1. Water hygiene and safety
53
Health Estate Journal
January 2016
P
ublished in 2013, Pseudomonas
aeruginosa – advice for augmented
care units, the new Addendum to
Health Memorandum 04-01 on the control
of Legionella in water, blazed a trail in
changing the perception of the role of
water in transmitting hospital-acquired
P. aeruginosa and other waterborne
bacterial infections to vulnerable healthcare
patients. Reports of the association
between water and Pseudomonas
infections have been accumulating over
many years, some going back as far as
the 1980s, but the high profile deaths
in 2011/12 of four babies in Northern
Ireland’s neonatal units from P. aeruginosa
infections very firmly established the link
between water and Pseudomonas
infections when the source of the outbreak
was traced back to contaminated water
and biofilm in taps. Directly stimulated
by this tragedy, HTM 04-01 has been
a landmark, the first guidance to be written
for P. aeruginosa based on the formation
of multidisciplinary Water Safety Groups
(WSGs) and detailed Water Safety Plans
(WSPs).
However, as the Addendum itself
acknowledges, any guidance is only as
good as the knowledge on which it is
based: “The current state of knowledge
on P. aeruginosa, taps, and water systems,
is not extensive, and is based on limited
scientific evidence. This guidance is
based on current expert opinion and will
develop as the knowledge base expands.”
What new information
has emerged?
So two years on, what new scientific
information on Pseudomonas has
emerged? Has anything come to light
that suggests the Addendum needs
The organism occurs in the environment
in moist habitats, and forms a ‘biofilm’ that
attaches to inanimate surfaces, such as
moist surfaces surrounding handwash
basins. Like Legionella biofilms, the growth
of Pseudomonas in biofilm is encouraged
by conditions such as stagnant water in
system deadlegs, and non-metallic
materials such as EPDM used in solenoids
and flexible hoses. P. aeruginosa is also
found in limescale deposits and trapped
debris, particularly in tap fixtures such as
tap outlets, flow straighteners, and aerators.
In the clinical environment, P. aeruginosa
particularly favours the plastic materials
found in prosthetics such as urinary tract
catheters and respiratory tract tubes in
ventilated patients, and also grows on
moist wound surfaces such as burns
wounds and diabetic ulcers. P. aeruginosa
is the cause of up to 25% of all ventilator-
associated pneumonias (VAP), which
account for around 50% of infections
acquired on intensive care units (ITUs).
Around 20% of all ventilated patients are
at risk of VAP, which is responsible for
up to 40% of deaths in these patients.
P. aeruginosa has become highly resistant
to many antibiotics, constantly increasing
the dangers to those affected.1,2
Person-to-person transmission
Dr Robin Smith, a consultant
microbiologist and infection control doctor
at the Royal Free Hospital in London,
emphasised that traditionally, person-to-
person transmission of P. aeruginosa
infections has been considered inevitable
in healthcare settings, although
evidence of the involvement of water
in transmission has been increasing
rapidly. In another presentation, Dr Beryl
Oppenheim, consultant microbiologist and
Pseudomonas – current
and emerging issues
Susan Pearson* reports on some of the most interesting presentations at an International Biodeterioration and
Biodegradation Society (IBBS) and Public Health England conference on ‘Water microbiology – current and emerging
issues in healthcare’, held at the University of Winchester in early September.** Two and a half years after the
publication of the Addendum to HTM 04-01 – which gave advice on controlling and minimising the risk of morbidity
and mortality due to P. aeruginosa in augmented care units – a major focus at the event was on how well the Addendum
had been working for those ‘at the frontline of infection control’, and what improvements, if any, might be needed.
adjustment? How well has the Addendum
been working for those in the infection
control frontline? Have any pitfalls
emerged, and what improvements,
if any, might be needed?
These were some of the issues recently
under discussion in a session focusing
on Pseudomonas aeruginosa at the
International Biodeterioration and
Biodegradation Society (IBBS) and Public
Health England conference on ‘Water
microbiology – current and emerging
issues in healthcare’ in Winchester in
early September 2015. The presentations
examined the role of Water Safety Groups
in minimising risks to patients, and
looked at new data on the role of water
in the transmission of Pseudomonas
aeruginosa infections.
The ‘essentials’ of P. aeruginosa
The essentials of P. aeruginosa have been
described several times before in Health
Estate Journal. To give a quick re-cap – this
is a bacterium that can occur naturally in
healthy individuals without causing
problems, but can become significantly
pathogenic in immunocompromised
individuals, in which it can cause severe
infections. P. aeruginosa has now become
a common healthcare infection, prevalent
in augmented care units.
