Anaerobic bacteria from bloodstream infections: Identification and antibacterial susceptibility testing in a single center in Türkiye

Abstract

This study aimed the identification of anaerobic bacteria isolated from blood cultures and the determination of antibacterial susceptibility of the isolates. The study material comprised of 5,282 blood samples taken between 2018 and 2020. The samples were incubated in a BacT/ALERT system. The species identification of the isolates was performed by three methods namely, 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, 45 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. 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 are options for the empirical treatment of anaerobic bacterial infections.