Boric acid lactose broth as a medium for the detection of fecal coliform bacteria.

Boric acid lactose broth has been suggested (Levine et al., 1934; Vaughn and Levine, 1935; Vaughn et al., 1951; Levine et al., 1955) as a medium for the detection of Escherichia coli in water and in foods. This medium is designed to suppress Escherichia freundii and species of Aerobacter, organisms often considered to be nonfecal in origin. The published results are rather convincing where separate isolates of "coliforms" are used as inocula. When isolates from agar slants are inoculated into standard lactose broth and into boric acid lactose broth (hereafter to be termed SLB and BALB, respectively), E. coli is reported to grow and to produce gas within 48 hr in both media, but Aerobacter spp. and E. freundii only in the SLB. Used as Levine and co-workers (1955) suggest, the medium should prove valuable. A positive BALB test would be definitely positive for E. coli. But does a negative test indicate the absence of E. coli or of fecal coliforms? Escherichia coli as delimited in Bergey's Mllanual of Determinative Bacteriology (Breed et al., 1948) and "fecal coliforms" are not synonymous. Skinner and Brudnoy (1932) have shown that more than 10 per cent of the Escherichia strains isolated from human feces were described in Bergey's Mllanual of Determinative Bacteriology (Breed et al., 1948) as E. freundii. A medium may be inhibitory to the organisms Inot desired, but such an agent may still inhibit many or most of the cells of the desired species. It is not at all uncommon for a medium to support growth when mass inoculations of cells are made (such as loop transfers from agar slants), but to be inihibitory when one or onily a few cells are inoculated. Whether Escherichia from feces utilizes citrates or not is beside the point. If an organism is in considerable numbers in fresh human feces and is isolated from the 104, 105, or 106 dilutions, it is "fecal" and has sanitary significance. It was to determine whether BALB will allow the dev-elopment of all the living fecal coliforms, or at least as many as the SLB allows, that this work was undertaken.