Suggested Procedures for the Presumptive Test in the Determination of the Coli-Aerogenes Group

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Abstract
Results are presented comparing the efficiency of standard lactose broth, brilliant green-bile (5%) broth, and brilliant green-bile (2%) broth. With raw waters the ratio of efficiency was, respectively, 100, 90.1 and 84.2%; with effluent waters, 100, 35.0 and 36.9%. These ratios are in good agreement with those obtained by others. This would indicate that brilliant green-bile broth is unsuitable for use as a presumptive medium. Considerations for and against use of brilliant green-bile-lactose broth as a confirmatory medium are presented. The parallel planting procedure designed to combine the advantages of Standard Methods and brilliant green-bile-lactose broth is also discussed, and it is believed that the evidence presented leaves no room to hope that this procedure can ever be employed. Results are also presented comparing the efficiency of the new Dominick and Lauter media with standard lactose broth, in detecting members of the coli aerogenes group. Results indicate that this medium is even more inhibitive than brilliant green-bile. A careful study of the results of others further discloses the inhibitive nature of this medium,. Criticism of the standard lactose broth presumptive test is recognized, and steps are mentioned which should reduce the number of false presumptives by increasing the number of confirmations.

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