Materials Transactions, Vol. 46, No. 7 (2005) pp. 1636 to 1645
Special Issue on Medical, Healthcare, Sport and Leisure Materials
#2005 The Japan Institute of Metals
OVERVIEW
Antibacterial Metals —A Viable Solution for Bacterial Attachment
and Microbiologically Influenced Corrosion—
Kurissery R. Sreekumari1; *1 , Yoshihiro Sato2 and Yasushi Kikuchi1; *2
1
Joining & Welding Research Institute, Osaka University, Ibaraki, Osaka 567-0047, Japan
Department of mechanical & Physical Engineering, Graduate School of Engineering, Osaka City University,
Osaka 558-8585, Japan
2
Microbiologically Influenced Corrosion (MIC), otherwise coined as biocorrosion, is the influence of microorganisms on the kinetics of
corrosion processes of metals, minerals and synthetic materials caused by their adhesion and growth. A closer observation of the MIC failure
case analyses of engineering components showed that MIC occurs at or near welds. Preferential bacterial attack on the austenite phase leaving a
skeleton like appearance is commonly reported on welds. The initial step of this phenomenon is the attachment of bacteria, which, over a period
of time develop into a biofilm on the material surface. However, the intriguing question that remains to be answered is ‘‘Why welds are prone to
preferential MIC attack?’’ Experiments on bacterial attachment on stainless steel surfaces revealed that surface roughness plays a pivotal role.
Naturally, welds are with rough surfaces and that explains the preferential attachment of bacteria. Also, it was noticed that shape of the weld
beads, determines the extent of bacterial attachment on to their surfaces. Leaving apart the surface roughness as the major contributing factor for
the preferential bacterial attachment, studies were carried out to determine whether the underlying microstructure has any influence on it. Results
suggested that there is. There was significant difference in percentage area of bacterial attachment between base metal and weld even after
nullifying the surface roughness by polishing. Weld metal was preferred for attachment by bacteria more than base metal. Subsequent studies
using an image superimposing technique revealed that grain boundary or the austenite/ferrite interface was preferred by bacteria as their initial
attachment site. Welds have more such interfaces/or grain boundaries than base metal and thus resulting in more bacterial attachment, quickly
leading to the initiation of MIC. The influence of inclusions, energy gradient and alloying elements are also discussed as factors associated with
this phenomenon. In order to test the effect of elemental segregation occurring at grain boundaries on bacterial attachment, experiments were
carried out using sulfur enriched stainless steel welds as well as high nitrogen stainless steels. Presence of sulfur and nitrogen as alloying
elements enhanced bacterial attachment. Sulfur and nitrogen are essential elements for bacterial growth and their presence must have enhanced
bacterial attachment. This result led us to the development of antibacterial metals. The hypothesis that worked out was if essential elements
enhance attachment, toxic elements should deter it. Controlling bacterial attachment would be beneficial, both for deterring MIC and preventing
infection and maintaining hygiene, especially in hospitals and food industries. Silver and copper, the well-known toxic elements were tried as
alloying elements in stainless steel. While doing so, the material properties were kept largely in par with the silver/copper free stainless steel.
The efficiencies of these antibacterial stainless steels were tested in the laboratory and were found to resist bacterial attachment and MIC. Silver
containing stainless steels were tested in a freshwater environment as well. They were found to resist microfouling build up until a period of one
month (the maximum duration of the study). Coupon exposure studies for longer duration are being carried out in our laboratory. In order to help
in the development of high quality antibacterial metals, a base line data on the antibacterial efficacies of different candidate alloying elements are
necessary. For this purpose, various metals were tested for their antibacterial efficacy using a standard method, known as film contact method as
well as conventional coupon exposure tests. This chapter also discusses the merits and de-merits of antibacterial metals and their applications.
(Received January 24, 2005; Accepted April 6, 2005; Published July 15, 2005)
Keywords: antibacterial metals, microbiologically influenced corrosion, bacteria, corrosion, weld, stainless steels, silver, copper
1.
