The Science Behind BioShield
Let’s consider the issue of microbiological
contamination of groundwater wells, which impacts
affordability, source sustainability and public health.
According to the USGS, groundwater sources supply
approximately 20% or 84.6 billion gallons per day of
fresh water used in the United States.
These precious
groundwater
resources must
be managed and
protected by
implementing
strategies to
ensure
groundwater
quantity, such as
well yields, and
groundwater
quality with
respect to
bacteriological
impacts.
Is groundwater a sustainable resource?
The number one reason for loss of
production and abandonment of ground
water wells is Biofouling. The number
one agent of biofouling is iron related
bacteria.
Biofouling or biological fouling is the undesirable
accumulation of microorganisms on submerged
structures.
Individually small, accumulated biofoulers can form
enormous masses.
Biofouling can occur in groundwater wells where
buildup can limit recovery flow rates and clog pumps
and piping.
A variety of bacteria are indigenous to soils and
groundwater. These are mineral utilizing species of
bacteria which exist in low numbers in groundwater as
this is a low nutrient environment.
Bacteria in nature are most frequently encountered not as
free-swimming organisms but as surface-attached
communities known as biofilms.7
Organisms residing within biofilm possess a number of
advantages over their free-swimming or planktonic
counterparts, including increased resistance to adverse
environmental conditions and antibacterial agents.
The ubiquity of biofilm development can cause
significant problems in the areas of
public health, 8, 9
medicine, 10, 11, 12
and industry. 13, 14
Accordingly, there has been a great deal of research to
better understand biofilm development and to identify
improved strategies for biofouling control.
Earth’s Composition
5% Earth’s crust is
Iron
Almost every
groundwater
source contains
measurable
amounts of Iron
“Surface waters contain an innumerable variety of organics
from municipal or industrial wastewater effluents, storm
water runoff, agricultural activities and natural vegetation,
producing humic substances. Total organic concentrations
range from 1 to 10 mg/L at the water supply intake with 7
mg/L on average.”1
“For aquatic systems the organic matter includes dissolved
organic carbon (DOC) and particulate organic carbon.
Groundwater systems are frequently among the most
oligotrophic microbial environments that have ever been
described (mean concentration from 0.1 to 0.7 mg/L).”2
However, where one measures high organic carbon in the
subsurface water, this difference is attributable to microbial
activities. Bacterial carbon production rates are extremely
high in biofilm communities.3
However, when these bacteria enter groundwater wells,
they become attached to surfaces within the well,
particularly areas of high velocity, and they begin to
dramatically increase in number.
National Secondary Drinking Water
Regulations
Contaminant
National Secondary Drinking Water
Regulations (NSDWRs or
secondary standards) are nonenforceable guidelines regulating
contaminants that may cause
cosmetic effects (such as skin or
tooth discoloration) or aesthetic
effects (such as taste, odor, or
color) in drinking water. EPA
recommends secondary standards
to water systems but does not
require systems to comply.
However, states may choose to
adopt them as enforceable
standards.
Aluminum
Chloride
Color
Copper
Corrosivity
0.05 to 0.2 mg/L
250 mg/L
15 (color units)
1.0 mg/L
noncorrosive
Fluoride
2.0 mg/L
Foaming Agents
0.5 mg/L
Iron
0.3 mg/L
Manganese
Odor
pH
0.05 mg/L
3 threshold odor
number
6.5-8.5
Silver
0.10 mg/L
Sulfate
250 mg/L
Total Dissolved
Solids
500 mg/L
Zinc
http://www.epa.gov/safewater/mcl.html#sec
Secondary
Standard
5 mg/L
Impact of Pumping
Biofouling caused by iron related bacteria can
occur at very low levels of iron due to the
impact of pumping in the well proper.
Small Municipal Well
Casing diameter
Pumping
0.1 ppm Iron
0.1 ppm Iron
92
12,265
6"
Well overall depth
196'
Static Water Level
30'
Pump Gallons per Minute
45
24-hour pump cycle
12
Total milligrams Fe per day
Standing
This sessile, or attached, state is highly immune to biocides,
enjoying from 150-3000 fold immunity.
