SIGNAL blood culture system for detection of bacteremia in neonates

In the SIGNAL (Oxoid Ltd., Basingstoke, United Kingdom) blood culture system, gas produced by bacterial metabolism displaces medium from the culture bottle into an upper reservoir via a hollow needle. Displacement of media may provide a visual indication of the presence of both aerobic and anaerobic organisms in a single medium. The single-bottle SIGNAL system was compared with paired BACTEC 16B and 7D (Johnston Laboratories, Inc., Towson, Md.) radiometric system bottles by using bacterial inocula and conditions which simulated those found in neonatal and pediatric populations. The single SIGNAL bottle was a good as the combined BACTEC media for Escherichia coli and Staphylococcus aureus, but was slower for Candida spp., Haemophilus influenzae, Pseudomonas aeruginosa, Staphylococcus epidermidis, group B streptococci, alpha-streptococci, and pneumococci. The SIGNAL system failed to detect four of five isolates of Neisseria meningitidis and four of eight anaerobic organisms. The SIGNAL system is not suitable for neonatal blood cultures at its present state of development.