Introduction
Biofilm formation on surfaces of importance whether it is
for industries or biomaterials is a matter of significant
concern.1) Biofilms could be deleterious to materials, when
they induce corrosion.2) As the microorganisms grow on
substratum surfaces, they produce various metabolic byproducts, which might promote deterioration of the underlying substratum. These reactions refer to biocorrosion or
microbiologically influenced corrosion (MIC) when the
underlying substratum is a metal or metal alloy.3) Microbiologically influenced corrosion (MIC) is a serious problem
in a number of industries including power generation,
petrochemical, pulp and paper, gas transmission and shipbuilding. Conservative estimates place the direct cost of MIC
at US$ 30 to 50 billion/year.4) The magnitude of the problem
necessitates a wider attention that might encompass collaboration between established research groups or laboratories
*1Present
address: Department of Biology, Lakehead University, 955
Oliver Road, Thunder Bay, Ontario, Canada P7B 5E1
*2Professor Emeritus, Osaka University
specializing researches on various aspects of metal microbe
interactions viz. microbiology, metallurgy, civil & environmental engineering and biotechnology. The role of bacteria
and their associated biofilm play in MIC drove the attention
of scientists from the late 1970s.5) Since long, MIC has been
referred to as the cause for deterioration of various materials
and the combination of unexpected attack and rapid failure
make MIC a matter of considerable concern in many
applications.4) Whatever be the material and mechanisms
involved, one of the striking observations is the consistent
incidence of MIC at and near welds.
The formation and succession of biofilms depend on the
environmental and biological factors as well as the surface
characteristics of the materials. MIC is reported in various
materials and it is well known that microbes settle preferentially on different materials. High purity metals frequently
have low mechanical strength thus making it necessary to
alloy elements thus can improve mechanical, physical,
fabrication and corrosion characteristics. Alloys are inhomogeneous, with discontinuous compositions and anisotropic
properties from an atomic scale to a macroscopic scale. The
microscopic heterogeneity of engineered materials, whether
Antibacterial Metals —A Viable Solution for Bacterial Attachment & MIC—
created intentionally or as an artifact, is the basis for their
properties. The heterogeneity is evident on the scale of
microbes and is an important factor in MIC. Weld regions are
particularly attractive to microbes as the welding alters the
material surface characteristics.6) There are reports on the
influence of alloy composition,7) manufacturing specifications such as surface finish and heat treatments and presence
of protective coatings on MIC susceptibility.8) The topological, chemical and microstructural alterations resulted by
welding may increase the corrosion susceptibility of the
welded region.9) A majority of cooling system failures of
corrosion resistant alloys is reported to be occurring around
or within weldments.8,10–13)
The combination of physical and compositional changes
brought about by the welding process is believed to facilitate
accumulation of organics onto the surface and subsequent
colonization by bacteria.14,15) Since the report of Olsen and
Szybalski,16) the preference of weld as a site of colonization
by bacteria is evident and was correlated to the surface
roughness. Kikuchi and Matsuda17) in a review pointed out
that HAZ might show a changed internal structure and
composition and may in some circumstances act as a location
where corrosion can be preferentially initiated. Walsh4) and
the studies at Joining and welding Research Institute (JWRI),
Osaka University,18–20) showed influence of surface chemistry and microstructure on bacterial attachment on welds.
Typical MIC failure cases analyzed in JWRI, Osaka
University leaving stainless steel welds with a skeleton
appearance is shown in Fig. 1.
2.
Studies on MIC of Stainless Steel and Its Welds
Studies on bacterial adhesion on welds compared to base
metals of stainless steel showed that, there is a significant
Fig. 1 MIC on SS 304 L welds (A) Stainless steel weld showing the
skeleton type corrosion due to microbial influence (B) Stainless steel
experimental coupons showing bacteria attached adjacent to corrosion
pits.
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Fig. 2 Epifluorescence microscopic images showing the variation in
bacterial attachment on different coupons of SS 304 L (base metal and
weld (as weld or without polishing)) and graph showing the variation in
percentage area of attachment of bacteria on different coupons as a
function of exposure time. The bacterium used was Pesudomonas sp.
difference in the bacterial attachment, with welds showing
very high bacterial attachment compared to HAZ (heat
affected zone) or base metal (Fig. 2). The settlement assay
was carried out with two different bacteria both isolated from
ground water corrosive environment in Japan, viz. Pseudomonas sp. and Bacillus sp., a gram negative and positive
strain, respectively. The reasons for the preferential colonization of bacteria near the welds were thought as the
substratum roughness and difference in material composition
and therefore the surface properties.21) It is known for quite
some time that the attachment of organisms vary with the
surface roughness, with rough surfaces harboring more
attachment while the smooth less. This could again be
related to the surface free energy. As pointed by Lindner,22)
the more the surface energy, the more the chances of
attachment are. Also, as the surface energy increases, the
strength of attachment increases. This is because the adhesive
strength is the sum of the surface free energy of the solid
surface and the surface tension of the water column minus the
interfacial surface tension between the solid and liquid.
