Pseudomonas aeruginosa is a common biofilm-forming Gram-negative bacterium often found in soil and ground water. It can cause diseases especially of the lungs, including pneumonia. Nevertheless, it is an opportunistic pathogen which can cause a wide range of infections in almost any organ or tissue, particularly in patients with a weakened immune system, such as cancer patients, newborn and those with severe burns, diabetes mellitus or cystic fibrosis (DH, Estates & Facilities, 2013).
Pseudomonas aeruginosa is known to thrive particularly well where it has access to a higher level of oxygen and the temperature is between 11-44˚C, although some strains are able to multiply at just 4˚C.
A collaborative study between ProEconomy Ltd and University College London (UCL) included a lab study to evaluate the inactivation of P. aeruginosa when exposed to increasing levels of copper and silver ions generated by ionization.
Materials and Methods
ProEconomy provided the Orca copper and silver ionization (CSI) system to UCL for their Master’s degree students to carry out the study.
The experiment was divided into two parts. The first part was the preparation and maintenance of Pseudomonas aeruginosa. The selected strain was collected from the -80℃ frozen stock, and transferred onto an agar plate and incubated at 37℃ for 24 hours. A small number of colonies were suspended in 40 ml LB broth medium and incubated at 37℃ for 16 hours and the absorbance was adjusted to 0.08.
The second part of the experiment was the inactivation of P. aeruginosa by CSI. Water from the Orca CSI system containing known concentrations of copper and silver ions (0.2/0.02 mg/L, 0.4/0.04 mg/L and 0.6/0.06 mg/L, respectively) was mixed with growing P. aeruginosa culture in plates and incubated for up to a total of 24 hours. Tap water and de-ionised (DI) water were used as controls. The sampling times were set at 0, 1, 3, and 24 hours.
The starting concentration of P. aeruginosa colonies growing in the plates ranged from 1.2 x 10^7 cfu/ml to 1.5 x 10^8 cfu/ml. The results are shown in Figure 1 and it can be observed that over 82% of cells exposed to copper and silver ions stopped growing, decreasing from an initial 102 colonies to 18 colonies after 24 hours when exposed to the highest copper/silver ions concentrations (0.6/0.06 mg/L copper/silver). The respective results for 0.4/0.04 mg/L and for 0.2/0.02 mg/L were 77% and 40%.
Figure 1 – P. aeruginosa inactivation with time when exposed to different copper/silver concentrations.
In tap water, the concentrations of P. aeruginosa cells increased with time, from 1.0 x 10^8 to 8.2 x 10^8 cfu/ml after 24 hours (Figure 2). No growth was observed in DI water as there was no food source for the bacteria to use.
The effectiveness of CSI can be observed at the preliminary stages of the experiments, with an 82% reduction in P. aeruginosa cells growth after 24 hours exposure to copper and silver ions. Considering the initial numbers of P. aeruginosa colonies were very high, this is very good inactivation by the CSI system. The study is still ongoing, and the results will be published in a paper at a later stage.
By guest blogger Dr Vera Barbosa
DH, Estates and Facilities (2013). HTM 04-01 – Addendum: Pseudomonas aeruginosa – advice for augmented care units. 37 pp. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/140105/Health_Technical_Memorandum_04-01_Addendum.pdf