CreativeCommonslicence.

2. Water hygiene and safety
54
Health Estate Journal
January 2016
joint theme lead, of the Surgical
Reconstruction and Microbiology
Research Centre, University Hospitals
Birmingham NHS Foundation Trust,
reminded the audience that, unlike in
adults, Pseudomonas does not occur
naturally in neonates: the occurrence
of P. aeruginosa means “you know you
have a problem [because] it is clearly not...
part of their normal flora,” she said. “If a
neonate acquires Pseudomonas, you know
it’s new. This is completely different from
adult patients, who have been through
lots of different wards and treatments.”
Addendum guidance
Dr Jimmy Walker of Public Health
England’s (PHE) Biosafety Group at Porton
Down, one of the conference organisers,
described how his team had
a major part in tracking down the role
played by water as a vector in the
transmission of P. aeruginosa in the
Northern Irish outbreak. This in turn
led to the Porton group’s involvement
in helping to put together the new
national guidelines.
Working closely with the affected
neonatal units, the researchers
dismantled and analysed taps and outlet
fittings. Out of approximately 500
components from five taps, they found
that 14% were positive for the same strain
of P. aeruginosa as that isolated from
the affected patients. P. aeruginosa was
located within two metres of the water
outlet, and sensor taps, which contain
numerous highly engineered components,
were found to be significantly more
colonised than non-sensor taps. In some
cases levels as high as 2.2 x 107 CFU
(colony forming units: each colony
equivalent to one organism) of
P. aeruginosa were found in the biofilm,
which sloughs off into water when taps
are run for handwashing.3
Contaminated equipment
Dr Walker also described how a recent
study found that in hospital environments,
over 50% of the equipment sampled was
highly contaminated with P. aeruginosa,
with the organism repeatedly isolated from
sinks, sensor taps biofilm, showers, and
bedside tables. The contamination was
found to be related to the surface
humidity, and tap water (biofilm).4
So, what is the Addendum’s remit?
The guidance is highly focused on the
development of local Water Safety Groups
and Plans. It outlines how to assess the
risk to patients if water systems become
contaminated with P. aeruginosa or other
opportunistic pathogens, instructs on
what actions to take if water systems do
become contaminated, and provides
protocols for sampling, testing, and
monitoring water for P. aeruginosa.
The details of what Water Safety
Groups need to achieve were outlined
by Dr Smith, who explained that a WSG
is a multi-disciplinary group formed to
undertake the commissioning and
development of a Water Safety Plan. The
Group advises on remedial actions when
contaminated water outlets are found, and
looks at risk to susceptible patients. The
Group comprises a wide range of different
professionals: the infection control team,
consultant microbiologist (often one and
same thing), the estates team, the
facilities team, e.g. cleaning staff and,
in Dr Smith’s hospital, risk and safety
representatives and the project
department, which looks after new-builds
or big changes to buildings’ structure.
The remits of the WSG and Water Safety
Plan are outlined in Figures 1 and 2.
Challenges to compliance
The Addendum is ‘a brilliant document’,
Dr Smith emphasised, but stressed that
there were significant day-to-day
challenges in following it, and that it can
be ‘very difficult to comply with’. She gave
some examples:
Sampling
A lack of clarity over the Addendum’s
definition of ‘augmented care’ has led to
the decision to test water in several day
care units, as well as 16 out of the Royal
Free’s 28 wards. This means a huge
amount of testing: over 600 water outlets
are tested routinely every three months,
with re-testing for positive outlets and
outlets undergoing remedial work.
Sensor taps
These were found to be problematic,
as they do not always flush for very long,
although some can be programmed to
flush for longer. Internal solenoids were
also found to become colonised with
Pseudomonas. A decision was taken
to remove all infra-red taps.
Sinks
Dr Smith noted that some haematology
patients may have as many as four water
outlets in their vicinity, which can lead
to many sinks becoming stagnant from
under-use. Outlets in rooms that are no
longer in regular use – perhaps they have
become storage areas – may also lead
to water stagnation within a system.
Staff shortages
This is one of the bigger problems,
Dr Smith said, and has often been
headline news over the past 18 months.