Therefore, the more the free surface energy, the more the
strength of attachment is.
Increased attachment of microbes in the welded area
especially with respect to the shape and size of the weld bead
have been studied by Amaya et al.23) They have found that,
on the weld bead, the toe possessed the maximum attachment
as compared to the top most portion of the bead (Fig. 3).
They have explained the results taking into the water
movements changes happening over the bead (coupons were
incubated inside a bioreactor (flasks) which were shaken
constantly over an incubator shaker).
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K. R. Sreekumari, Y. Sato and Y. Kikuchi
Fig. 3 Variation in percentage area of bacterial attachment on different
regions of weld (304 L SS). Experiments were conducted in the laboratory.
In a related study at JWRI, Osaka University, Sreekumari
et al.24) have observed that there are factors other than the
surface roughness playing a role to determine the bacterial
attachment on to material surfaces. This is because an
increased bacterial attachment on the welded area compared
to HAZ or base metal of stainless steel was observed (Fig. 4)
even after the surfaces were polished to 1 mm finish.24) Two
factors were thought to have influenced the attachment of
bacteria on a polished surface. They are, (1) the role of
microstructure on the bacterial attachment, and (2) the
inclusions or the re-distribution of elements in the weld
region occurring as a result of welding. Experiments that
addressed to study the role of substratum microstructure on
bacterial attachment showed that the initial attachment of
bacteria occurred largely on or near the grain boundaries or
austenite/ferrite interface (in the case of welds) (Fig. 5). It is
true that, the surface energy is different between the matrix
and the grain boundary on a substratum surface with grain
boundary having more surface energy than the matrix.25) In
addition, the concentration of certain elements such as sulfur,
phosphorus etc. are more at the grain boundary compared to
matrix, which in turn might have influenced the bacterial
attachment.24) Therefore, from these results it was suggested
that, since the bacteria attached more on the grain boundaries
and since such boundaries are more in the welded area
(length of grain boundary or austenite-ferrite interface/unit
area) compared to matrix, more attachment occurred on weld
than on base metal. The increased attachment of bacteria at
the welds over a period of time might result in MIC (Fig. 6).
In order to get more information on the preferential bacterial
attachment on the grain boundaries, as explained above, we
have studied the influence of elemental enrichment during
welding. In order to address this aspect, two sets of detailed
bacterial attachment studies were conducted, one on the
sulfur enriched stainless steel and other on high nitrogen
steels (HNS).
3.
Bacterial Attachment on Sulfur Enriched Steel
Stainless steel welds were prepared by incorporating sulfur
during welding at JWRI, Osaka University. Studies on the
bacterial adhesion on sulfur enriched stainless steel welds
showed that it is a preferred site for bacterial adhesion26)
compared to normal stainless steel weld and thus is more
susceptible to MIC.6) Sulfur is an essential element for
bacterial metabolism and therefore it could be acting as a
chemical cue to attract bacteria. The experiments were
conducted using Pseudomonas sp., an isolate from a ground
water corrosive environment in Japan (Fig. 7).
4.
Fig. 4 Epifluorescence microscopic images showing the variation in
bacterial attachment on different coupons (SS 304 L polished to 1200
mm finish) and graph showing the variation in percentage area of
attachment of bacteria on different coupons as a function of exposure time.
The bacterium used for the study was Pseudomonas sp.
Bacterial Attachment Studies on HNS
Steels containing more than 0.08 weight percent nitrogen
in ferritic matrix or 0.4 weight percent nitrogen in an
austenitic matrix are considered as high nitrogen stainless
steels (HNS),27) though nitrogen is a universal alloying
element in steels. High nitrogen concentration has both
beneficial (creep resistance, solid solution hardening, grain
growth etc.) and detrimental (various embrittlement phenomena) impacts.28) However, recently HNS are preferred
for many commercial purposes, as they possess improved
structural stability and corrosion resistance than the other
classes of steels.27) For the ‘‘nickel allergy’’, a kind of
hypersensitivity of human bodies with symptoms of inflammation, eczema and irritation on contact with nickel
containing steels,29) nickel free stainless steel, where, nickel
is replaced with nitrogen is a possible remedy.
Antibacterial Metals —A Viable Solution for Bacterial Attachment & MIC—
1639
Fig. 5 Superimposed images (epifluorescence and bright field) of base metal, and weld metal coupons of SS 304 L showing grain
boundary preference of Pseudomonas sp.
