Rapid detection of micro-organisms from blood is one of the most critical functions of a diagnostic microbiology laboratory. Automated blood-culture systems reduce the time needed to detect positive cultures, and reduce specimen handling. The false-positive rate of such systems is 1–10 %. In this study, the presence of pathogens in ‘false-positive’ bottles obtained from BACTEC 9050 (Becton Dickinson) and BacT/Alert (Biomérieux) systems was investigated by eubacterial and fungal PCR. A total of 169 subculture-negative aerobic blood-culture bottles (104 BacT/Alert and 65 BACTEC) were evaluated. Both fungal and eubacterial PCRs were negative for all BACTEC bottles. Fungal PCR was also negative for the BacT/Alert system, but 10 bottles (9·6 %) gave positive results by eubacterial PCR. Sequence analysis of the positive PCR amplicons indicated the presence of the following bacteria (number of isolates in parentheses): Pasteurella multocida (1), Staphylococcus epidermidis (2), Staphylococcus hominis (1), Micrococcus sp. (1), Streptococcus pneumoniae (1), Corynebacterium spp. (2), Brachibacterium sp. (1) and Arthrobacter/Rothia sp. (1). Antibiotic usage by the patients may be responsible for the inability of the laboratory to grow these bacteria on subcultures. For patients with more than one false-positive bottle, molecular methods can be used to evaluate the microbial DNA in these bottles. False positives from the BACTEC system may be due to elevated patient leukocyte counts or the high sensitivity of the system to background increases in CO2 concentration.
CockerillF. R.III,
ReedG. S.,
HughesJ. G. & 7 other authors; 1997; Clinical comparison of BACTEC 9240 Plus Aerobic/F Resin Bottles and the Isolator Aerobic Culture System for detection of bloodstream infections. J Clin Microbiol 35:1469–1472
DurmazG.,
UsT.,
AydinliA.,
KiremitciA.,
KirazN.,
AkgünY.2003; Optimum detection times for bacteria and yeast species with the BACTEC 9120 aerobic blood culture system: evaluation for a 5-year period in a Turkish university hospital. J Clin Microbiol 41:819–821[CrossRef]
FredricksD. N.,
RelmanD. A.1998; Improved amplification of microbial DNA from blood cultures by removal of the PCR inhibitor sodium polyanetholsulfonate. J Clin Microbiol 36:2810–2816
MillarB. C.,
JiruX.,
MooreJ. E.,
EarleJ. A. P.2000; A simple and sensitive method to extract bacterial, yeast and fungal DNA from blood culture material. J Microbiol Methods 42:139–147[CrossRef]
NolteF. S.,
WilliamsJ. M.,
JerrisR. C.,
MorelloJ. A.,
LeitchC. D.,
MatushekS.,
SchwabeL. D.,
DoriganF.,
KockaF. E.1993; Multicenter clinical evaluation of continuous monitoring blood culture system using fluorescent-sensor technology. (BACTEC 9240) J Clin Microbiol 31:552–557
QianQ.,
TangY.-W.,
KolbertC. P. & 7 other authors; 2001; Direct identification of bacteria from positive blood cultures by amplification and sequencing of the 16SrRNA gene: evaluation of BACTEC 9240 instrument true-positive and false-positive results. J Clin Microbiol 39:3578–3582[CrossRef]
SaitoT.,
IinumaY.,
TakakuraS.,
FujiharaN.,
KudoT.,
IchiyamaS.2004; Can BacT/Alert FA and FN blood culture bottles increase the recovery of microorganisms in the clinical laboratory?. J Chemother 10:343–347[CrossRef]
SmithJ. A.,
BryceE. A.,
Ngui-YenJ. H.,
RobertsF. J.1995; Comparison of BACTEC 9240 and BacT/Alert blood culture systems in an adult hospital. J Clin Microbiol 33:1905–1908
VelegrakiA.,
ManousosE. K.,
SkiniotisG.,
SavalaM.,
Mitroussia-ZiouvaA.,
LegakisN. J.1999; Identification of medically significant fungal genera by polymerase chain reaction followed by restriction enzyme analysis. FEMS Immunol Med Microbiol 23:303–312[CrossRef]
ZieglerR.,
JohnscherI.,
MartusP.,
LenhardtD.,
JustH. M.1998; Controlled clinical laboratory comparison of two supplemented aerobic and anaerobic media used in automated blood culture systems to detect bloodstream infections. J Clin Microbiol 36:657–661