Improved recovery of chlorine-stressed coliforms with pyruvate supplemented media

The use of sodium pyruvate in lauryl sulphate-based enumeration media to facilitate the recovery of chlorine-stressed coliforms was investigated as part of a programme to develop a single membrane enumeration medium for coliforms and Escherichia coli. Pyruvate degraded peroxides and promoted cell recovery. Water containing 0.1 mg free chlorine per litre was inoculated with E. coli and enumerations were made at various times with the standard medium supplemented with 0.01-1.0 per cent pyruvate. There was a 9-fold increase in recovery of bacteria from samples exposed to chlorine for 3 h with media containing 0.05 per cent pyruvate or above. Measurements on a range of chlorinated and unchlorinated water samples also demonstrated higher counts on chlorinated waters with the 0.05 per cent pyruvate-modified medium.