For example, some London Trusts are
running on a 40% shortage in nursing
staff. She said: “What this means is that
nurses don’t have time to attend Water
Safety Groups, appropriate clinical practice
suffers – as water is very low down the
priority list, and training also suffers.”
Dr Smith gave some examples where
overstretched staffing levels had led to the
disposal of patient material (e.g. patient
wash water) in handwash basins, leading
to environmental contamination. She
stressed: “Getting the message from the
WSG out to the thousands of other staff in
a hospital can be very difficult... education
and more education is really important.”
Patient behaviour
Patients have very occasionally been
found to have removed POU filters from
showers to improve water flow. POU filters
are fitted to deliver P. aeruginosa-free water
or prevent the dissemination of Legionella
via aerosols – unfortunately their removal
negates the control of these opportunistic
pathogens.
Persistent contamination
Outlets found to be persistently positive
for Pseudomonas are on the increase,
Fig. 1: Water Safety Group remit
ᔢ Identification of hazards.
ᔢ Assessment of risk.
ᔢ Identification and monitoring of control methods.
ᔢ Development of incident protocols.
ᔢ Development and delivery of the WSP.
ᔢ Training.
ᔢ Demonstration of governance and assurance to the Trust board.
Fig. 2: Water Safety Plan
ᔢ Assist with understanding and mitigating contamination risks from water
distribution and supply systems and all associated equipment.
ᔢ Provide a risk management approach to the microbiological safety of water.
ᔢ Establish good practices in local water usage, distribution, and supply.
PortonDownBiosafetyGroup,PHE
An outlet fitting after four months of use.

3. Water hygiene and safety
55
Health Estate Journal
January 2016
Fig. 4: Control measures outlined in the
HTM 04-01 Addendum guidance
ᔢ Estates
Similar to Legionella – ‘Keep it moving’.
Review outlet design, eliminate
plastics/nooks and crannies.
Regular maintenance, de-scaling etc.
Regular testing.
Remedial work.
Stay on top of new-
builds/modifications.
Temporary point-of-use filters until
remedial action effective.
ᔢ Facilities
ᔢ Cleaning of outlets.
ᔢ Clinical staff
Keep water moving.
ᔢ Flushing of infrequently used outlets.
ᔢ Reporting faults.
Appropriate clinical practice.
ᔢ Education
Dr Smith said, adding: “This has been
happening even after we’ve changed
sinks and taps.”
Dr Smith concluded that ‘although the
Addendum is helpful and comprehensive
– it tells you exactly what you should do –
the reality is much more challenging’.
To follow the guidelines ‘requires lots of
money, time and staff engagement – three
things that are getting tighter every day’.
Dr Oppenheim also stressed that the
Addendum ‘is a very clear and an
excellent document’, but ‘is difficult to
do in real life’. She said: “The really
difficult part of it is knowing how to do
the surveillance on patients when you’re
talking about adults in augmented care.
What constitutes a new case? How do
you count it? How do you say where that
person might have acquired it?”
New data
Dr Walker stressed that understanding
of the science on which the current
guidance is based is ‘continually moving
on as new information emerges’.
Flushing and flow straighteners
At Porton Down, data from a test rig
incorporating 27 taps of the type used in
the Northern Irish neonatal units has
demonstrated – from analysis of
numerous outlet components – that the
outlets themselves may not always be the
source of Pseudomonas contamination
in handwash basins.
Each tap in the test rig comprised the
outlet itself and an associated solenoid
valve and TMV. Following inoculation
of the rig with P. aeruginosa, many
months of water sampling established
that the majority of the outlets became
contaminated. However, after one year,
no Pseudomonas was recovered from the
outlet components – despite the presence
of scale deposits on the components.
Biofilm build-up
Instead, analysis of components beyond
the outlets themselves revealed extensive
build-up of biofilm on the EPDM material
inside the solenoid valves. Solenoid valves
have been found to be culprits for biofilm
growth before, but, Dr Walker said, they
discovered that when new solenoids were
put in place, they did not become colonised
– and removal of flow straighteners made
no impact on those results.
Dr Walker reminded the audience that
flushing and keeping hot water hot and
cold water cold are considered major
strategies in controlling bacterial
contamination of water. The outlets on
the test rig were split into two groups:
one group was flushed twice a day, while
the others were flushed five times a day.
However the more frequently flushed
outlets did not show any reduction in
microbial content of the water samples.
Importantly, when the regular twice
or five-a-day flushing was stopped, and
the outlets were sampled once a week,
over several weeks, microbial content,
including P. aeruginosa, did increase.
