AllsopK.&SticklerD. J. 1984. The enumeration of Bacteroides fragilis group organisms from sewage and natural waters.Journal of Applied Bacteriology56, 15–24.A membrane filtration technique has been developed for the enumeration ofBacteroides fragilisgroup (BFG) organisms from sewage and natural waters. The method uses the agar medium of Wilkins and Chalgren supplemented with gentamicin. penicillin, aesculin and ferric ammonium citrate. Membrane filters with 0.22 μm pores were significantly more efficient than those with 0.45 μm pores in the isolation of BFG. A preliminary incubation period of 4 h at 30d̀C prior to 44 h at 37d̀C yielded significantly higher numbers of BFG than direct incubation at 37d̀C fo