RESEARCH – November 2021

Spectrum and antibiotic susceptibility of anaerobic microbes diagnosed at the United Laboratories of Tartu University Hospital

Authors: Krista Lõivukene, Siiri Kõljalg, Kadri Kermes, Epp Sepp, Paul Naaber

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Objective. The aim of our study was to describe the species distribution and to determine changes in the resistance profile of anaerobic bacteria isolated at Tartu University Hospital. Methods. We analysed retrospectively data from the Laboratory Information System for 2016 and 2020. All strains were identified by MALDI-TOF MS, the MIC-values for the different antibiotics were determined using gradient tests (Liofilchem, Italy). Resistance was interpreted using EUCAST breakpoints.
Results. The number of anaerobic cultures increased by 29% over the four years. The proportion of positive results was similar, 9.1% and 10.4%, respectively. The most common pathogens were Gram-negative anaerobic rod-shaped bacteria (Bacteroides fragilis, Bacteroides spp. and Prevotella spp.). The incidence of Gram-positive anaerobes was relatively low over the years. We observed an increase in Clostridium spp. and in diversity in the group of Grampositive anaerobic cocci. The percentage of susceptible strains in the two years studied was similar, but there were significant
differences in the MIC values (p <0.05) of ampicillin-sulbactam, imipenem and clindamycin in Gram-negative rods, which were higher in 2020 than in 2016.
Conclusions. The diagnostics of anaerobic infections has improved at the Tartu University Hospital in the period 2016 – 2020. There is no difference in the spectrum of microbial groups, but due to the improvement of identification methods, the number of identified species has increased. The resistance pattern of anaerobes has been stable but the changes in MIC values may indicate
a further steady increase in resistance. The surveillance of antibiotic resistance of anaerobes is important to predict the efficiency of chosen empirical treatment.