title: Performance of two blood culture systems to detect anaerobic bacteria. Is there any difference?
abstract: We studied the performance characteristics of two blood culture (BC) bottles/systems, (i) BacT/ALERT-FN Plus/3D (bioMérieux, Marcy l'Étoile, France) and (ii) BACTEC-Lytic/9000 (Becton Dickinson, Sparks, USA) for detection of growth and time-to-positivity (TTP) against a balanced and diverse collection of anaerobic bacterial strains (n = 48) that included reference strains (n = 19) and clinical isolates (n = 29) of 32 species (15 Gram-negative and 17 Gram-positive). Standard suspension of bacteria was inoculated to each bottle in duplicates and incubated in the corresponding system. Overall, 62.5% (n = 30) of strains were detected by both BC bottle types. Comparing the two, 70.8% (n = 34) and 79.2% (n = 38) of strains were detected by BacT/ALERT-FN Plus and BACTEC-Lytic bottles, respectively (p = 0.38). Among Gram-negative anaerobes (n = 25) the detection rate was 76.0% (n = 19) vs. 92.0% (n = 23) (p = 0.22), respectively. Among Gram-positive anaerobes (n = 23) the detection rate was 65.2% (n = 15) in both bottles (p = 1). The average TTP per bottle was calculated only for the strains detected by both systems (n = 30) and was 40.85 h and 28.08 h for BacT/ALERT-FN Plus and BACTEC-Lytic, respectively (p < 0.001). The mean difference was 12.76 h (95% CI: 6.21-19-31 h). Six anaerobic strains were not detected by any system, including Gram-negative Porphyromonas gingivalis, and five Gram-positive strains: Finegoldia magna, Peptostreptococcus anaerobius, Propionibacterium acnes, Clostridium novyi and Clostridium clostridioforme. Furthermore, Eggerthella lenta and Prevotella bivia were detected only by BacT/ALERT-FN Plus, while Prevotella disiens and Prevotella intermedia were detected only by BACTEC-Lytic bottles. There were no major differences in detection rate among clinical and reference strains. Anaerobic bacteria represent a minority of BC isolates, however, far from ideal detection rate was observed in this study for both tested bottle/system combinations. Nevertheless, in those cases where both gave positive signal, BACTEC-Lytic was superior to BacT/ALERT FN Plus with 12.76 h shorter mean TTP. Improvements of media in blood culture bottles available for detection of anaerobes are warranted.
authors.affiliation: Institute of Microbiology and Immunology, Medical Faculty, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Manica
authors.initials: M
authors.lastname: Mueller-Premru
authors.affiliation: Institute of Microbiology and Immunology, Medical Faculty, University of Ljubljana, Ljubljana, Slovenia. Electronic address: samo.jeverica@mf.uni-lj.si.
authors.forename: Samo
authors.initials: S
authors.lastname: Jeverica
authors.affiliation: Department of Infectious Diseases, University Medical Centre Ljubljana, Ljubljana, Slovenia.
authors.forename: Lea
authors.initials: L
authors.lastname: Papst
authors.affiliation: Institute of Clinical Microbiology, University of Szeged, Szeged, Hungary.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Nagy
mesh_terms: D016470:Bacteremia / Q000175:diagnosis*; D001421:Bacteria, Anaerobic / Q000302:isolation & purification*; D000071997:Blood Culture / Q000379:methods*; D006801:Humans; D012680:Sensitivity and Specificity; D013997:Time Factors
keywords: Anaerobe; Blood culture system; Detection rate; Time-to-positivity