An improved formate lactose glutamate medium for the detection ofEscherichia coliand other coliform organisms in water

Abstract

A chemically defined fluid medium—improved formate lactose glutamate—is described of which the cost is less than a quarter that of standard MacConkey broth and which is at least equally suitable for routine bacteriological examination of water. It has actual advantages in that the medium after fermentation is clearer and that, therefore, acid and gas production is more easily seen; moreover more isolations of both coliform bacteria and ofEsch. coliare obtained with fewer false positive reactions. Trials with a solid version of the medium suggest that the relative freedom from false positive reactions arises from the failure of the medium to growCl. welchii—one of the commonest causes—and enterococci, another suspected participant. In fact, without any inhibitory agent the medium appears to be virtually specific for the coliform group and particularly favoursEsch. coli.It remains to be seen whether certain aerobic spore-bearers found from time to time in surface waters may, to some slight extent, interfere with the almost complete specificity so far discovered.The medium is recommended in place of MacConkey broth and other peptonecontaining media, not only for the prospect of better results, in that suppression of the coliform group does not occur, but also for cheapness and for freedom from the inevitable variability associated with media incorporating peptone and, particularly, bile salt. It is hoped that this medium will shortly become available commercially in dehydrated form at a price still considerably less than that required to make up MacConkey broth from its constituents.Some labour-saving curtailments in the routine of water examination are also suggested.It is hoped not only that the fluid medium will supplant MacConkey broth for the dilution method of water analysis but that the solid medium, without material alteration, will also prove suitable for water examination by membrane filtration.I am deeply grateful to my laboratory staff, particularly Mr J. H. Evans, F.I.M.L.T., and Mr G. H. Lowe, F.I.M.L.T., for undertaking so much of the work when routine work was particularly heavy, and for many valuable suggestions. My thanks in addition are due to Mrs Peggy Johnson and Mrs Marilyn Childs, who made up the medium, and also to the directors of the participating P.H.L.S. laboratories not only for having the work carried out but for helpful comments.

The preparation of simulated water samples for the purpose of bacteriological quality control

“…Single strength improved formate lactose glutamate medium (Gray, 1964) with the lactose, thiamine and indicator omitted (I.F.L.G. LAC-) plus 1'8 % boric acid was the medium used.…”

“…For this purpose it was necessary to find some means whereby suspensions of coliform organisms and Escherichia coli could be kept relatively stable in number at room temperature for a period of 7-10 days. This, it was finally found, was best achieved by adding selected strains of the organisms to improved formate lactose glutamate medium (Gray, 1964) without the lactose but with added boric acid to a final concentration of 1.8 %.The procedures adopted in the successful quality control programme are described. …”

Single tube confirmatory tests forEscherichia coli

“…In contrast, in preliminary work, standard lauryl tryptose lactose broth sometimes failed to give positive indole reactions at 44 'C in tests with pure cultures of Escherichia coli, as also occurred with the tryptone lactose ricinoleate broth of Mara (1973). As an alternative, the PHLS Water Committee in previous unpublished work with a selective medium of a quite different type -the chemically defined, minerals-modified version of Gray's improved formate lactose glutamate medium (Gray, 1964;PHLS, 1969) -found that this, with the addition of tryptophan, also showed promise as a single tube confirmatory medium.…”

A comparison between minerals-modified glutamate medium and lauryl tryptose lactose broth for the enumeration of Escherichia coli and coliform organisms in water by the multiple tube method

“…In Britain, the usual surfactants were bile salts as in MacConkey broth -or more recently Teepol broth (Jameson & Emberley, 1956). These were used almost exclusively in the multiple tube test for these organisms until Gray (1964) developed an improved formate lactose glutamate medium (IFLG). This chemically defined medium, which was based on earlier work (Folpmers, 1948;PHLS, 1958;Gray, 1959) and designed exclusively for the isolation of coliform organisms and E. coli in water, was found in trials to be better than either MacConkey or Teepol broth (PHLS, 1968), and it was therefore recommended for routine use (Report, 1969).…”