Fig. 7 Percentage area of attachment of Pseudomonas sp. on different
types of SS 304 L coupons.
Fig. 6 SEM photomicrograph of 304-L stainless steel weldmetal coupon
exposed to Pseudomonas sp. for 16 days showing a skeleton type of
corrosion.
The results of the laboratory studies conducted at JWRI,
Osaka University, where the attachment of Pseudomonas sp.
on three different materials such as AISI type 304L, 304 LN,
0.4% HNS was studied, invariably showed bacteria adhesion
is more on the high nitrogen stainless steel compared to the
other two types of materials tested (Fig. 8). The HNS
surfaces immersed in aqueous medium provides a rich
substratum for these types of microbes, as there is production
of ammonia and nitrites, which are essential compounds for
the bacteria.
The attachment of these bacteria and their growth and
metabolic activities might result in microbiologically influenced corrosion of HNS. It is also known that elemental
composition on the surfaces act as chemical cues by which
bacterial adhesion is facilitated or mitigated.30) The attached
bacteria would utilize the ammonia/nitrite formed over the
substratum surface for their metabolic activities might leave
the surface prone to localized corrosion. Among the 304L
and HNS coupons exposed to bacteria, HNS coupons showed
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K. R. Sreekumari, Y. Sato and Y. Kikuchi
,t/d
Fig. 8 Bacteria seen adhered to HNS and 304 L coupons after 16 days of
exposure to Pseudomonas sp. and percentage area of bacterial adhesion on
different coupons as a function of exposure time.
, t/d
Fig. 9
Variation in free corrosion potential as a function of exposure time.
more positive free corrosion potential (Fig. 9). Especially, in
the case of exposure to Nitrosomonas sp., the ennoblement
was significant as compared to the control material. This
shows the HNS is about to start corroding faster than the
other two materials.
5.
Antibacterial Material
Bacteria are getting attracted towards certain elements, as
they might be useful for their life via components of
metabolic activity modulators. As explained before, essential
elements such as nitrogen and sulfur attracted bacterial
settlement, meaning that there could be elements that could
reduce attachment as well, as the elements may be toxic to
them. This logic lead to the concept that, if elements those are
toxic are incorporated in a belittle quantity, just sufficient to
be sensed by these microorganisms, could give an antibacterial property to otherwise a preferred settlement material.21)
This resulted in the manufacturing of antibacterial stainless
steels. Stainless steel is the most widely used material in
industries. The forgoing section summarizes that bacteria
attach quickly onto stainless steels initiating corrosion.
Non-metallic antibacterial materials are available in the
market. However, antibacterial metals are scarce. This makes
studies on antibacterial metals challenging and promising.
Nakamura et al.31) and Yokota et al.32) have reported on the
antibacterial properties of Cu and Ag bearing stainless steels,
respectively. Antibacterial property of silver is known since
centuries. As silver is non-toxic to human beings, it has been
used for healing wounds as well as water purifier in
swimming pools and space shuttles. This makes silver as
an ideal antibacterial element. Metallic elements in stainless
steels may be difficult to ionize due to the existence of a
passive film on the stainless steel. It is presumed that only a
reduced passive film formation only occur on metallic
particles of Cu and Ag that are found on the surface of Cu
and Ag containing stainless steel.32) This would allow the
ionization of Cu and Ag, and as a result, stainless steels with
these elements exhibit antibacterial property. Yokota et al.32)
reported that, Ag bearing stainless steels exhibited significant
antibacterial property, and the corrosion resistance was as
good as normal stainless steel. Also the antibacterial efficacy
of Ag ions is several hundred times stronger than that of Cu
or Ni.32) It has also been demonstrated that Ag ions infiltrate
into cell membranes more rapidly than Cu or Ni ions.33) This
makes the amount of Ag required to obtain antibacterial
effect to very minimum in comparison with other elements
tested so far.
Antibacterial stainless steels would benefit many industries particularly food and hospital where it could reduce
infections. Therefore, AISI type 304 stainless steels containing silver were prepared (<0:039 mass%) with the help of
steel making industries and evaluated for their antibacterial
property through laboratory and field experiments.
6.
