Controlled clinical laboratory comparison of two supplemented aerobic and anaerobic media used in automated blood culture systems to detect bloodstream infections.
A 20-ml blood sample was collected from adult patients with suspected bloodstream infections and distributed equally into the four volume-controlled bottles of a blood culture set consisting of aerobic and anaerobic BACTEC Plus/F bottles and aerobic and anaerobic BacT/Alert FAN bottles. All bottles were incubated in their respective instruments for a standard 5-day protocol or until the instruments signalled positivity. Samples in all bottles with negative results by these instruments were terminally subcultured. A total of 8,390 blood culture sets were obtained during the study period, of which 4,402 (52.5%) met the study criteria. Of these, 946 (21.5%) were positive either by instrument signal or by additional terminal subculture of all negative bottles and yielded growth of microorganisms. Five hundred eighty-nine (13.4%) blood culture sets were considered to have recovered 663 clinically significant organisms. When both the BACTEC and the BacT/Alert systems were used, 465 positive sets were detected; BACTEC alone detected 52 positive sets and BacT/Alert alone detected 72 (P = 0.09). No differences were found between the two systems in microbial recovery rate from blood cultures obtained from patients on antibiotic therapy. Significantly more members of the family Enterobacteriaceae (P < 0.01) were detected from patients without antimicrobial therapy by BacT/Alert than by BACTEC. The false-negative rates were 0.20% for BACTEC and 0.32% for BacT/Alert. A significantly higher false-positive rate was found for BACTEC (P < 0.0001). Both systems were comparable for the time to detection of microorganisms. However, gram-positive bacteria were detected faster by BACTEC and Enterobacteriaceae were detected faster on average by BacT/Alert. We concluded that both systems are comparable in their abilities to recover aerobic and anaerobic organisms from blood cultures and a terminal subculture might not be necessary for either of the two systems. The increased positivity rate when using an anaerobic bottle in a two-bottle blood culture set is due to the additional blood volume rather than to the use of an anaerobic medium.
Ziegler
R
R
Institut für Klinikhygiene, Medizinische Mikrobiologie und Klinische Infektiologie, Klinikum Nürnberg, Germany.
Johnscher
I
I
Martus
P
P
Lenhardt
D
D
Just
H M
HM
D000328:Adult; D000332:Aerobiosis; D000693:Anaerobiosis; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D016470:Bacteremia / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology; D001421:Bacteria, Anaerobic / Q000302:isolation & purification; D001769:Blood / Q000382:microbiology*; D003470:Culture Media; D004755:Enterobacteriaceae / Q000302:isolation & purification; D005188:False Negative Reactions; D005189:False Positive Reactions; D016469:Fungemia / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology; D006094:Gram-Positive Bacteria / Q000302:isolation & purification; D006801:Humans; D011897:Random Allocation
D000900:Anti-Bacterial Agents; D003470:Culture Media