Document Type

Article

Department/Program

Virginia Institute of Marine Science

Publication Date

12-1979

Journal

Applied and Environmental Microbiology

Volume

38

Issue

6

First Page

1147

Last Page

1152

Abstract

Sublethal stress in Escherichia coli was detected in various test media after exposure (in vitro) to seawater of various salinities. Stress was measured with an electrochemical detection technique and a,-galactosidase assay. Test media included EC medium, medium A-1, and tryptic soy broth modified to contain lactose for /?-galactosidase assay experiments. Stress was defined as the difference between a predicted electrochemical response time calculated for unstarved cells from a standard curve and the observed electrochemical response time for cells starved in seawater. The higher the salinity, the greater the stress for all test media examined. Stress was most pronounced in EC and was attributed primarily to initial die-off of starved cells exposed to the test medium at the elevated temperature of 44.5°C. Lag time and growth rates in test media were not significantly affected by salinity. fl-Galactosidase specific activity, assayed in starved cells after transfer to an induction medium at 44.5°C for 150 min, was inversely related to the salinity of the starved cell suspension. The consequences of these observations with respect to coliform enumeration methods are discussed.

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