At the same time, this sessile form, which excretes a polymeric
substance as well as insoluble forms of the minerals they utilize
as hydroxides, begins to build up clogging structures within the
well, pump and distribution piping.
The water these wells produce also contains these polymeric
substances (extracellular polysaccharides) and the ferric
hydroxides as well as sulfate compounds which are very
corrosive.
In addition to the obvious problems associated with such
bacteria, the slime they produce will entrain any minerals in the
gravel pack as water moves into the well. This mineral
encrustation can render a well useless in very short order. Are
you keeping pumping records? Have you noted a decline?
Steps in Biofilm Development
The instant a clean pipe is filled with water, a
biofilm begins to form.
http://www.edstrom.com/resources.cfm?doc_id=143
Step 1: Surface conditioning
• The first substances associated with the surface are not bacteria but
trace organics.
• Almost immediately after the clean pipe surface comes into contact
with water, an organic layer deposits on the water/solid interface
(Mittelman 1985). These organics are said to form a "conditioning
layer“ which often serve as a nutrient source for bacteria.
Adsorption of organic
molecules on a clean surface
forms a conditioning film.
(Characklis 1990)
http://www.edstrom.com/resources.cfm?doc_id=143
Step 2: Adhesion of ‘pioneer’ bacteria
• In a pipe of flowing water, some of the planktonic
(free-floating) bacteria will approach the pipe
wall and become entrained within the boundary
layer, where flow velocity falls to zero.
• Cells begin to form structures which may
permanently adhere the cell to the surface.
Transport of bacteria cells to
the conditioned surface.
(Characklis 1990)
http://www.edstrom.com/resources.cfm?doc_id=143
Attachment = Resistance
• The attachment of bacteria to surfaces
increases resistance to biocides including
chlorine from 150 to 3000 fold.
• Other factors (from 2 to 10-fold) include
biofilm age, encapsulation, and growth
conditions.
• Factors are mulitplicative.
LeChevallier, Cawthon, Lee. Factors promoting survival of bacteria in chlorinated water supplies. AWW Service
Co.
Phenotypic plasticity
The ability of bacteria to adapt to
environmental changes is known as
phenotypic plasticity. A good example
of phenotypic plasticity is planktonic
bacteria in groundwater utilizing a
sessile lifestyle in groundwater wells.
Step 3: Extracellular Polysaccharides ‘slime’ formation
• Biofilm bacteria excrete extracellular polysaccharides, or
sticky polymers, which hold the biofilm together and
cement it to the pipe wall.
• These polymer strands, much like the structure of a
spider’s web, trap scarce nutrients and protect bacteria
from biocides.
• This extracellular slime acts as an ion-exchange system
for trapping and concentrating trace nutrients from the
overlying water.
• The slime acts as a protective coating for the attached
cells which mitigates the effects of biocides and other
toxic substances.
http://www.edstrom.com/resources.cfm?doc_id=143
Step 4: Secondary Colonizers
• As well as trapping nutrient molecules, the
slime net also snares other types of
microbial cells.
• These secondary colonizers metabolize
wastes from the primary colonizers as well
as produce their own waste which other
cells then use.
http://www.edstrom.com/resources.cfm?doc_id=143
Step 5: Fully Functioning Biofilm A
cooperative "consortia" of species
• The mature, fully functioning biofilm is like a living tissue on the pipe
surface. It is a complex, metabolically cooperative community made
up of different species each living in a customized microniche.
• Biofilms are even considered to have primitive circulatory systems.
• Different species live in concert helping each other exploit food
supplies and resist antibiotics. Toxic waste produced by one species
is utilized by another. Functioning symbiotically several species of
bacteria, each armed with different enzymes, can break down food
supplies that no single species could digest alone.
• The biofilms are permeated at all levels by a network of channels
through which water, bacterial garbage, nutrients, enzymes,
metabolites and oxygen travel to and fro. Gradients of chemicals
and ions between microzones provide the power to shunt the
substances around the biofilm." (Coghlan 1996)
http://www.edstrom.com/resources.cfm?doc_id=143
Biofilms grow and spread
• A biofilm can spread at its own rate by ordinary cell
division and it will also periodically release new ‘pioneer’
cells to colonize downstream sections of piping.
