PCR evaluation of false-positive signals from two automated blood-culture systems

• Published in: Journal of medical microbiology Vol. 55; no. 1; pp. 53 - 57
• Main Authors: Karahan, Z. Ceren, Mumcuoglu, Ipek, Guriz, Haluk, Tamer, Deniz, Balaban, Neriman, Aysev, Derya, Akar, Nejat
• Format: Journal Article
• Language: English
• Published: Reading Soc General Microbiol 01.01.2006; Society for General Microbiology
• Subjects: Adult; Aged; Arthrobacter; Bacteremia - diagnosis; Bacteremia - microbiology; Bacteria - classification; Bacteria - genetics; Bacteria - growth & development; Bacteria - isolation & purification; Bacteriological Techniques - instrumentation; Biological and medical sciences; Blood - microbiology; Corynebacterium; Culture Media; DNA, Bacterial - analysis; DNA, Bacterial - isolation & purification; DNA, Fungal - analysis; DNA, Fungal - isolation & purification; DNA, Ribosomal - analysis; False Positive Reactions; Female; Fundamental and applied biological sciences. Psychology; Fungemia - diagnosis; Fungemia - microbiology; Humans; Infectious diseases; Male; Medical sciences; Microbiology; Micrococcus; Middle Aged; Pasteurella multocida; Polymerase Chain Reaction - methods; RNA, Ribosomal, 16S - genetics; Staphylococcus epidermidis; Staphylococcus hominis; Streptococcus pneumoniae; Polymerase chain reaction; Microbiology; Blood culture
• ISSN: 0022-2615; 1473-5644
• DOI: 10.1099/jmm.0.46196-0

1 , 3 Division of Paediatric Molecular Pathology and Genetics 1 and Cebeci Hospital Central Microbiology Laboratory 3 , Ankara University, School of Medicine, 06100-Cebeci, Ankara, Turkey 2 Microbiology and Clinical Microbiology Department, Ankara Numune Education and Investigation Hospital, 06100-Sihhiye, Ankara, Turkey Correspondence Z. Ceren Karahan ckarahan{at}medicine.ankara.edu.tr Received 9 June 2005 Accepted 21 September 2005 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), S taphylococcus epidermidis (2), Staphylococcus hominis (1), Micrococcus sp. (1), S treptococcus 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 CO 2 concentration. Abbreviations: ANEIH, Ankara Numune Education and Investigation Hospital; AUSM-CH, Ankara University School of Medicine-Cebeci Hospital.