Swimming pools are commonly treated
with chlorine, which reacts
with the natural organic matter and organic matter introduced by swimmers
and form disinfection byproducts (DBPs) that are associated with respiratory-related
issues, including asthma, in avid swimmers. We investigated a complementary
disinfectant to chlorine, copper–silver ionization (CSI), with
the aim of lowering the amount of chlorine used in pools and limiting
health risks from DBPs. We sampled an indoor and outdoor pool treated
with CSI-chlorine during the swimming season in 2017–2018 and
measured 71 DBPs, speciated total organic halogen, in vitro mammalian cell cytotoxicity, and N-acetyl-l-cysteine (NAC) thiol reactivity as a cytotoxicity predictor. Controlled,
simulated swimming pools were also investigated. Emerging DBP concentrations
decreased by as much as 80% and cytotoxicity decreased as much as
70% in the indoor pool when a lower chlorine residual (1.0 mg/L) and
CSI was used. Some DBPs were quantified for the first time in pools,
including chloroacetaldehyde (up to 10.6 μg/L), the most cytotoxic
haloacetaldehyde studied to date and a major driver of the measured
cytotoxicity in this study. Three highly toxic iodinated haloacetic
acids (iodoacetic acid, bromoiodoacetic acid, and chloroiodoacetic
acid) were also quantified in pools for the first time. We also found
that the NAC thiol reactivity was significantly correlated to cytotoxicity,
which could be useful for predicting the cytotoxicity of swimming
pool waters in future studies.
Neutrophils generate hypochlorous acid (HOCl) and related reactive chlorine species as part of their defence against invading microorganisms. In isolation, bacteria respond to reactive chlorine species by upregulating responses that provide defence against oxidative challenge. Key questions are whether these responses are induced when bacteria are phagocytosed by neutrophils, and whether this provides them with a survival advantage. We investigated RclR, a transcriptional activator of the rclABC operon in Escherichia coli that has been shown to be specifically activated by reactive chlorine species. We first measured induction by individual reactive chlorine species, and showed that HOCl itself activates the response, as do chloramines (products of HOCl reacting with amines) provided they are cell permeable. Strong RclR activation was seen in E. coli following phagocytosis by neutrophils, beginning within 5 min and persisting for 40 min. RclR activation was suppressed by inhibitors of NOX2 and myeloperoxidase, providing strong evidence that it was due to HOCl production in the phagosome. RclR activation demonstrates that HOCl, or a derived chloramine, enters phagocytosed bacteria in sufficient amount to induce this response. Although RclR was induced in wild-type bacteria following phagocytosis, we detected no greater sensitivity to neutrophil killing of mutants lacking genes in the rclABC operon.
Cystic fibrosis (CF) disease is characterized by lifelong infections with pathogens such as
Staphylococcus aureus
, leading to eventual respiratory failure. Small colony variants (SCVs) of
S. aureus
have been linked to worse clinical outcomes for people with CF.
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