Long-Term Effects of Residual Chlorine on Pseudomonas aeruginosa in Simulated Drinking Water Fed With Low AOC Medium

Abstract

Residual chlorine is often required to remain present in public drinking water supplies during distribution to ensure water quality. It is essential to understand how bacteria respond to long-term chlorine exposure, especially with the presence of assimilable organic carbon (AOC). This study aimed to investigate the effects of chlorination on Pseudomonas aeruginosa in low AOC medium by both conventional plating and culture-independent methods including flow cytometry (FCM) and quantitative PCR (qPCR). In a simulated chlorinated system using a bioreactor, membrane damage and DNA damage were measured by FCM fluorescence fingerprint. The results indicated membrane permeability occurred prior to DNA damage in response to chlorination. A regrowth of P. aeruginosa was observed when the free chlorine concentration was below 0.3 mg/L. The bacterial response to long-term exposure to a constant low level of free chlorine (0.3 mg/L) was subsequently studied in detail. Both FCM and qPCR data showed a substantial reduction during initial exposure (0–16 h), followed by a plateau where the cell concentration remained stable (16–76 h), until finally all bacteria were inactivated with subsequent continuous chlorine exposure (76–124 h). The results showed three-stage inactivation kinetics for P. aeruginosa at a low chlorine level with extended exposure time: an initial fast inactivation stage, a relatively stable middle stage, and a final stage with a slower rate than the initial stage. A series of antibiotic resistance tests suggested long-term exposure to low chlorine level led to the selection of antibiotic-resistant P. aeruginosa. The combined results suggest that depletion of residual chlorine in low AOC medium systems could reactivate P. aeruginosa, leading to a possible threat to drinking water safety.

Comparing the anti-bacterial performance of chlorination and electrolysis post-treatments in a hand washing water recycling system

“…The work of Mao et al. (2018) presents a similar investigation of long-term changes in TCC and ICC due to chlorination.…”

“…Pseudomonas aeruginosa inactivation was conducted in pure culture, while our study utilized a community of bacteria. The presence of a community of bacteria introduces the possibility that some bacteria in our system may be inactivated in chlorine at faster, comparable, or slower rates than the Pseudomonas aeruginosa tested by Mao et al. (2018).…”

Biofilm Microbiome (Re)Growth Dynamics in Drinking Water Distribution Systems Are Impacted by Chlorine Concentration

“…Of particular relevance is understanding how the effect of chlorine upon biofilms may change through a network as the residual decays and the concentration changes. Previous studies have predominantly investigated the influence of disinfectants upon the planktonic bacterial community ( Gomez-Alvarez et al, 2012 ; Wang et al, 2014b ; Li et al, 2018 ; Mao et al, 2018 ; Potgieter et al, 2018 ). A few studies have assessed biofilms in simulated distribution systems and reported the microbiome to be influenced by the type of disinfectant used (chlorine or chloramines) but the hydraulics and scale of these systems ( Santo Domingo et al, 2003 ; Wang et al, 2014a ) are not representative of operational DWDS.…”

Effect of Chlorination on Microbiological Quality of Effluent of a Full-Scale Wastewater Treatment Plant

“…Moreover, Pang et al [ 8 ] reported that Pseudomonas and Clostridium were among the most persistent taxa when secondary effluent was treated with 5 mg Cl 2 /L. Acidovorax and Pseudomonas are common denitrifies that inhabit activated sludge with a known ability to resist chlorination [ 33 , 34 , 35 ], indicating that such taxa can be effectively adapted to the oxidative action of hypochlorite. Multiple layers of extracellular polymeric substances (EPS) and biofilm formation are key parameters in the adaptation of such taxa, since the penetration of the disinfectant is prevented [ 36 ].…”