• According to Mayette (1992), "These later pioneer cells
have a somewhat easier time of it than their upstream
predecessors since the parent film will release wastes
into the stream which may serve as either the initial
organic coating for uncolonized pipe sections down
stream or as nutrient substances for other cell types."
http://www.edstrom.com/resources.cfm?doc_id=143
Biofilm Cross Section
Bacteria and other microorganisms
develop cooperative colonies or
"consortia" within the biofilm.
An anaerobic biofilm may develop
underneath the aerobic layer.
(Borenstein 1994)
Note: Coliforms are facultative;
they can live in anaerobic or
aerobic conditions.
http://www.edstrom.com/resources.cfm?doc_id=143
How fast does biofilm develop?
• According to Mittelman (1985), the development
of a mature biofilm may take several hours to
several weeks, depending on the system.
Pseudomonas aeruginosa is a common
‘pioneer’ bacteria and is often used in biofilm
research. In one experiment (Vanhaecke 1990,
see test summary pg 11), researchers found that
Pseudomonas cells adhere to stainless steel,
even to electropolished surfaces, within 30
seconds of exposure.
Bacteria exploit every environmental
niche on the planet
• Bacteria exist at the top and bottom of every known food chain
• They are found in:
– Pack Ice
– Undersea superheated vents
– Low pH
– High pH
– Freshwater – Saltwater
This attests to their adaptability and broad phenotypic
plasticity.
Think about it! Bacteria can easily
gain entrance to the water well:
Well head
Soil
Grout seal
Rock
Water Table
Groundwater “aquifer”
Many of man’s activities cause bacterial
contamination of ground water !
Landfills, dumps
Industry
Residential
Agriculture
Gas - Oil Wells
Mining
Location of our water well is important
Ground water in its natural state is not
always free from problem causing bacteria
Microphotographs of bacteria that
precipitate iron and manganese
• Gallionella ferruginea
• Leptothrix cholodnii
• Thiobacillus
• Siderococcus
Why be concerned about iron related
bacteria in groundwater wells?
• Biofouling caused by iron related bacteria
destroys groundwater well and
distributions assets.
• Opportunistic and pathogenic bacteria
colonize biofilm.
Distribution Asset Destruction
Pipe wall Biofouling - Example 4 inch pipe
3/16 inch thick = 12% reduced flow area
3/8 inch thick = 36% reduced flow area
9/16 inch thick = 51% reduced flow area
3/4 inch thick = 64% reduced flow area
1 inch thick = 75% reduced flow area
Effects of IRB
Clogged and corroded piping with rusty sludge (ferric
hydroxides)
Increased chances of sulfate reducing bacteria
infestation – MIC (microbe-induced corrosion)
Unpleasant odors and taste
Increased organic content in water favoring the
multiplication of other bacteria
Severe damage to pumping equipment
Seriously impacts water treatment
Reduces distribution efficiency
Severe blockages in gravel pack, well and screens
Chronic bio-fouling caused by
Iron bacteria
Many wells have been abandoned because of biofouling.
Water flow area virtually eliminated
Emerging Microbiological Issues
Iron Related Bacteria
(Iron, Sulfate, Manganese Utilizing Species)
Galionella
Ferruginea
Sphaerotilus
Leptohrix
Can encourage
pathogen growth
E-Coli
Consortia bacteria in a biofilm
•
•
•
•
IRB
SRB
Coliform Bacteria
Opportunistic bacteria
- Pseudomonas aeruginosa
• Pathogenic Bacteria
- H. pylori
List of Contaminants & their MCLs
MCLG1
Contaminant
(mg/L)2
MCL or
TT1
Potential Health Effects from Ingestion of Water
Sources of Contaminant
in Drinking Water
(mg/L)2
Cryptosporidium (pdf file)
zero
TT 3
Gastrointestinal illness (e.g., diarrhea, vomiting, cramps)
Human and fecal animal
waste
Giardia lamblia
zero
TT3
Gastrointestinal illness (e.g., diarrhea, vomiting, cramps)
Human and animal fecal
waste
Heterotrophic plate count
n/a
TT3
HPC has no health effects; it is an analytic method used to
measure the variety of bacteria that are common in water.