The Group concluded, Dr Walker said,
that ‘flushing does have a role to play in
reducing proliferation of the microbial
consortia including the opportunistic
pathogens, but will not remove
contamination. If you stop that flushing,
you get an increase [in microbial
contamination] – but flushing does not
control [contamination] as such’. (Figure 3.)
Links with water: non-outbreak study
Much of the literature implicating water
as a vehicle for transmitting Pseudomonas
infections has been published in relation
to defined outbreaks. Dr Oppenheim
discussed the findings from an important
new study that asked the question:
‘Is water really an important source
of acquisition of P. aeruginosa in adults
in a non-outbreak setting?’
The study, carried out at the University
Hospitals Birmingham (UHB) NHS
Foundation Trust, which is a major burns
centre, focused on patients with severe
burns. P. aeruginosa is a major pathogen
in these patients, causing colonisation,
extensive damage to grafts, and systemic
sepsis. Water plays a critical part in burns
treatment, in first aid immediately after
a burn, and in hydrotherapy is used to
clear build-up of detritus on the surface
of wounds – and reports of links between
water and P. aeruginosa infections in burns
patients go as far back as the 1990s.
Patients on the UHB burns unit are
showered on a dedicated trolley within
cubicles specifically designed so that
they can receive hydrotherapy within
their own room. An initial audit found
around 30% of large burns patients
developed P. aeruginosa colonisation.
Dr Oppenheim’s research team focused
on investigating the use of next generation
whole genome sequencing to acquire the
fine detail needed to work out if bacterial
strains from different samples are really
linked to each other. She noted that
bacteria can also be sequenced using
multi-locus sequencing typing, which
sequences only a few specific genome loci
to generate a pattern. In some Legionella
outbreaks, use of this method has clearly
linked patients and water samples because
the strains involved were very rare.
Whole genome sequencing
Pseudomonas sequence types found in
water in healthcare environments are very
widespread internationally, “so if you have
a patient with the same sequence type as
the water it doesn’t necessarily mean very
much,” Dr Oppenheim said. The group
decided to use whole genome sequencing,
which meant they could examine every
nucleotide in a bacterial genome and
note any differences – known as single
nucleotide polymorphisms – between
strains. “This enhanced resolution gave us
really forensic details about the bacteria,
for example linking a strain to antibiotic
resistance.” The team used the Illumina
MiSeq system, which provided relatively
low cost results comparable with many
other typing systems. Dr Oppenheim
emphasised her belief that this type of
analysis, as it goes on dropping in cost,
represents the future for microbiology.
The group took wound, stool, and urine
samples from their burns patients on
admission, as well as environmental
samples from their rooms. As soon as
a patient was identified as Pseudomonas-
positive they were recruited onto the main
study. Wound swabs were taken at every
dressing change, lots of environmental
sampling was carried out, and many
bacterial strains were saved for sequencing.
Dry vs. wet sites
Results from the environmental sampling
were much as expected: the dry sites
(chairs, tables etc.) were negative for
Fig. 3: Conclusions from Porton
Down test rig
1. The flow straighteners/aerators
did not become contaminated
with P. aeruginosa.
2. The solenoid valve did become
colonised. Removing or replacing
this component reduced the level of
P. aeruginosa in the tap water to below
the detectable limit (< 1 cfu/100 ml).
3. The solenoid valve represents
a weakness within the system –
alternative materials need to be
investigated.
4. Flushing does appear to have a role
to play, but can be a waste of water.
Flushing can reduce the proliferation
of the microbial consortia, but will
not remove contamination.

4. Water hygiene and safety
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Health Estate Journal
January 2016
Pseudomonas, while half of all the wet
sites (taps, showers etc.) were positive.
Given the initial 30% figure, the
researchers expected to identify at least
10 colonised patients during the study;
however only five were identified. The
study started during a period where
interim guidance had been released
prior to the publication of the Addendum,
so the low number could be due to
intensified infection control measures,
for example increased flushing of water
outlets and increased cleaning.
One patient arrived on the unit already
carrying P. aeruginosa, one patient was
found to have a completely unique strain,
and another acquired P. aeruginosa from
the ITU. “But what was interesting,”
Dr Oppenheim commented, “was that
most of these infections derived from
water, and Pseudomonas in two of these
patients came from the same multi-locus
type, ST395.”