Laboratory and Field Experiments on Cu Containing
Stainless Steels
Coupon exposure studies using Cu containing stainless
steel showed a significant reduction in the bacterial adhesion
as compared to plain stainless steels (control) (Fig. 10). The
bacterial exposure studies were performed using Bacillus sp.,
an isolate from a MIC failure case analyzed in JWRI, Osaka
University, Japan. The Cu contained stainless steel was
manufactured by a steel maker in Japan that had a
collaborative research program with JWRI, Osaka University.
7.
Laboratory and Field Experiments on Ag Containing
Stainless Steels
Laboratory coupon exposure study using Pseudomonas sp.
culture of 304 SS, silver alloyed (514) and silver coated (BC)
304 SS showed, a significantly reduced bacterial settlement
on silver containing stainless steels as compared to plain
stainless steel coupons. Among the two types of silver
incorporated stainless steels, 514 showed higher resistance to
bacterial attachment than the silver coated ones (Fig. 11) The
differences among the three types of steels were found to be
statistically significant (t-test, p < 0:05). With respect to the
corrosion initiation by these bacteria on these materials, 304
coupons showed highly pitted surfaces by 30 days. Pits were
generally observed in association with the biofilm (Fig. 12).
Very less number of corrosion pits could be observed on BC
coupons. However, on the 514 coupons, the bacterial
attachment was very low and pits were almost absent
(Fig. 12). Fields without bacterial cells were common on
Antibacterial Metals —A Viable Solution for Bacterial Attachment & MIC—
1641
Fig. 10 Epiflourescence microscope images showing Bacillus sp. attached
to surfaces of different coupons after 2 days exposure (A. 304 SS base
metal B. Cu contained SS base metal C. 304 SS weld (polished) D. Cu
contained weld (polished) E. 304 SS weld (as welded) F. Cu contained
weld (as welded).
Fig. 12 Scanning Electron Microscopic images of different base metal
coupons after 30 days of exposure to Pseudomonas sp.
Fig. 11 Epiflourescence microscopic images of Pseudomonas sp. adhered
on to different base metal coupons after 6 days of exposure and graph
showing the variation in % area of adhesion of Pseudomonas sp. on
different materials.
514 coupons. On BC coupons patches supposed to be the left
over by the detached bacteria could be seen. On control
coupons, where coupons only were exposed to media, no pit
formation was observed (Sreekumari et al., 2002).
In order to find out the action of silver ions on these
bacteria, transmission electron microscope study on the cells
of Pseudomonas sp. scrapped off from the surface of silver
alloyed stainless steel coupons was performed (Fig. 13). The
images revealed that silver is getting deposited inside the
bacterial cells. The black spots inside the cells, which could
not be observed in live cells, indicated the accumulation of
silver (Fig. 14). There are different opinions about the
mechanisms of how silver affects cell death.34) One of them
is that metallic ions like Agþ or Cuþ infiltrating into the cell
membranes of the bacteria where they combine with the SH
group of the dehydrase which controls the respiration.
Usually when a metal with no biological function competes
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K. R. Sreekumari, Y. Sato and Y. Kikuchi
Fig. 13 Transmission electron micrograph of Pseudomonas sp. adhered on
silver containing stainless steel surfaces.
with or replaces a functional metal, toxicity results.35) The
study thus showed that the bacteria in contact with the surface
are the most affected ones. It would be possible then for the
cells to get attached to the already attached cells and thus
escape from the direct contact with silver. But from the
results it is clear that once the cells in contact are dead, there
is a tendency to slough off leaving patches on the substratum
surface. TEM observation showed a significant damage to the
bacterial cells especially on their cell wall. Though the
concentration of silver inside the cells could not be quantified
analytically, sites resembling metal deposition were observed
both over the cell surface and inside the cell.
Since the results of the laboratory experiments were
encouraging, Sreekumari et al. have also studied the efficacy
of silver containing stainless steels in a natural environment.
For this purpose, experiments were conducted in a fresh
water pond for about 30 days. The results also showed
encouraging results. The variation in total cultivable viable
count of biofilm bacteria in the biofilm of different coupons
over the period of time of coupon exposure showed
remarkable difference (Fig. 15). While the 304SS coupons
showed the highest number of attached bacteria, 514 and BC
showed significantly lower number of bacteria. Among the
two, BC produced the maximum impact (Fig. 15).
8.
