Comparison of E test and Disk Diffusion Test for Antibiotic Resistance Testing of Enterotoxigenic and Non-Enterotoxigenic Bacteroides fragilis Isolated From Stools

Abstract

Background: Enterotoxigenic Bacteroides fragilis (ETBF) are one of the most important anaerobic bacteria which cause diarrhea in human beings. A bft gene is coded for enterotoxin production called fragilysin. Most of them have acquired resistance to antianaerobic bacteria agent like other facultative anaerobic bacteria. E test and different dilution methods are usually performed for antimicrobial susceptibility determination of B. fragilis. Objectives: The aims of this study are to recognize ETBF by PCR method and also to evaluate efficiency the disk diffusion method (DDM) in comparison with the E tests for antimicrobial susceptibility of B. fragilis isolates. Materials and Methods: bft gene was detected among 157 B. fragilis isolated from patients and healthy individuals by PCR. Antimicrobial susceptibility of all isolates was determined by DDM and E tests methods. Results: Nineteen (12.1%) B. fragilis containing bft gene from diarrheic (n = 14) and nondiarrheic (n = 5) feces were detected among 157 B. fragilis isolates. The highest resistance for ciprofloxacin, cefotaxim, cefoxitin with DDM and E test were 100%, 60%, and 65% respectively, while the lowest resistance in two methods was obtained for imipenem, piperacillin /tazobactam, and metronidazol. 100% agreement for some of antibiotics such as imipenem (P <= 0.05), and no correlation for others were observed among the antimicrobial susceptibility results obtained by the two methods (P >= 0.05). Conclusions: The presence of bft gene in B. fragilis isolates would not certainly result in diarrhea among patients. There is not enough accordance between DDM and Swedish E tests for antimicrobial susceptibility of B. fragilis for some antibiotics, although in other cases a good agreement was observed.