Inactivation of Pseudomonas aeruginosa – A preliminary laboratory study

Posted on November 28, 2017

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inactivation of Pseudomonas aeruginosa

What Is Pseudomonas Aeruginosa?

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 thrives when it has access to a higher level of oxygen and the temperature is between 11-44˚C. However, some strains are able to multiply at just 4˚C.

The Inactivation of Pseudomonas Aeruginosa

A collaborative study between ProEconomy Ltd and University College London (UCL) included a lab study to evaluate the inactivation of Pseudomonas 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 in two parts. The first part was the preparation and maintenance of Pseudomonas aeruginosa. The 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. We took water from the Orca CSI system containing 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). Following this, it was mixed with growing P. aeruginosa culture in plates and incubated for a total of 24 hours. Tap water and de-ionised (DI) water were used as controls. The sampling times were 0, 1, 3, and 24 hours.

Results

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 (Figure 1). Over 82% of cells exposed to copper and silver ions stopped growing. In fact, they decrease 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%.

Inactivation of Pseudomonas aeruginosa

Figure 1P. 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). We can see no growth in DI water as there was no food source for the bacteria to use.

Inactivation of Pseudomonas aeruginosa
Figure 2. P. aeruginosa cells growth in tap water, DI water and Orca water. (0.6 mg/L copper and 0.06 mg/L silver)

Conclusion

We can observe the effectiveness of CSI at the preliminary stages of the experiments. Here, there was an 82% reduction in P. aeruginosa cell growth after 24 hours exposure to copper and silver ions. The initial numbers of P. aeruginosa colonies was very high. Therefore, this is very good inactivation of Pseudomonas aeruginosa by the CSI system. The study is still ongoing, and we will publish the results in a paper at a later stage.

By guest blogger Dr Vera Barbosa

References

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

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