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

Novel automated microbial screening of platelet concentrates

The recovery of bacteria and the speed of detection of microbial growth in platelet concentrates (PC) were studied, comparing a novel automated blood culture system (BacT/Alert) with two traditional methods. Full-scale experiments were performed with a total of 33 units of PC (average content 320 x 10(9) platelets per unit) obtained from pooled buffy coats. Six strains known as possible PC contaminants were tested: S. epidermidis, S. aureus, P. aeruginosa, B. cereus, E. aerogenes, and S. sanguis. Using an inoculum of 50-98 bacteria/ml, bacterial contamination was detected in all of 11 PCs on 132 sampling occasions. With a small inoculum (0.3-9 bacteria/ml), the bacterial contamination was detected in all PCs in which abundant growth appeared, but failed to be detected in some instances where the bacterial content was very small. All of 11 uninoculated PC controls were negative. With the automated method the time for detection of a culture-positive PC was 6-16 h, clearly shorter than with the two manual-visual systems. The new system provides a rapid, reliable, and labour-saving method for screening of bacterial contamination in PCs. This would increase safety particularly if the present 5-day shelf life were extended.

Comparison of detection speed and yield in agitated and non-agitated aerobic blood culture bottles

The influence of agitation on detection speed and yield was evaluated in 7,033 paired, identical aerobic blood culture bottles (Media Department, Statens Seruminstitut, Copenhagen, Denmark). One bottle was agitated and the other was incubated stationary. Of a total of 943 organisms isolated in aerobic blood culture bottles, 74% were clinically significant. No difference in the total yield of significant organisms was observed between agitated and non-agitated bottles. In the evaluation of detection speed, only cultures where organisms were isolated from both bottles, but at different times, were included, to ensure that no other factors influenced the result. Staphylococci, Pseudomonas spp., and Candida spp. were detected significantly faster in agitated bottles, on average 0.5-1 day earlier (p < 0.05), and in the majority of the cases within the first incubation day. These species are frequently found and are important causes of severe generalized infections, especially in immunocompromised patients, where early detection is of great importance. The detection principle in agitated bottles in our system, darkening of blood, proved to be an easy, reliable, and fast method to detect positive aerobic blood cultures, which could probably lead to increased automation.

Darkening of haemoglobin in simulated, continuously agitated aerobic blood cultures: an early indicator of bacterial growth

The change of purple oxyhaemoglobin to the darker reduced haemoglobin and methaemoglobin was used as an initial visual growth indicator in continuously agitated, aerobic Colorbact bottles after inoculation with a broad assortment of aerobic and facultatively anaerobic bacteria previously isolated from blood cultures. Growth of all the faster growing strains could be detected by darkening of the blood cultures within a 24 h period of agitation, after they had stood unshaken for eight h. The darkening was accompanied by consumption of O2 and acidification of the fluid media. The slower growing bacteria were detected by turbidity. This growth detection method is easy, quick, inexpensive and reliable, and is especially promising for application in clinical microbiological departments which daily receive blood cultures from peripheral hospitals.

Colorbact, a visually read blood culture system using darkening of haemoglobin in aerobic blood cultures as an early growth indicator, compared with Bactec 6A and 7A

Colorbact-A (aerobic), a blood culture system using darkening due to oxygen reduction and acidification of haemoglobin as an initial growth indicator during the first day of incubation of continuously agitated, aerobic blood cultures, was compared with the 24 h agitated aerobic Bactec 6A in 1767 consecutive paired cultures. Both systems were examined simultaneously twice daily during the first two days and once daily the next five days of incubation. In addition, during the agitation period Colorbact-A was observed for darkening four to five times during day duty between 8 a.m. and 4 p.m. The final seven days detection rate found by Colorbact-A using observation for darkening during initial agitation was similar to the rate found by Bactec 6A for both clinically significant strains and "contaminants", but Colorbact-A was significantly faster (p less than 0.001) in finding clinically significant strains. Colorbact-AN (anaerobic) was more rapid (p less than 0.01) and yielded more positive cultures than the anaerobic Bactec 7A. The Colorbact system was flexible, inexpensive, reliable and especially promising for laboratories which receive blood cultures from other hospitals once daily, as many positive cultures can be found immediately on arrival undisturbed by agitation during transport.

Should aerobic blood cultures be shaken intermittently or continuously?

Stationary incubation of aerobic blood cultures was compared with intermittent shaking in aerobic Vacutainer 2630 bottles with agar slants during the first 24 h, and was simultaneously compared with the continuously shaken aerobic Bactec 6A bottles as a reference system. Intermittent shaking did not significantly increase or decrease the seven days yield of the Vacutainer bottles as compared with the continuously agitated Bactec 6A bottles. When one of 604 paired Vacutainer bottles was agitated for eight h and the other incubated stationary, the speed of growth detection was significantly greater in the agitated bottle (p less than 0.001), but significantly less than with continuously agitated Bactec 6A bottles (p less than 0.001). Agitation for 14 h showed the same pattern of detection speed. These results suggest that it is desirable initially to agitate aerobic blood cultures either intermittently or continuously.