Multidrug-resistant (MDR) Pseudomonas aeruginosa isolated from
cystic fibrosis (CF) sputum was shown to be more tolerant to the most commonly used
chlorine-based disinfecting agent in the UK, with approximately 7 out of 10 isolates surviving a residual free
chlorine (RFC) concentration of 500 p.p.m., when compared with
antibiotic-sensitive invasive P. aeruginosa from a non-CF blood culture source, where 8 out of 10 isolates were killed at a RFC concentration of 100 p.p.m. All CF isolates were killed at 1000 p.p.m.
chlorine. Additional studies were performed to examine factors that influenced the concentration of RFC from
chlorine-based (
sodium dichloroisocyanurate) disinfecting agents in contact with CF sputum and their components (bacterial cells, glycocalyx) to assess the reduction of the bactericidal activity of such disinfecting agents. Pseudomonas glycocalyx had a greater inhibitory effect of
chlorine deactivation than bacterial cells. Calibration curves demonstrated the relative deactivating capacity on RFC from clinical
soils, in the order
pus>CF sputum>
wound discharge fluid/synovial fluid>
ascites fluid>bile, where quantitatively each 1ā% (w/v) CF sputum reduced the RFC by 43 p.p.m. Sublethal stressing of P. aeruginosa with
chlorine resulted in lowered susceptibility to
colistin (Pā=ā0.0326) but not to
meropenem,
tobramycin or
ciprofloxacin. In conclusion, heavy contamination of healthcare fomites with CF sputum containing MDR P. aeruginosa may result in exhaustion of RFC, and this, combined with an increased resistance to
chlorine with such strains, may lead to their survival and increased antibiotic resistance in such environments. CF
infection prevention strategies in such scenarios should therefore target interventions with increased concentrations of
chlorine to ensure the eradication of MDR P. aeruginosa from the CF healthcare environment.