Aims. This study aimed to investigate the physiological responses of two gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and two gram-positive bacteria (Enterococcus faecalis and Bacillus sphaericus) to ultraviolet (UV) and chlorine disinfection. Methods and Results. Bacterial inactivation by UV and chlorine disinfection were evaluated with a plate count method for culturability, FCM and PMA-qPCR for membrane integrity and DyeTox13-qPCR for enzymatic activity, respectively. Both UV and chorine disinfection caused complete loss of culturability while membrane integrity remained intact after UV disinfection. Both DyeTox13-qPCR and PMA-qPCR showed high ΔCt values up to 8.9 after chlorine disinfection, indicating that both methods were able to distinguish non-treated from chlorine-treated cells. Although PMA-qPCR could not differentiate membrane integrity of cells on UV exposure, DyeTox13-qPCR showed significant differences in Δ Ct values of 5.05 and 10.4 for gram-negative (E. coli) and gram-positive (Enterococcus)...

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