Rapid detection of antimicrobial susceptibility of the Bacteroides fragilis group by flow cytometry: A preliminary study.

A total of nine Bacteroides fragilis group strains and B. fragilis ATCC 25285 were studied. Six antibiotics were used in the study. Broth dilution method was used for flow cytometry (FCM) analysis. Cell suspensions with antibiotics and antibiotic-free were stained with thiazole orange and propidium iodide (PI) to differentiate dead/live cells. The percentage of dead and live cells was calculated using FCM device. Cut-off values for antibiotics (26,7 %, 35,5 % and 30,2 % for meropenem, AMC and clindamycin, respectively) were calculated for dead/live cell differentiation. A common cut-off value was calculated for bactericidal and bacteriostatic (31,8 % and 25,7 % respectively). The PI staining ratios of the B. fragilis ATCC 25285 calculated in the MIC ranges for each antibiotic were under the cut-off values calculated with clinical isolates. The cut-off values we calculated are compatible with MBC rather than MIC values. The FCM method is one of the candidate methods for antimicrobial susceptibility testing.