Question
Bacteroides fragilis is the most frequent cause of anaerobic bacteraemia. Although recent data suggest a rise in resistance to antibiotics commonly recommended for therapy of this and other anaerobic bacteria, surveillance on antimicrobial resistance (AMR) remains limited due to a lack of both data availability and comparability. However, a newly introduced standardised method for antimicrobial susceptibility testing (AST) of anaerobic bacteria has made larger scale surveillance possible for the first time. Thus, a European multicentre study was initiated to investigate phenotypic AMR of Bacteroides fragilis isolates from bacteraemia across Europe in 2022.
Methods
Clinical microbiology laboratories in Europe were invited to contribute results of antimicrobial susceptibility testing (AST) for blood culture isolates identified as Bacteroides fragilis (per unique patient per year of observation (2022)). Antimicrobial susceptibility testing was performed locally by all participating laboratories in a prospective or retrospective way, using the EUCAST disc diffusion method on Fastidious Anaerobe Agar with 5% mechanically defibrinated horse blood (FAA-HB).
Results
A total of 16 European countries (14 EU plus Switzerland and Israel) reported 449 unique isolates of Bacteroides fragilis from blood for which AST had been performed (out of a total 602 unique isolates). Clindamycin showed the highest resistance rates (20.9%, range 0 - 63.6%), followed by piperacillin-tazobactam (11.1%, 0 - 54.5%), meropenem (13.4%, 0 - 45.5%), and metronidazole (3.1%, 0 - 40.0%), all with wide variation between countries.
Conclusions
Considering the regional differences (unexpectedly high resistance rates in some countries particularly in Southern Europe) and the mean resistance rates across Europe (above 10% for three of the four anti-anaerobic antibiotics included), both local AST of clinically relevant isolates of Bacteroides fragilis and continued surveillance on an international level is warranted.