Corrosion Potential Fluctuation in Ag Containing
Stainless Steels
Corrosion probability of silver containing stainless steels
also had been monitored in the laboratory. The free corrosion
potential during the 60-day study showed significant difference among the three types of materials. After the initial drop
in potential it increased and continued to be above the initial
Fig. 14 Transmission electron micrograph showing cell damage in
Pseudomonas sp. adhered on silver containing stainless steel surfaces (A
magnified view).
value in the case of 304 and BC coupons. However, the
potential did not show much fluctuation on the 514 coupons
throughout the study period. What was interesting is that, free
corrosion potential variation followed a similar trend as that
of bacterial adhesion. Free corrosion potential did not show
any change on medium control coupons (Fig. 16).
9.
Baseline Data on Antibacterial Efficacy of Different
Metals and Alloys
A standardized test for antibacterial efficacy, the film
contact method was used to investigate the ability of different
metals to resist bacterial attachment. Zn, Ni, Pb, Co, Mo, Zr,
Cu, Sn, and Ti were used for this purpose. Except Sn and Ti,
all other metals showed profound antibacterial property by
reducing the colony forming units (cfu) of bacteria on their
surface to less than 101 from 106 within a period of 24 hours
(Fig. 17). The test was conducted using both Escherichia coli
and Staphylococcus aureus. Two copper alloys tested (Cu–
Zn and Cu–Sn) also showed antibacterial properties by
Antibacterial Metals —A Viable Solution for Bacterial Attachment & MIC—
1643
Fig. 15 The variation in total viable count of biofilm bacteria on different
coupons exposed in a freshwater pond over a period of time.
Fig. 18 Results of the antibacterial efficacy test on different alloys. The test
strain was Staphylococcus aureus.
Fig. 16 Variation in free corrosion potential of different base metal
coupons as a function of exposure time. Coupons were exposed to
Pesudomonas sp. in the laboratory.
Fig. 19 The reduction in the cfu of Staphylococcus aureus in contact with
different metals. The observations were conducted intermittently over a
very short duration of 24 h.
Fig. 17 Results of the antibacterial efficacy test on different pure metals.
The test strain was Staphylococcus aureus.
reducing the cfu to less than 101 from 106 within an hour of
contact (Fig. 18). It was assumed that the rate of reduction
occurring on different metals will be different over a period
of shorter time intervals before reaching the final zero cfu
level within 24 h and therefore further experiments were
carried out with shorter sampling intervals of bacterial cells
in contact with the surfaces. The results are shown in Fig. 19.
From the slope of the curves, the relative antibacterial
efficacy was determined. The results showed that Pb followed
by Co and Cu were most effective metals those resisted
bacterial attachment and growth by causing mortality. Thus
these elements could be carefully considered as antibacterial
elements that could be incorporated in different alloying
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K. R. Sreekumari, Y. Sato and Y. Kikuchi
Fig. 20 Transmission electron micrographs showing Staphylococcus aureus cells observed after contact with different metals.
situations to resist bacterial attachment. This could pave way
for the development of novel antibacterial metals in future.
10.
TEM Observation for Cell Damage
Transmission electron microscopy was used to evaluate
the bacterial cell damage occurred in the case of different
antibacterial metals tested (Fig. 20). Though detailed investigation to the mechanisms involved is yet to be completed, it
was evident from the Figures that the cell damage pattern was
different for different metals.
11.
Conclusions
Bacterial attachment and the consequent biofilm formation
might be the preliminary step leading to microbiologically
influenced corrosion. It is known that surface roughness plays
a major role in enhanced bacterial attachment on welds.
Studies were carried out to investigate any other possible
factors influencing it other than surface roughness. The
results were promising and pointed out the role of microstructure on bacterial attachment. The grain boundaries or
austenite ferrite interfaces were preferred by Pseudomonas
sp. and the reasons were thought to be as the energy
difference or elemental segregation at these locations. Sulfur
enriched welds and high nitrogen stainless steel showed more
bacterial attachment compared to AISI type 304 stainless
steel. This lead to the concept of antibacterial metals by
addition of toxic elements as alloying components. Copper
and silver containing stainless steels were investigated for
their resistance to bacterial attachment and were found to be
mitigating it. Silver containing stainless steels were tested in
the field too for a period of 30 days. They were resisting
microfouling load to a significant level compared to the
normal stainless steel. Studies were also conducted on the
antibacterial efficacy of different metals and alloys to
investigate their suitability as alloying elements to make
novel antibacterial metals. The results indicated different
levels of bacterial mortality upon contact with different
metals and the TEM images of bacterial cells from the metal
surfaces showed varying degrees of cell lesions. This data
could form the base line information those could be useful
while considering the development of new antibacterial
metals.
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