The lower the concentration of bacteria in drinking water,
the better maintained the water system is.
HPC measures a range of
bacteria that are naturally
present in the environment
Legionella
zero
TT3
Legionnaire's Disease, a type of pneumonia
Found naturally in water;
multiplies in heating
systems
Total Coliforms (including
fecal coliform and E. Coli)
zero
5.0%4
Not a health threat in itself; it is used to indicate whether
5
other potentially harmful bacteria may be present
Coliforms are naturally
present in the environment;
as well as feces; fecal
coliforms and E. coli only
come from human and
animal fecal waste.
Turbidity
n/a
TT3
Turbidity is a measure of the cloudiness of water. It is
used to indicate water quality and filtration effectiveness
(e.g., whether disease-causing organisms are present).
Higher turbidity levels are often associated with higher
levels of disease-causing microorganisms such as
viruses, parasites and some bacteria. These organisms
can cause symptoms such as nausea, cramps, diarrhea,
and associated headaches.
Soil runoff
Viruses (enteric)
zero
TT3
Gastrointestinal illness (e.g., diarrhea, vomiting, cramps)
Human and animal fecal
waste
Drinking Water Contaminant Candidate List 2
On February 23, 2005, EPA announced the second
Drinking Water Contaminant Candidate List (CCL) and
our efforts to expand and strengthen the underlying CCL
listing process to be used for future CCLs.
Microbial Contaminant Candidates
Adenoviruses
Aeromonas hydrophila
Caliciviruses
Coxsackieviruses
Cyanobacteria (blue-green algae), other freshwater algae, and their toxins
Echoviruses
Helicobacter pylori
Microsporidia (Enterocytozoon & Septata)
Mycobacterium avium intracellulare (MAC)
Pathogenic Bacteria Colonize Biofilms
In Western countries rates of Helicobacter pylori infection are as high
as 60% by age 65. Infection with H. pylori is now recognized as a
causative agent in chronic gastritis, as well as peptic and duodenal
ulcer disease. In addition, infection with this organism is associated
with mucosa-associated lymphoid tissue lymphoma and
adenocarcinoma. Epidemiological data support transmission
through a common source such as water. Recently the USEPA
Office of Groundwater and Drinking Water included H. pylori in
its contaminant candidate list reflecting concerns over possible
waterborne transmission. Studies have shown H. pylori to be
significantly more resistant to chlorine than E. coli. In the natural
environment, H. pylori form a biofilm in 1 to 15 days. Biofilm
bacteria were found to be 150 to 3,000 times more resistant to
hypochlorous acid than similarly treated unattached microbes.
Several researchers have examined the possible role of biofilms in
the proposed waterborne transmission of H. pylori and have
demonstrated that H. pylori are capable of forming biofilms and of
persisting in mixed-species drinking water biofilms. 18
Changes in human demographics
There is an increasing number of “vulnerable
subpopulations” in the United States such as infants,
children, pregnant women, the elderly, and the immunecompromised who are particularly susceptible to
infections resulting from exposure to waterborne
pathogens compared to the general populace.
Immune-compromised:
Cancer, Crohn’s disease, Lupus, HIV, AIDS
Transplant – organ, bone marrow, stem cell
Rheumatoid Arthritis, diabetes
Steroid use, long term anti-acid users >2 weeks
Smokers
Chlorine is not effective
• Studies have shown that despite the
application of continuous disinfection using
chlorine biofilm rapidly develops. Biofilm
can rapidly form in the presence of a 1 to 2
mg/L free chlorine residual.6
• Given that chlorine is ineffective, what
can be done to remediate or eliminate
biofilm and the associated health risks
in groundwater?
Stressing bacteria is not the total
solution
Stressing bacteria with certain biocides and/or
physical treatments such as heat or
mechanical removal is not the total solution.
