Anaerobic bacteria from bloodstream infections: Comparison of three methods for identification and detection of the antibacterial susceptibilities of recovered isolates

Abstract

Abstract This study was aimed at the comparison of three different methods used for the identification of anaerobic bacteria isolated from blood cultures and the determination of the antibacterial susceptibilities of the isolates. The study material comprised of 5282 blood samples. The samples were incubated in a BacT/ALERT system. The species identification of the isolates was performed using BBL Crystal Anaerobe system, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), and 16S rRNA gene sequence analysis. Antibacterial susceptibility testing was performed using the disk diffusion method with benzylpenicillin, clindamycin, piperacillin-tazobactam, meropenem, and metronidazole disks. In the BacT/ALERT system, forty-five anaerobic bacterial isolates were recovered from 39 (0.74%) of the samples that showed growth signs in blood culture bottles. The BBL Crystal Anaerobe system and 16S rRNA gene sequence analyses enabled the genus and species identification of all 45 isolates (100%), whereas with MALDI-TOF MS, only 37 (82.2%) of the isolates were able to be identified. The compatibility of the three tests for the identification of the isolates at genus and species level was 62.2% (28/45) and 37.8% (17/45), respectively. Antibacterial resistance rates of the isolates to piperacillin/tazobactam, clindamycin, benzylpenicillin, meropenem, and metronidazole were detected as 100%, 73.8%, 40%, 9.8%, and 5.5%, respectively. MALDI-TOF MS showed a higher level of compatibility with 16S rRNA gene sequence analyses, compared to the BBL Crystal Anaerobe system. The high rates of susceptibility to meropenem and metronidazole suggested that these antibiotics could be safely used for the empirical treatment of anaerobic bacterial infections.