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Appl Environ Microbiol. 1969 October; 18(4): 562-565
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Occurrence of False-Positive Most Probable Number Tests for Fecal Streptococci in Marine Waters¹

^a Biological Sciences Group, Microbiology Section and Marine Research Laboratory, University of Connecticut, Storrs, Connecticut 06268

ABSTRACT

By the use of the most probable number technique with azide dextrose and ethyl violet azide broths for enterococci, the common occurrence of false-positive tests was noted when marine and estuarine waters were sampled. Organisms isolated included a marine bacterium, gram-positive and gram-negative nonmarine bacteria, and yeasts. All cultures were capable of growth in azide-dextrose, ethyl violet-azide, and KF broths. Representative isolates grew in media containing 0.08% NaN₃. The tentatively accepted most probable number method for fecal streptococci is thus of dubious value in assessment of sewage pollution levels in estuarine waters. All positive tubes must be examined microscopically for the presence of nonstreptococcal forms.

¹ Contribution no. 56 from the University of Connecticut Marine Research Laboratory, Noank, Conn. 06340. Presented in part at the 69th Annual Meeting of the American Society for Microbiology, Miami Beach, Fla., 4-9 May 1969.