Microbes are classified into distinct groups depending on their characteristics, but there are four main groups that have the most potential to cause harm to the human body, if conditions are optimal. These are bacteria, fungi, viruses, and protozoa.1 These groups can also be known as opportunistic pathogens, as they have the ability to integrate themselves into a host, i.e. they can invade a human body and cause an infection. Bacteria are among the most rapid organisms to replicate; they can do so every 4 to 20 minutes.2 If the bacterium is pathogenic, this can lead to a rapid deterioration in the patient over a short period; hence the importance of a rapid diagnosis.
Viruses, on the other hand, are extremely clever organisms that can manipulate the host’s immune system in many ways. For example, they can alter their genetic make-up to mimic the host’s genes. This effectively ‘tricks’ a human’s immune system not to respond, so the virus has sufficient time to replicate, and cause not only a localised infection, but one that spreads throughout the body (see Figure 1).3 Not all microorganisms (microbes), of course, cause infections; some are critical for human survival.
Different transmission pathways
Transmission of pathogenic microorganisms can be through contact, air, food, and water. Over the years, healthcare facilities have put in place policies and procedures to try reduce the amount of hospital-acquired infections (HCAIs). Despite the daily efforts of healthcare personnel, 1 in 31 patients acquire an infection, if not multiple infections, on a daily basis.4 The most common HCAI is pneumonia, which can be caused by a bacterium called Pseudomonas aeruginosa (Figure 2).5
Water is a naturally occurring substance that is considered to be one of the most complex molecules known, but what makes it so complex? Water particles are composed of many different compounds – physical, chemical, and microbiological. It is when the composition of each water molecule changes that the water may become contaminated with pollutants, and thus unfit for purpose. In the healthcare sector, the utility of water plays a major role not only in patient diagnostics, but also in patient care.
Waterborne infection is a major risk associated with contaminated water, so much so that 80% of infections are caused by water.6 Out of this percentage, it is estimated that 64% of infections are healthcare-associated.7
Pseudomonas aeruginosa
Pseudomonas aeruginosa is a most opportunistic pathogen – a Gramnegative, rod bacterium that causes infections in both immunocompromised and immunocompetent humans.8 This bacterium is typically found in the environment, and in particular in the soil and freshwater. It is this bacterium’s love for aquatic environments that results in it being present in sinks, showers, swimming pools, hospital reservoirs, ice machines, disinfecting solutions, endoscopes, catheters, and surgical instruments.8
P. aeruginosa can survive on abiotic and biotic surfaces, and can easily be transmitted from one patient to the next.8 The bacterium also possesses many unfavourable characteristics towards its host, which makes it highly resistant to antibiotics, and has the ability to form a biofilm.
Other more common waterborne pathogens are Enterovirus, adenovirus, Pseudomonas spp., legionella, salmonella, and Escherichia coli O157:H7. Outbreaks of these viruses and bacteria are harmful to our healthcare system, as they can be easily transmitted, can be resistant to chemical/ heat disinfection, and possess antibiotic resistance.
Biofilm formation
Unfortunately, microorganisms are extremely clever species, which makes it more difficult for the human eye to detect them. Some microorganisms have the ability to manipulate their morphology as an adaptation and survival method. This method is commonly known as biofilm formation. This a key characteristic for many microorganisms, as it allows them to survive and replicate when conditions become unfavourable for them to sustain life. Biofilms allow some microorganisms (single celled) to survive, as they incorporate them into the ‘group’, so that they, along with multicellular bacteria, fungi, viruses, and protozoa, can continue to replicate and grow.9
In order for microorganisms to create a biofilm, they alter the regulatory networks that are responsible for signal generation.9
This altered signal generation is then used for gene alteration, which results in temporary reconfiguration of the cell.9 These modified genes are responsible for nutrient usage, virulence factors, and the ability to use different surface molecules.8,9 This causes the formation of a biofilm. In this biofilm, the bacteria are wrapped up in a self-produced extracellular polymeric substance (EPS), carbohydrate binding proteins, Pilli and flagella, that allow the bacteria to stick to surfaces.8,9 This EPS layer acts as a shield, that protects the microorganism from unfavourable environmental conditions such as heat and chemicals.
Resistant and hard to eliminate
The longer that a biofilm is attached to a surface such as pipework, the stronger and more resilient it becomes, thus making it extremely hard to break down and eliminate. There are two main common causes of biofilm formation: 1) deadlegs – sections of pipework the water does not cover when flowing through the pipe and, 2) poor water quality. As water is a ‘naturally made’ product, its prototype can vary from one droplet to the next. This makes water particles very unpredictable, which has a significant effect on how water is used throughout healthcare.
Biofilm case study
As previously mentioned, the formation of a biofilm is not always visible to the human eye. Normally a biofilm only becomes visible when it’s too late. This is why medical equipment through which water flows is designed to ensure that there are minimal, or indeed no deadlegs present, reducing the opportunity for these microorganisms to form a biofilm.
