Isolation of anaerobic bacteria of the Bacteroides fragilis group from environmental samples

Abstract

The aim of this study was to analyze the effectiveness of identification of Bacteroides fragilis group (BFG) strains isolated from human and rat feces, hospital wastewater, and untreated and treated sewage from a wastewater treatment plant (WWTP). BFG strains were plated on Bacteroides Bile Esculin (BBE) agar. Characteristic colonies were isolated from the culture medium, tested for antibiotic resistance and identified by PCR and MALDI-TOF MS. A total of 319 strains that formed characteristic colonies were isolated from BBE agar, of which 250 were resistant to kanamycin, colistin and vancomycin. PCR revealed that only 135 strains harbored the bfr gene specific to the BFG. In MALDI-TOF MS analysis, only 123 isolates were classified as members of the BFG. The most frequently isolated species was Parabacteroides distasonis (51.22% of strains). B. fragilis, B. ovatus and B. thetaiotaomicron were less frequently encountered in the analyzed environmental samples (30.01%, 8.13% and 5.69%, respectively). The strains isolated from human and rat feces on BBE agar were most reliably identified, and 100% of the isolated strains were classified as members of the BFG. The effectiveness of isolation of BFG strains from hospital wastewater and untreated and treated sewage from the WWTP was relatively low (20%, 19%, 40%, respectively). The results of this study suggest that the method for isolating BFG strains from environmental samples on BBE agar requires modification. Additional methods, such as PCR and MALDI-TOF MS, can be used to more effectively identify BFG strains isolated from different environmental samples.