Abstract
Detection and identification of anaerobic bacteria in blood cultures (BC) is a well-recognized challenge in clinical microbiology. We studied 100 clinical anaerobic BC isolates to evaluate the performance of BacT/ALERT-FN, -FN Plus (BioMérieux), BACTEC-Plus and -Lytic (Becton Dickinson BioSciences) BC bottles in detection and time to detection (TTD) of anaerobic bacteria. BACTEC Lytic had higher detection rate (94/100, 94%) than BacT/ALERT FN Plus (80/100, 80%) (p<0.01) in the studied material. There was no significant difference in detection of anaerobic bacteria among the remaining bottle types. The 67 anaerobic bacteria that signalled positive in all four bottle types were analyzed to compare the time to detection (TTD) and isolates were directly identified by MALDI-TOF MS. There was a significant difference in TTD among the four bottle types (p<0.0001). The shortest median TTD was 18 h in BACTEC Lytic followed by BacT/ALERT FN (23.5 h), BACTEC Plus (27 h) and finally BacT/ALERT FN Plus (38 h) bottles. In contrast, MALDI-TOF MS performed similarly in all bottle types with accurate identification in 51/67 (76%) BacT/ALERT FN, 51/67 (76%) BacT/ALERT FN Plus, 53/67 (79%) BACTEC Plus and 50/67 (75%) BACTEC Lytic bottles. In conclusion, BACTEC Lytic bottles have significantly better detection rates and shorter TTD compared to the three other bottle types. The anaerobic BC bottles are equally suitable for direct MALDI-TOF MS for rapid and reliable identification of common anaerobic bacteria. Further clinical studies are warranted to investigate the performance of anaerobic BC bottles in detection of anaerobic bacteria and identification by direct MALDI-TOF MS.
Highlights
Anaerobic bacteraemia is associated with a mortality rate of 15–30% and accounts for 1–17% of all positive blood cultures (BC) depending on the clinical setting [1]
400 anaerobic BC bottles were included in the study, comprising four sets of different BC bottles inoculated with the same 100 anaerobic bacteria
During 5 days incubation, 89/100 (89%) BacT/ALERT FN, 80/100 (80%) BacT/ALERT FN Plus, 85/100 (85%) BACTEC Plus and 94/100 (94%) BACTEC Lytic bottles signalled positive in the BC systems
Summary
Anaerobic bacteraemia is associated with a mortality rate of 15–30% and accounts for 1–17% of all positive blood cultures (BC) depending on the clinical setting [1]. Recognition and appropriate treatment of anaerobic bacteraemia are decisive in order to improve the prognosis [2,3]. It was shown that antimicrobial therapy was altered for 56% of the patients with a positive anaerobic blood culture [4]. Detection and identification of anaerobic bacteria in BC is a well-recognized challenge in clinical microbiology. This may be explained by the fact that these microorganisms are typically fastidious, slow growing and difficult to culture. The developments of automated BC systems and anaerobic BC bottles have improved the detection of these microorganisms [3,5,6]
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