1.) Bacteria have short life cycles (20
minutes) which promote a high level
of adaptability to environmental
changes.
2.) Microbiological structures within a
biofilm protect bacteria from
environmental fluctuation.
3.) According to Characklis (1990), biofilm
recovers from stressing.
According to Characklis (1990), biofilm recovery may be
due to one or all of the following:
•
The remaining biofilm contains enough viable organisms that there is no lag
phase in regrowth. Thus, biofilm recovery after shock chlorination is faster
than initial accumulation on a clean pipe.
•
The residual biofilm on the surface makes it rougher than clean pipe. The
roughness of the deposit may provide a stickier surface which adsorbs more
microbial cells and other compounds from the water.
•
The chlorine preferentially removes extracellular polymers and not biofilm
cells, thus leaving biofilm cells more exposed to the nutrients when
chlorination ceases.
•
Surviving organisms rapidly create more slime (extracellular polymers) as a
protective response to irritation by chlorine.
•
There is selection for organisms less susceptible to the sanitizing chemical.
This is usually the organisms that produce excessive amounts of slime like
Pseudomonas.
Shock chlorination is not the solution
Shock chlorination is not the solution. Chlorine is a common
disinfectant used in water systems, and is highly toxic to
coliform and similar types of bacteria. IRB and SRB are more
resistant to chlorine’s effects because they occur in thick
layers and are protected by the slime they secrete. A
standard chlorine treatment may kill the bacterial cells in the
surface layer but leave the rest untouched. In the case of
iron bacteria, iron dissolved in the water may absorb
disinfectant before it reaches the bacteria. For all these
reasons, iron and sulfate related bacteria may be able to
survive a chlorine treatment that would kill other types of
bacteria. Treatment levels of 800-1,000 ppm chlorine are
commonly recommended for treatment of iron and sulfate
related bacteria; however, these levels promote the growth of
coliforms. At best, shock chlorination is minimally effective for
a limited period of time.
The solution to biofouling and all of the
problems that are caused by these
nuisance bacteria is twofold:
1. Rehabilitate the well
2. Maintain the well microbiologically by
continuously controlling
the biofilm forming bacteria
Well Rehabilitation
1.
2.
Use a contractor who routinely provides this service,
and get referrals from their customers.
Use a down well camera to determine the condition of
the well prior to and following rehabilitation.
(consider third party verification)
3. Be certain the contractor uses products which are NSF
certified (Standard 60) for this purpose. Certification
can be verified online at www.nsf.org .
Identifying the Problem
Down the
Well
Camera
The
Problem:
Iron
Bacteria
Fouled well screens reduce flow
Screen blocked by
Iron Related
Bacteria
Abandoned: Iron Bacteria
Well Rehabilitation Under Way!
Well Rehabilitation Under Way!
Well Rehabilitation Under Way!
Well Rehabilitation Under Way!
Well Rehabilitation Under Way!
An Asset Has Value!
Well Rehabilitation
An excellent book on well rehabilitation is
Chemical Cleaning, Disinfection & Decontamination of
Water Wells
by Dr. John H. Schnieders, the principal chemist at Water
Systems Engineering (Ottawa Kansas), a laboratory
which specializes in the microbiology and chemistry of
water.
ISBN 0-9726750-0-0
Continuous disinfection of the well
Quorum sensing is essentially how bacteria communicate
with one another and act as groups.
Bacteria “communicate” on the molecular level utilizing
various chemicals.
Bacteria release a small amount of chemicals as they live and
grow.
As they multiply, the concentrations of these various
chemicals increases in proportion to the number of bacteria.
Continuous disinfection of the well
At a critical point, the bacteria sense that there are
significant numbers of them whereby it would be most
advantageous to act as a group as opposed to acting
individually.
At this point, the bacteria “turn off” the planktonic or
unattached portion of their genetic material and “turn on”
the sessile or attached portion of their genetic code.
(phenotypic plasticity)
Continuous disinfection of the well
Quorum sensing allows a single celled organism to
act as a multi-cellular organism.
Bacteria recognize and communicate within their
own species as well as with other species.
