• viable but nonculturable;
  • drinking water;
  • internal plumbing;
  • hospital;
  • opportunistic pathogen


This study investigated how quickly cells of the opportunistic pathogen Pseudomonas aeruginosa recover culturability after exposure to two of the most common environmental stressors present in drinking water, free chlorine and copper ions. Viable but nonculturable (VBNC) P. aeruginosa undetected by direct culturing following exposure to free chlorine or copper ions can survive in drinking water systems, with potential to recover, multiply, and regain infectivity. Cells were exposed to copper sulfate (0.25 mg Cu2+ L−1) or free chlorine (initial dose of 2 mg Cl2 L−1) for 24 h. Despite total loss of culturability and a reduction in viability from 1.2 × 107 to 4 × 103 cells mL−1 (3.5 log), cells exposed to chlorine recovered viability quickly after the depletion of free chlorine, while culturability was recovered within 24 h. Copper ions did not depress viability, but reduced culturability from 3 × 107 to 2.3 × 102 cells mL−1 (5.1 log); VBNC cells regained culturability immediately after copper ion chelation. A comparison between direct culturing and Pseudalert, a specific enzyme-based assay, was performed. Both detection methods were well correlated in the range of 102–1010 cells L−1. However, correlations between the methods declined after exposure to copper ions.