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.