Effects of chemically and electrochemically dosed chlorine on Escherichia coli and Legionella beliardensis assessed by flow cytometry

• Published in: Applied microbiology and biotechnology 2010-06, Vol.87 (1), p.331-341
• Main Authors: Wang, Yingying, Claeys, Lieve, van der Ha, David, Verstraete, Willy, Boon, Nico
• Format: Article
• Language: English
• Subjects: Applied Microbial and Cell Physiology; Bacteria; Biological and medical sciences; Biomedical and Life Sciences; Biotechnology; chlorination; Chlorine; Chlorine - chemistry; Chlorine - pharmacology; Disinfection; Disinfection & disinfectants; Disinfection - methods; Drinking water; E coli; Electrochemistry; Electrodes; Enzymatic activity; Escherichia coli; Escherichia coli - cytology; Escherichia coli - drug effects; Escherichia coli - growth & development; Flow Cytometry; Fundamental and applied biological sciences. Psychology; Laboratories; Legionella; Legionella - cytology; Legionella - drug effects; Legionella - growth & development; Life Sciences; Membranes; Microbial Genetics and Genomics; Microbial Viability - drug effects; Microbiology; Microorganisms; Physiology; Plating; Studies; VBNC; Yeast
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-010-2526-2

The present study reports the disinfection effects of chemically and electrochemically dosed chlorine on two models for typical water-borne bacteria (Escherichia coli and Legionella beliardensis) by plating and flow cytometry (FCM) in combination with different fluorescence dyes. The residual effect on various cell functions, including cultivability, esterase activity, membrane polarization, and integrity, was tested at different free chlorine concentrations. In comparison, chemical disinfection yielded on average 60% more E. coli cells entering the viable but nonculturable (VBNC) state than electrochemical disinfection. Here, VBNC is defined as those cells with intact cell membrane but which cannot be cultured on solid nutrient agar plates. L. beliardensis was about five times more resistant to chlorine disinfection than E. coli. The results also suggested the two methods result in different disinfection mechanisms on L. beliardensis, i.e., chemically dosed chlorine targeted cell membrane integrity before enzyme activity, while electrochemically dosed chlorine acted the other way round. In addition, both bacteria lost the integrity of their cell membranes at three times lower chlorine concentration over a longer contact time (i.e., 40 vs. 10 min) by the chemical method. Our results showed that FCM is an appropriate tool to evaluate the effects of water disinfection and the percentage of cells in VBNC in a matter of hours. Electrochemical disinfection is suggested to be a favorable alternative for chemical disinfection.