IMPACT OF CHLORINE INJURY ON REACTION-KINETICS OF COLIFORMS AND ESCHERICHIA-COLI IN COLISURE(TM) AND LTB

This study compared a chromogenic and fluorogenic substrate based medi um, Colisure, with the conventional fermentation based medium, lauryl tryptose broth (LTB), for the recovery of chlorine-injured and non-inj ured coliforms and E. coli. Mixed natural populations of coliforms fro m sewage, with and without chlorine exposure, and untreated surface wa ter samples were examined following a USEPA established procedure. Col isure and LTB were examined after 20, 24, 28 and 48h incubation and re actions verified. There were slight increases in positive reactions ov er time with unchlorinated samples, for which the two media gave simil ar kinetic patterns. The increases over time with chlorinated samples were much greater than with unchlorinated samples. LTB gave significan tly lower total positive responses and had a more pronounced lag perio d than did Colisure. Total coliform bacteria from surface water sample s gave somewhat different reactions with more of an increase with time . Colisure recovered comparable or higher numbers of total coliforms a nd E. coli in 20-28h than LTB after 48h. These results confirm that Co lisure gives improved recovery of chlorine-injured total coliforms and E. coli under conditions simulating treated drinking and source water , resulting in a more realistic estimate of the actual population of i ndicator bacteria in public water supplies. (C) 1997 IAWQ. Published b y Elsevier Science Ltd.