Antimicrobial Susceptibility Patterns and Wild-Type MIC Distributions of Anaerobic Bacteria at a German University Hospital: A Five-Year Retrospective Study (2015-2019)

Abstract

Local antimicrobial susceptibility surveys are crucial for optimal empirical therapy guidelines and for aiding in antibiotic stewardship and treatment decisions. For many laboratories, a comprehensive overview of local antimicrobial susceptibility patterns of anaerobic bacteria is still lacking due to the long incubation time and effort involved. The present study investigates the antimicrobial susceptibility patterns and related clinical and demographic data of 2856 clinical isolates of anaerobic bacteria that were submitted for analysis to the Institute for Medical Microbiology and Hygiene of the Freiburg University Medical Center (a tertiary university medical center in Southern Germany) between 2015 and 2019. Antimicrobial susceptibility testing has been carried out according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guideline. Minimum inhibitory concentration (MIC)₅₀ and MIC₉₀ for penicillin, metronidazole, moxifloxacin, and clindamycin were established for Gram-positive anaerobes and for ampicillin-sulbactam, meropenem, metronidazole, moxifloxacin, and clindamycin for Gram-negative anaerobes. The distribution of MIC-values for various antibiotics against anaerobic bacteria was also established, especially for those having no specific breakpoints according to EUCAST guidelines. Most clinically relevant anaerobic bacteria originated from general surgery, neurological, and orthopedic wards. A high proportion of isolates were resistant to moxifloxacin and clindamycin indicating the importance of their susceptibility testing before administration. Based on our study metronidazole and other β-lactam/β-lactamase inhibitor combinations such as ampicillin-sulbactam remain suitable for empirical treatment of infections with anaerobic bacteria.

Keywords: ECOFFinder; EUCAST; Germany; anaerobic bacteria; antibiotic resistance; drug susceptibility testing; epidemiologic cut-off value (ECV); wild-type cutoff value.

Figure 1

Heatmap of the isolate number of anaerobic bacteria distributed across (a) wards or (b) samples. The color represents normalized Z-score value where higher scores indicate higher number of isolates.

Figure 2

Percentage of susceptibility of selected antibiotics against tested (A) Gram-positive and (B) Gram-negative anaerobes.

Figure 3

Estimation of wild-type minimum inhibitory concentration (MIC) distributions and ECOFFs for rifampicin against Cutibacterium.

Figure 4

Estimation of wild-type MIC distributions for moxifloxacin against (A) Gram-positive and (B) Gram-negative bacteria.