Correlating these results with a plan
of the burns unit, the researchers found
that the all the positive sample strains
from environmental wet sites were mostly
very closely related. However, what was
really significant was that the wound
swabs from the two patients who had
acquired identical strains were also
identical to the both the water and
environmental isolates from one room –
in which they had both been treated.
A ‘smoking gun for sequencing’
Dr Oppenheim told the audience: “We think
this really is a smoking gun for sequencing,
telling us that there is definitely a
transmission – but you could always ask
which direction it’s going in – from the
patient to the water, or from the water and
back again? But these patients inhabited
this room consecutively, so even if one
[patient] contaminated the water supply –
which doesn’t seem likely given that the
whole water supply in the unit is very
similar – the second one couldn’t. From
this we can conclude that Pseudomonas
went from the water to the patient.”
Dr Oppenheim also emphasised
that this one sequence type is found
throughout the burns unit, yet the unit
was commissioned only five years ago.
She said that the most likely explanation
might be that the outlet components could
have arrived pre-seeded with the strain.
Another important piece of information
came out of this research: all of the
patients on the unit were showered daily for
weeks, and most did not become infected
with Pseudomonas. “We don’t know what
is special about the people who did
develop infections,” Dr Oppenheim said.
“While the majority of patients admitted
to the burns unit do not carry detectable
levels of P. aeruginosa, contaminated
water does play a role in the transmission
of Pseudomonas on a burns unit, but
it is not the only source. However, these
are specialised patients who are highly
exposed to water; can we make any leap
to say water is also an important source
in other patients?”
“For the moment we don’t have
a final engineering solution,” she said.
“We currently have POU filters on the
highest risk water outlets in that unit.”
Drains
There are increasing reports of incidents
involving drains in transmitting
Pseudomonas infections, suggesting
that water outlets are just the tip of the
iceberg. Dr Walker gave examples from
several papers from The Journal of
Hospital Infection.
A 2013 report details how water from
a tap that was directed straight into the
outlet, allowing splash-back from the sink
drain trap, was implicated in 103 cases
(76.3%), while visible splashing out of
and close around the sink when the tap
was turned on was recorded in 34 cases
(25.2%).5
A 2012 paper, meanwhile,
describes how bacteria from a heavily
contaminated plughole were probably
splashed around and heavily aerosolised
when the tap was run,6
while in a 2014
Scanning electron microscopy of biofilm.PortonDownBiosafetyGroup,PHE
Fluorescent labelled P. aeruginosa
biofilm on a glass surface x1000.
DrJ.Webb,UniversityofSouthampton
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5. Water hygiene and safety
57
Health Estate Journal
January 2016
paper, transmission from sinks to patients
was stopped by integrating self-disinfecting
siphons to all sinks on an ITU.7
Dr Smith described an incident at the
Royal Free ITU. An elderly patient who had
previously been healthy, so had not been
subject to many healthcare interventions,
and who had not travelled abroad, became
infected with a very rare ‘highly drug-
resistant Pseudomonas strain associated
with foreign travel. This was such an
unusual strain that the unit could identify
only one other patient who had also been
colonised. When the team investigated,
they discovered that this patient had been
transferred from Nigeria; however, this had
been nearly two years previously. The only
connection between the patients was that
they had occupied the same room. Swabs
of the handwash basin drains revealed the
culprit, which, for some reason, had been
quiescent in the period between the two
infections.
Conclusions
Both Dr Smith and Dr Walker reminded
the audience of the control methods
outlined in the Addendum for controlling
bacteria in water, summarised in Figure 4.
Dr Walker emphasised that much of
control comes down to identifying
deadlegs (sources of water stagnation),
and reviewing plumbing. Along with the
examples at the Royal Free and UHB
described above, there are many
examples of outlets remaining positive
despite extensive remedial action. Flow
straighteners are not always the cause
of contamination, and extensive flushing
is not always the solution. Dr Walker also
noted there have been situations where
bacteria have been detected in areas of
thermal flushing.
He says: “We know that 10-25% of all
ITU outlets can be positive... at the end
of the day there are weak points in water
systems – we need to work out why some
control methods are not working, and
work out and investigate other control
strategies. Is what is happening
connected with antibiotic-resistant
strains? The involvement with drains?
I think the control of P. aeruginosa requires
the Water Safety Group to take a... really
forensic approach to working out what
control methods will be effective.” ✚
The Department of Health will be reviewing
the content of HTM 04-01 in due course
to align it with the HSE Approved Code
of Practice for the Control of Legionella
in Water Systems.