The manner in which they communicate within
their own species is different from the manner in
which they communicate with other species.
Continuous disinfection of the well
•Recent biofilm research has focused on the role of
cell-to-cell signaling within biofilm populations.
• Bacteria are able to produce and respond to various
hormone-like signal molecules.15
•A particular subset of these molecules, the acylated
homoserine lactones (acyl HSLs), have been shown to
be involved in biofilm formation and dispersal with
Pseudomonas aeruginosa.16
•This finding suggests that interference with acyl
HSL-based signaling may provide a novel
mechanism for biofilm control.
Continuous disinfection of the well
Studies conducted aver the past 10-15 years
demonstrate that acyl-HSL based signaling
systems are widespread in gram negative bacteria.
Iron related bacteria species, sulfate reducing
bacteria, Escherichia coli, Salmonella,
Pseudomonas, Helicobacter, Legionella and the
cyanobacteria are all gram negative bacteria.
Furthermore, acyl HSLs have been detected in
naturally occurring biofilms.
Continuous disinfection of the well
Three-oxo-acyl HSL is responsible for biofilm
formation in Pseudomonas aeruginosa, a copious
biofilm forming gram negative bacteria species.
Also, butyryl HSL (which lacks the 3-oxo
functionally) is important in biofilm dispersal.
Continuous disinfection of the well
Studies have shown that HOBr (hypobormous acid)
rapidly reacts with 3-oxo-acyl HSLs at dilute
concentrations.
Two molecules of HOBr are consumed for every 3oxo-acyl HSL molecule which is deactivated by this
process.
This reaction eliminates the ability of this signal
molecule to function properly as a cell-to-cell signal.
Continuous disinfection of the well
By selectively inactivating 3-oxo acyl HSL molecules,
an excess of the butyryl HSL is created which
encourages biofilm dispersal.
This deactivation of acyl HSL signaling molecules by
hypobromous acid is a natural method for biofilm
control.
Continuous disinfection of the well
Also, hypobromous acid is a strong antimicrobial that
inhibits biofilm formation through a cidal mechanism.
Furthermore, the reaction between the 3-oxo acyl HSLs
occurs even under conditions in which biofilm
components are present at much higher concentrations
than the acyl HSL levels.
Continuous disinfection of the well
Now you know the total solution to the number one
challenge to groundwater well performance: eliminate
biofilm forming bacteria in the well in an ongoing
manner to keep the well functioning at peak
performance and have the best water quality possible
coming into your treatment process.
Are there further benefits to keeping our
wells clean?
An applied area of microbiology that is significantly
affected by the presence of utilizable carbon is drinking
water.
Excess organic material in drinking water is associated
with growth of bacteria in the distribution system,
increased chlorine demand in finished waters, and the
formation of disinfection by-products.4
Continuous disinfection of water supply wells will benefit
the entire treatment regime and the distribution system
by drastically reducing the amount of utilizable carbon
available to bacteria.
Opportunistic Pathogens
• Specifically, Mycobacterium species, some of which are
opportunistic pathogens that may pose special risks to
immune-compromised individuals, are very resistant to
chlorine disinfection, could be controlled by limiting the
level of biodegradable organic carbon.
• Lowering the levels of biodegradable organic carbon
could be an important mechanism for reducing the public
health risk from opportunistic pathogens.5
• This same study showed that despite the application of
continuous disinfection using chlorine biofilm rapidly
developed. They concluded biofilm can rapidly form in
the presence of a 1 to 2 mg/L free chlorine residual.6
Identifying the Problem
Laboratory Testing
Well Camera
Identifying the Problem
•
•
•
•
IRB-BART and SRB-BART Tests
Down the Well Camera
Total plate count
Visual identification of the bacteria species
under a microscope
Identifying the
Problem
IRB-Bart Test
Q: Why are suspended bacteria
counts unreliable?
