[Automatic detection of bacterial and fungal infections in blood]

Sepsis is one of the main causes of mortality and morbidity in hospitals. Early detection of pathogens using nucleic acid-based techniques speeds diagnosis of bacteremia and/or fungemia, aids the rapid application of appropriate antibiotics, reduces the use of unnecessary antibiotics, and lowers mortality. Two commercially available techniques that help to identify different sepsisproducing bacteria and fungi in a shorter time period are: LightCycler SeptiFast Test Mgrade (Roche Diagnostic SL) and GenoType Blood Culture (Hain Lifescience). We present the results of an initial in-house study using the LightCycler SeptiFast Test Mgrade. The study was carried out in 50 samples from 28 patients (1-3 samples per patient) with septic syndrome admitted to the intensive care unit by comparing the new technique with conventional blood culture. The concordance between the results of blood culture and SeptiFast was good, 79%, in the first trial and 89% in the second, after correcting for technical defects. We initially observed substantial inhibition of internal controls in Gram-negative bacilli, due to the presence of heparin in the blood used, and excess DNA because of the high number of leucocytes. To minimize these inhibitions, the second study used 24 samples at half the original volume (extracted DNA at 1/4 concentration). With these modifications, inhibitions were substantially reduced. SeptiFast is more effective than blood culture in discriminating between contamination by coagulase-negative staphylococci and species of streptococci.