Influence of copper on the viability of Pseudomonas aeruginosa and its role in the transition into the viable but nonculturable state
Copper is commonly used as a material in domestic plumbing systems and is known to have an inhibitory effect on bacteria. This has been shown for a variety of different Gram-positive and Gram-negative bacteria (e.g. Escherichia coli, Pseudomonas aeruginosa, Listeria monocytogenes). In the past toxicity levels were determined by examining bacterial growth in the presence of various concentrations of copper. A lack of growth is considered to indicate that copper has killed cells, without considering the possibility that cells could enter the "viable but nonculturable" (VBNC) state as a survival strategy against copper stress.
Copper as a chemical inducer of the VBNC state in bacteria has been investigated for various plant-pathogenic bacteria (e.g. Rhizobium leguminosarum, Erwinia amylovora) and for the human pathogen Escherichia coli. But less is known for the target organism Pseudomonas aeruginosa.
Pseudomonas aeruginosa, a Gram-negative rod bacterium, is a causative agent of waterborne pneumonia and presents high tolerance against conventional disinfectants. It can be found in higher frequency in household-installations, which may pose a thread espeacially to immunocompromised persons. Furthermore, this microorganism is known to be able to enter the VBNC state and thus will not be detected by conventional culture methods.
In this project the influence of copper on the viability of Pseudomonas aeruginosa and its role as a chemical inducer of the VBNC state will be investigated using various molecular biological methods. Viability will be determined by cultivation as well as by direct viable count, membrane integrity determination, respiration activity determination and PNA-FISH.
The phenomenon of copper as an inducer of VBNC may be of hygienic relevance for risk assessment of P. aeruginosa occurring in plumbing systems made of copper material.