[Blood culture update]

Blood culture is one of the most important bacteriological examinations with important clinical and therapeutic consequences. Blood cultures should be ordered in all patients with signs suggesting septicemia, endocarditis or severe infection (pneumococcal pneumonia, bacterial meningitis with bloodstream dissemination). Blood culture methods have evolved considerably over the last twenty years. After using manual methods for many years, read by non-standardized visual methods, the development of media with defined compositions and supplemented to allow growth of bacteria difficult to culture has been associated with the development of automatic blood culture devices.

These devices have undergone rapid improvement. Semi-automatic devices (Bactec NR-660) were rapidly followed by completely automatic techniques, including four devices currently available: since 1989 Bio-Argos (Rio-Rad) and Bact/Alert (Organon-Teknika) and in 1993, Bactec 9240 (Becton-Dickinson) and Vital (BioMérieux). All these devices allow automatic detection of CO2 produced during bacterial growth. Automatic reading systems provide continuous output avoiding the need for invasive methods and thus the risk of contamination in addition to saving time. Potential application to achieve quantitative blood cultures for intensive care units is in the development stage.

The reliability of these devices is well recognized and their contribution to severe bacterial infection is undeniable. There are certain limitations however related to material cost and the non-identification of the pathogen involved. Molecular biology techniques open new perspectives in this field. The evolution of techniques, definitions, and pathogenic approach to septicemia must be revisited as new infectious situations have been identified at the same time as new investigation tools resulting from considerable technological progress. New methods of blood culture have largely contributed to this progress.