The author acknowledges the help
and input of Pall Medical in the
preparation of this report.
References
1 Vincent J-L et al. The Prevalence of
Nosocomial Infection in Intensive Care
Units in Europe. Results of the European
Prevalence of Infection in Intensive Care.
(EPIC) Study. EPIC International Advisory
Committee. JAMA 1995; 274 (8): 639-644.
2 Melsen W et al. Estimating the attributable
mortality of ventilator-associated
pneumonia from randomized prevention
studies. Crit Care Med 2011; 39: 1-7.
3 Walker J. et al. Investigation of
healthcare-acquired infections associated
with Pseudomonas aeruginosa biofilms
in taps in neonatal units in Northern
Ireland. J Hosp Infect 2014; 86: 16-23.
4 de Abreu PM et al. Persistence of
microbial communities including
Pseudomonas aeruginosa in a hospital
environment: a potential health hazard.
BMC Microbiol 2014; 14: 118.
5 Roux D et al. Contaminated sinks in
intensive care units: an underestimated
source of extended-spectrum beta-
lactamase-producing Enterobacteriaceae
in the patient environment
J Hosp Infect 2013; 85: 106.
6 Starlander G et al. Minor outbreak
of extended-spectrum lactamase-
producing Klebsiella pneumoniae
in an intensive care unit due to
a contaminated sink. J Hosp Infect
2012; 82: 122.
7 Wolf I et al. The sink as a correctable
source of extended-spectrum-lactamase
contamination for patients in the intensive
care unit. J Hosp Infect 2014; 87: 126.
* Susan Pearson BSc is a freelance
journalist and communications
consultant specialising in medicine
and the environment.
** ‘Water microbiology – current and
emerging issues in healthcare’ was
held from 7-8 September, 2015 at the
University of Winchester. Another water
microbiology workshop will be held
during the next IBBS Triennial conference
in Manchester in 2017. For further
information, visit: www.ibbsonline.org
Ability of Pseudomonas to adapt within biofilm
may encourage pathogen evolution
Biofilms can be very tolerant of a broad
range of microbial treatments. Whether
these are biocides such as chlorine in
water, or antibiotics in clinical infections,
there will always be sub-populations
of cells that survive treatment due
to their location and inaccessibility
of the disinfectants, and, as
a consequence, persist to re-seed
water or cause further infections.
At the University of Southampton,
research has focused on investigating
the genetics of Pseudomonas in relation
to the physiology of biofilm to see if
there is scope for controlling biofilm by
interfering with its formation and survival.
According to Professor of Microbiology,
Dr Jeremy Webb, bacterial species
within a biofilm diversify very quickly
into a whole range of different colony
phenotypes within a matter of days. There
appears to be a lot of genetic variation
occurring in biofilms: the outward
appearance of colonies changes, but
Pseudomonas clones can also lose the
ability to grow on some substrates,
and gain the ability to utilise others.
Using fluorescence to measure
mutations in real-time, the research team
has established that Pseudomonas bacteria
within biofilms often reveal a high frequency
of mutation – it is also known that a high
proportion of antibiotic-resistant strains
isolated from biofilm also demonstrate
a high frequency of mutation (a ‘mutator’
phenotype). So what is the importance
of mutation frequency and diversification,
and the ability of Pseudomonas to colonise
and survive in water systems?
A laboratory set-up
Using a laboratory set-up to provide a
continuous flow of tap water through a
flow cell system and into a waste reservoir,
the group has been studying the biofilms
that form in channels within flow cells.
These have been pre-colonised with
communities of drinking water bacteria,
and a range of fluorescent-tagged
Pseudomonas strains added to study
the integration of these strains into the
drinking water biofilm community.
The strains used were a wild type
Pseudomonas strain and mutS strains.
The mutS strains are deficient in their
ability to repair errors and mutations,
as they occur in their DNA, and have
a much higher frequency of mutation
than the conventional wild type strain.
The fluorescent mutS strain displayed
a significant ability to integrate and
colonise within the drinking water
biofilm. The high frequency mutation
strain is able to colonise better into a
drinking water biofilm than the wild type.
This suggests that diversification/
mutation frequency does play a role in
the ability of Pseudomonas to colonise
and survive in biofilms, and that mixed-
species biofilms may play an important
role as foci for genetic adaptation and
evolution of microbial pathogens.