Blood Culture Methodologies and Reporting
Routine adult and pediatric blood cultures are processed using the BD Bactec continuously monitored blood culture system. From the time the sample is placed in the Bactec module, the culture is read every 10 minutes using a colorimetric sensor to monitor for the production of CO2, indicative of microbial growth.
The Bactec media and system will detect most fastidious organisms, including HACEK group organisms, using our standard incubation periods. However, if Brucella or Francisella are included in the differential, contact the Microbiology Lab (4-1805), as these organisms may require additional incubation time. (No additional media are required for these organisms.)
Negative results are updated automatically to the Laboratory Information System and to the Clinical Workstations hourly; after five days incubation and continuous monitoring, cultures which have not been detected as positive are finalized as "No Growth After 5 Days".
When the instrument indicates that a culture has become positive, a Gram's stain of the positive bottle is performed and subcultures are made to appropriate media. Initial, first-time positive blood cultures are immediately called to the ordering physician. Subsequent, repeat positives are not called unless the Gram's stain indicates a different organism(s).
Positive blood cultures with Gram stain consistent with Gram-positive cocci in pairs and chains, will automatically have a rapid molecular identification test performed.
Blood Cultures for Acid Fast Bacilli (Mycobacterium sp.) are similarly monitored by the Bactec system. Negative results are updated automatically to the LIS and Clinical Workstations weekly; cultures are incubated for six weeks before being given a final result of Negative.
Blood Culture Mould is intended for the recovery of dimorphic (endemic) fungi, Fusarium sp., Trichosporon sp., and the lipid-dependent yeast, Malassezia furfur. These are set up using one routine aerobic Bactec bottle, one Bactec Myco/F Lytic bottle and the Wampole IsolatorTM system. The Isolator tube contains lytic agents and is inoculated directly onto selective &/or enriched media specific for the moulds suspected; therefore, it is essential that the laboratory is informed of the suspect organism at the time of ordering. Media are incubated for three weeks before being given a final result of Negative. Call the Bacteriology Laboratory at 984-974-1805 for more information.
Blood Culture Guidelines
- A Total of 4 Blood Cultures are allowed during the first 48 hours of suspected sepsis
- Two Additional Blood Cultures are permitted every 48 hours following the initial 4 blood cultures, if clinical condition warrants
- "Test of Cure" Cultures may be drawn 48 hours after clinically significant, positive blood cultures are obtained
- Exceptions to these Guidelines require consultation with Microbiology (984) 974-1805