That said, a few years ago, an Irish hospital had a confirmed outbreak of Pseudomonas aeruginosa in its water samples, taken as part of its regular validations in the Decontamination Department. The machine in question was taken out of use, and an investigation carried out. The first step was to re-sample to ensure that it was not a ‘false positive’ result. The results from the re-test showed Pseudomonas aeruginosa was present. The manufacturers of the Department’s washer-disinfectors and reverse osmosis units were called in to complete various disinfection activities and troubleshooting to identify the possible source of the contaminant. However, nothing was found in either the water supply or the washerdisinfectors. There were also no deadlegs found
It was only on further investigation of the Decontamination Department that it was concluded that the PTFE tubing routinely used to take its water samples contained a biofilm. The majority of personnel wouldn’t know what a biofilm looks like, but in this case, the representative from one of the manufacturing companies knew what to look out for. Once it was discovered, the presumptive cause of the contamination was investigated, and it was confirmed by microscopy and laboratory analysis. The growth of this biofilm was as a result of the tubing remaining moist, and it being stored in optimal conditions in between the weekly water sampling. Luckily for the hospital, all that was required was to replace the tubing, and the contamination was eliminated.
Water treatment options
As water is one of the main avenues of transmission of pathogenic bacteria in hospitals, a range of different water treatment systems have been developed, installed, and maintained, throughout hospitals to reduce the spread of them. Some of these water treatment systems included copper/silver ionisation, chlorine dosing, ion-exchange (water softeners), washer-disinfectors and reverse osmosis systems. A lot of these water treatments are used together to ensure that the risk of causing infection to the patient is significantly reduced, or even better, eliminated. Innovative technologies for water treatment are continuously being developed and improved to help reduce the number of HCAIs, and continue to target not only pathogenic microorganisms, but also various other pollutants.
Pre-treatment
A key element of the water treatment process is the use of pre-treatment to remove as many chemical ions as possible from the water before it feeds into the reverse osmosis unit. Pre-treatment – which is responsible for the removal of calcium ions, iron, manganese, silica, and carbon dioxide – addresses either the hospital’s ‘raw’ water supply, or partially treated water. Depending on the site’s location, the mains water could be classified as ‘hard’ water, simply signifying that the water supply contains an abundant amount of chlorine and magnesium ions, which, when allowed to build up, or when heated, can cause a build-up of limescale in pipework, resulting in damage to the system it is feeding. Hard water is very easily treated through pre-treatment and other water treatment technologies such as reverse osmosis
There are numerous types of pretreatments available, depending on the desired quality of water required for use. Each pre-treatment is responsible for removing different chemical ions from the water supply, which is why, more often than not, pre-treatment technologies are combined. The most common forms of pre-treatment used in healthcare are sand filtration, carbon filtration, ion exchange (softeners), and organic scavengers. Pre-treatment is not only used to treat the water, but also designed to protect the system, which in return results in an increase in the longevity of the system and its components.
Carbon
Carbon is one of the most used pre-treatments, as it removes impurities in terms of both chemical and microbiological sediments. This process occurs through absorption, in which the contaminants are trapped inside a carbon particle that can be described as being like a pore.11 While different types of carbon can be used, granular activated carbon (GAC) is used most frequently, as it has a larger pore surface, and can thus absorb more compared with other types.11 The carbon acts as a catalyst, as it is used to trap the water contaminants. However, it does not trap salts, other important minerals, and some microorganisms. Carbon is frequently used to remove organic ions from a water system.
Ion exchange
Softener resin is used to break down the chlorine and magnesium ions that cause the raw water to be classified as ‘hard’ water. The resin in the softening vessel can be thought of as meniscal beads. Each of these beads is charged with a sodium ion (negatively charge), so that as the hard water enters the vessel, the ions are attracted to the beads, which causes a sodium ion to be released into the freeflowing water. Other positively charged ions (cation), such as iron, also bind to the resin beads (Figure 4).
Reverse osmosis
Reverse osmosis is the most generic form of water treatment available today. This valuable technology is widely used across not only the healthcare sector, but in many other industries too. So, what is so special about this technology compared with those we have already focused on? Reverse osmosis systems are designed for the degradation of microorganisms. Osmosis is the scientific term given to the natural movement of water molecules from an area of low concentration to an area of high concentration, across a semi-permeable membrane. A semipermeable membrane allows for certain molecules to pass through, while blocking larger molecules from penetrating the membrane. Reverse osmosis sees this process switched – through the addition of pressure via a pump, which results in a high quantity of particles such as salt, chemical ions, and microorganisms, getting trapped in the membrane (Figure 5).13 The most widely used membrane for reverse osmosis is made from a compound called a polyamide. Polyamide membranes are the preferred material used in membrane production. They can be used in a diverse range of applications, as they have more flexibility, and require less pressure, as well as a low flow rate, to achieve high rejection of contaminants including microorganisms.
Conclusion
There is no doubt that, due to the intelligence of microorganisms, combating healthcare-associated infections will be an ongoing battle for the healthcare sector. That said, however, through continuous improvements in water treatment technology, we are now getting more efficient in helping to reduce the rate of contamination. With this, and a growing understanding of how different microorganisms use their hosts and cause infection, we can strive to bring down the number of HCAIs. Frequent water testing in hospitals can ensure quality assurance that the water systems our hospitals have in place are working correctly, which adds to the reassurance that the correct steps are being taken to uphold patient safety.
Michelle Roe
Michelle Roe studied Microbiology at University College Dublin, subsequently working in an environmental microbiology laboratory in the city for almost five years, where she progressed through a number of roles. In her current role at Whitewater, she sells water treatment systems for hospitals across both the UK and Ireland.
References
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12 Herco Wassenentecknic pre-treatment presentation/
13 www.aquacure.co.uk