings for the entire test cycle of a vial, quality control information, and tray testing order (5). Data from our evaluation suggest that including software to periodically VOL.…”

“…bacteremia detection device uses an infrared spectrometer to measure the concentration of carbon dioxide in blood culture vials. When the carbon dioxide concentration increases, the device flags the vial as positive for the growth of microorganisms in the blood sample (5). This involves calculating a growth value (GV) index from a comparison of the current carbon dioxide concentration with a nominal baseline level.…”

“…This involves calculating a growth value (GV) index from a comparison of the current carbon dioxide concentration with a nominal baseline level. The instrument's recording system permits the user to adjust the threshold GV defining a tested vial as positive as well as to define a threshold value for the change in GV from the previous reading (delta reading [DR]) that also will flag a vial as positive for microbial growth (5).…”

Update on detection of bacteremia and fungemia.

“…With 7D medium, the radiometric BACTEC system detected anaerobes at a rate similar to that with conventional media (173). The newer nonradiometric 7D medium performs similarly to radiometric 7D medium, as does the resin-containing BACTEC 27 medium (76,103,206). Too few anaerobic isolates have been recovered during clinical evaluations of CMBCS to adequately assess the capability of these instruments to detect anaerobes.…”