Susceptibility of the Anaerobic Bacterial species Parvimonas micra, Prevotella intermedia and Prevotella nigrescens to selected Antibiotics – Then and Now

Sammanfattning: The present study evaluates the susceptibility to antibiotics of three anaerobic bacteria; Prevotella intermedia, Prevotella nigrescens and Parvimonas micra, bacterial species commonly found in root canal infections. Strains from two different time periods were tested against benzylpenicillin, amoxicillin and metronidazole. There are two collections of each bacterial species in this study. One of the collections is from 1976. Other collection includes the same bacterial species collected in recent years, (2009 to 2014). To identify all three bacteria species, the PCR (Polymerase Chain Reaction) method with species specific primers was used. To identify the minimal inhibitory concentrations (MIC) of selected antibiotics Etest strips were used according to Eucasts recommendations. The MIC values differ for P. micra, P. intermedia and P. nigrescens when exposed to the selected antibiotics. The new collection of P. micra showed higher MIC-values for amoxicillin and metronidazole than the old collection. The recent collection of P. intermedia showed higher MIC values for metronidazole compared to the old collection. On the other hand P. nigrescens showed no difference in MIC values between the two collections, although one recently isolated strain of P. nigrescens showed noticeable difference in MIC-values for benzylpenicillin and amoxicillin antibiotics compared to the old collection. The results indicate a susceptibility change for the tested antibiotics. Antibiotics susceptibility has changed during a 40 -year period for the selected bacterial species and it also shows that different strains of bacteria, although belonging to the same species, can have different susceptibility to antibiotics.