Routine subcultures shown to be unnecessary in radiometric detection of bacteremia using three media

A study to determine the necessity of routine blind subcultures when using the radiometric BACTEC-460 instrument for detection of bacteremia was conducted. In the first phase, blind subcultures were performed on day 10 of incubation; in the second phase, blind subcultures were performed on day 4; in the final phase the subculture was performed on day one. During the study, 6,208 blood cultures from 2,455 patients were inoculated into three different culture media. There were 454 microbial isolates recovered, including 269 presumed pathogenic isolates. The single significant discrepancy between blind subculture and radiometric detection was a case of Staphylococcus epidermidis septicemia in which the organism was detected 48 hours earlier by blind subculture. There were no cultures in which significant bacterial isolates were detected by blind subcultures but not radiometrically. Thus, under the conditions of this study, routine blind subcultures are not necessary when using the BACTEC radiometric system for detection of bacteremia.