A: The monitoring of bacteria is tricky. Bacteria form biofilm
in natural environments. Most “nuisance” bacteria, such
as iron bacteria, are sessile, or attached to a
surface. Suspended bacteria counts provide false
security because the ratio of sessile bacteria to
suspended bacteria is 1,000,000 to 1.
http://www.edstrom.com/update.cfm?doc_id=333
Benefits of Continuous Control of Bacteria:
Prevents biofouling
Controls bacteria in wells
Eliminates clogging and blockages caused by iron
bacteria in pipes, pumps and distribution
Prevents odors caused by iron and sulfate reducing
bacteria in wells.
Provides well disinfection with a minimum of
chemical intervention
Further Recommended Reading:
Microbiology of Well Biofouling by Dr. Roy
Cullimore, Ph.D., Registered Microbiologist.
ISBN 1-56670-400-6
AWWA studies on biofilm
Sources
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1 2003 World Health Organization (WHO). Heterotrophic Plate Counts and Drinking-water Safety, page 95. Edited
by J. Bartram, J. Cotnuvo, M. Exner, A. Glasmacher. Published by IWA Publishing, London, UK. ISBN: 1 84339
025 6.
2 Ibid, page 85. J. Bartram.
3 Microbial Ecology (2000) 38:330-347. Effects of Carbon Source, Carbon Concentration, and Chlorination on
Growth Related Parameters of Heterotrophic Biofilm Bacteria, page 330. B. D. Ellis, P. Butterfield, W. L. Jones, G.
A. McFeters, A.K. Camper. Published by Springer-Verlag New York, US. DOI: 10.1007/s002489901003.
4 Ibid, page 331. B. D. Elis.
5 Applied and Environmental Microbiology, January 2000, p. 268-276. A Pilot Study of Bacterial Population
changes through Potable Water Treatment and Distribution. Cheryl D. Norton, Mark W. Le Chevallier. Published by
American Society for Mircobiology. 0099-2240/00.
6 Ibid, page 273. C. Norton.
7 Costerton W J, Lewandowski Z. Microbial biofilms. Annu Rev Biochem. 1995; 49: 711–745.
8 Sjöberg A M, Wirtanen G, Mattila-Sandholm T. Biofilm and residue investigations of detergents on surfaces of
food processing equipment. Food Bioprod Proc. 95; 73: 17–21.
9 van der Wende E, Characklis W G, Smith D B. Biofilms and bacterial drinking water quality. Wat Res. 1989;23:
1313–1322.
10 Gill J F, Chakrabarty A M. Alginate production by the mucoid Pseudomonas aeruginosa associated with cystic
fibrosis. Microbiol Sci. 1987; 4: 296–299.
11 Khoury A E, Lam K, Ellis B, Costerton J W. Prevention and control of bacterial infections associated with
medical devices. ASAIO J. 1991; 38: M174–M178.
12 Marsh P D, Bradshaw D J. Dental plaque as a biofilm. J Ind Microbiol. 1995; 15: 169–175.
13 Chaudhary A, Gupta L K, Gupta J K, Banerjee U C. Studies on slime-forming organisms of a paper mill: slime
production and its control. J Ind Microbiol Biotechnol.
14 Mattila-Sandholm T, Wirtanen G. Biofilm formation in the industry: a review. Food Rev Int. 1992; 8: 573–603.
15 Dunny G M, Winans S C., editors. Cell-cell signaling in bacteria. Washington, D.C.: ASM Press; 1999.
16 Davies D G, Parsek M R, Pearson J P, Iglewski B H, Costerton J W, Greenberg E P. The involvement of cell-tocell signals in the development of a bacterial biofilm. Science. 1998;280: 295–298.
17 http://www.edstrom.com/resources.cfm?doc_id=143
18 Baker, K H, Hegarty, J P, Redmond, B, Reed, N A, Herson, D S. Effect of Oxidizing Disinfectants on
Helicobacter pylori. Applied and Environmental Microbiology, Feb. 2002, p. 981-984.
19 Reavis, C. (2005) Journal of the American Academy of Nurse Practitioners, 17 (7); 283-9.
20 Borchardt et al, Reaction of Acylated Homoserine Lactone Bacterial Signaling Molecules with Oxidized
HaloGen Antimicrobials, Applied and Environmental Microbiology, July 2001, p. 3174-3179.
Everyone Deserves Clean Water