Introduction

Antibiotic resistant micro-organisms like Carbapenemase Producing Enterobacteriaceae (CPE) and Vancomycin Resistant Enterococci (VRE) are commonly found to be in drains in the healthcare environment. These resistant bacteria collect in drains and thrive in the formation of biofilms, due to drains being the perfect environment for growth. Eradicating these from the drains is proving to be a difficult task, with usual disinfection techniques not able to penetrate the biofilm.

Micro-organisms overview

VRE are enterococci that are resistant to the antibiotic Vancomycin.

CPE are gram negative bacteria that produces carbapenemase enzyme that inactivates the carbapenem of antibiotics, used for treating infections.

Pseudomonas aeruginosa, a gram negative bacterium that accumulates in drains and causes infection in humans. It’s intrinsically resistant to multiple antibiotics, is an opportunistic bacterium, and results in pneumonia, septic shock, gastrointestinal infections, skin and soft tissue infections, and similar infections. P. aeruginosa is known to be persistent in the healthcare environment.

Oxidation reminder

As a quick chemistry reminder – molecules have different charge properties from electrons. It can either be polar (consisting of positive and negative charges within a molecule, like water), or non-polar (consisting of no or minimal charges, like oil). Polar and non-polar molecules, like oil and water, are immiscible, i.e. they do not mix.

Some polar molecules found in microorganisms:

Amino acids

Proteins

DNA

RNA

Sugars

Some non-polar molecules found in microorganisms:

Fats (lipids)

Disinfectants typically contain an active ingredient which will be polar (to a greater or lesser extent), and a surfactant. Surfactants are long fatty chains connected to a polar head which allows for mixing of polar and non-polar substances such as oil and water, helping to remove oils and dirt from surfaces.

You may find that when you’re washing up, the cleaning properties diminish over time. Washing up liquid contains surfactants that bind the oil from pans, baking trays etc. to a surfactant, allowing the oils to be mixed in with the water, and washed away. This property is limited by how much washing up liquid you use and the quality and type of surfactants needed, and when used up, you’ll notice that the oil doesn’t wash away as well.

Why is P. aeruginosa such an issue?

There are 2 key factors with P. aeruginosa that make it particularly difficult to kill. Firstly, it’s a gram-negative bacterium, which are notoriously more difficult to kill with disinfectants, owing to their combination of outer protection – a cell membrane and a cell wall. The cell wall consists of peptidoglycan layers. These sugar and amino acid layers have polar regions that a disinfectant can target. The cell membrane, however, consists of lipopolysaccharides. These are oily and are therefore more difficult to target with a polar disinfectant.

Secondly, P. aeruginosa has developed resistance mechanisms that have given rise to multiple strains with varying resistance to antibiotics. When a high-risk individual develops an infection, it is very difficult and expensive to treat. It leads to extended hospital stays, increased costs associated, and results in varying conditions, from sepsis to pneumonia. As an opportunistic bacterium, infant and elderly patients are at particularly high risk, along with those who have had a transplant, have catheters, are undergoing chemotherapy, and more.

Resistance mechanisms usually refer to antibiotic treatment, however it has been found that some non-oxidising disinfectants can result in similar antimicrobial resistance. For example, quaternary ammonium compounds lyse cell walls, spilling the contents of whole portions of genomes. For an opportunistic bacterium like P. aeruginosa, this can result in horizontal gene transfer, a well-known and well-documented cause of antimicrobial resistance.

The 2012 Belfast incident is well-known and should remain well-known so we can learn from its mistakes. 3 premature babies died out of a total 7 infected with P. aeruginosa, and the source was identified as sink taps. Following up from this awful incident, premature babies on neonatal wards are now bathed using sterile water. From 2020-2021 there were 4000 cases in England and Wales, of which 1600 patients died, giving a mortality rate of 40%. There are vital, life-saving decisions to be made to prevent infections and therefore deaths.

Splash zone

The splash zone consists of all the areas around a sink that could be at risk of splash or any form of contamination from P. aeruginosa. To maintain a clean and minimal risk sink area, it’s vital that we use a strongly polar disinfectant that includes an effective surfactant to help to break down the fatty layer. Chlorine disinfectants particularly struggle with P. aeruginosa because they exist as single atoms in solution, a negatively charged chlorine ion. This is completely repelled by the cell membrane as polar does not mix with non-polar. It’s also been found that chlorine reacts with surfactants because of the polar head, so it’s not too beneficial to use chlorine with a surfactant added. Using a disinfectant with peracetic acid is highly beneficial as it has a short carbon chain. i.e., it has a small, minimally polar region which allows better penetration of cells.

Why does it accumulate in drains?

P. aeruginosa doesn’t have any specific requirements for growth. It can survive in temperatures from 4-42 degrees C, and is extremely metabolically opportunistic. If there is some form of nutrient source, it can process this and use it to grow. Drains are perfect conditions for P. aeruginosa as they have a constant nutrient source in soaps, oils, soil and broken-down bacteria washed off hands. This feeds biofilm colonies and encourages rapid growth. P. aeruginosa takes up to 72 hours to incubate, meaning at every stage of testing and remedying, we are up to 3 days behind.

In addition, biofilms can be found throughout water systems. If present, P. aeruginosa will mostly be found within 2 metres of the point of delivery of water at the outlet. Off shoots of the main water system where water is not continuously running are at particular risk.

What can we do about it?

Dealing with drains is a complex and large task involving estates, facilities, domestics, clinical, engineering, maintenance, and others depending on the Trust. Drains are ubiquitous and have 2 key sides: water coming in and water and waste going out. Typically, a Trust has control from the central hospital source. Currently water is treated in a chlorination process which uses a low ppm of chlorine to disinfect water. Low strength chlorine does not break down biofilms and accumulation of these in water systems and these are required to be treated. Speak to your Water Decontamination Team for more information. A Trust should have policies outlining what can and cannot be put down the drain, how to clean outlet drains, and what disinfectant should be used at what frequency in this process.

Actions

There are actions a Trust can take to help to prevent P. aeruginosa outbreaks. Besides infrastructure changes and commissioning new builds, actions relating specifically to disinfection include:

1. Don’t use quaternary ammonium products around any drains (including showers, handwash sinks, toilets, specialist equipment such as burns mattresses)

2. Don’t rinse quaternary ammonium products down any drains

3. Use a chlorine-free oxidiser like peracetic acid to ensure high-level disinfection including AMR P. aeruginosa

4. Consider transferring water treatments from chlorination to use a more effective biocide like peracetic acid (commonly used in water treatment, food, and agricultural industries)

5. Perform traceability exercises to locate the source of an outbreak

6. Refer to updates of guidance documents including HTM 04-01

7. Audit cleaning processes, remembering the clinical staff in the process

8. Explain the importance of cleaning splash zones to prevent P. aeruginosa outbreaks

9. Use the National Standards of Healthcare Cleanliness to support decision-making

Further Reading and References

Impact of sink design on bacterial transmission - https://www.sciencedirect.com/science/article/pii/S0195670122001347

CRE – A menace to our most vulnerable patients - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3960994/

The role of water in healthcare-associated infections - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5583640/

Authors:

Liam Grimshaw (BSc (Hons), MSc by research)

Callum Close (BSc (Hons))