The effect of octylglucoside and sodium cholate in Staphylococcus epidermidis and Pseudomonas aeruginosa adhesion to soft contact lenses.

Abstract

In this study, the effect of the natural surfactants octylglucoside and sodium cholate in inhibiting Staphylococcus epidermidis and Pseudomonas aeruginosa adhesion to conventional and silicone-hydrogel contact lenses (CL) was assessed. Hydrophobicity was also evaluated to conditioned and nonconditioned CL.
The inhibiting effect of the tested surfactants was determined through "in vitro" adhesion studies to conditioned and nonconditioned CL followed by image acquisition and cell enumeration. Hydrophobicity was evaluated through contact angle measurements using the advancing type technique on air.
Sodium cholate exhibits a very low capability to inhibit microbial adhesion. Conversely, octylglucoside effectively inhibited microbial adhesion in both types of lenses. This surfactant exhibited an even greater performance than a multipurpose lens care solution used as control. Octylglucoside was the only tested surfactant able to lower the hydrophobicity of all CL, which can explain its high performance.
The results obtained in this study point out the potential of octylglucoside as a conditioning agent to prevent microbial colonization.

Full text

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ORIGINAL ARTICLE
The Effect of Octylglucoside and Sodium
Cholate in Staphylococcus epidermidis and
Pseudomonas aeruginosa Adhesion to Soft
Contact Lenses
Lı ´VIA SANTOS, MSc, DIANA RODRIGUES, BSc, MADALENA LIRA, MSc,
ROSA ´RIO OLIVEIRA, PhD, M. ELISABETE C. D. REAL OLIVEIRA, PhD,
EVA YEBRA-PIMENTEL VILAR, PhD, and JOANA AZEREDO, PhD
Instituto de Biotecnologia e Bioengenharia, Centro de Engenharia Biolo ´gica, Universidade do Minho, Minho, Portugal (LS, DR, RO, JA),
Centro de Fı ´sica, Universidade do Minho, Minho, Portugal (ML, MECDRO), and Departamento de O´ptica e Optometria, Universidade
de Santiago de Compostela, Spain (EY-PV)
ABSTRACT
Purpose. In this study, the effect of the natural surfactants octylglucoside and sodium cholate in inhibiting Staphylococcus
epidermidis and Pseudomonas aeruginosa adhesion to conventional and silicone-hydrogel contact lenses (CL) was
assessed. Hydrophobicity was also evaluated to conditioned and nonconditioned CL.
Methods. The inhibiting effect of the tested surfactants was determined through “in vitro” adhesion studies to conditioned
and nonconditioned CL followed by image acquisition and cell enumeration. Hydrophobicity was evaluated through
contact angle measurements using the advancing type technique on air.
Results. Sodium cholate exhibits a very low capability to inhibit microbial adhesion. Conversely, octylglucoside
effectively inhibited microbial adhesion in both types of lenses. This surfactant exhibited an even greater performance
than a multipurpose lens care solution used as control. Octylglucoside was the only tested surfactant able to lower the
hydrophobicity of all CL, which can explain its high performance.
Conclusions. The results obtained in this study point out the potential of octylglucoside as a conditioning agent to prevent
microbial colonization.
(Optom Vis Sci 2007;84:429–434)
Key Words: octylglucoside, sodium cholate, Staphylococcus epidermidis, Pseudomonas aeruginosa, inhibition of
adhesion
O
kinds of lenses commercially available. However, soft CL are the
most common. These lenses are composed of hydrophilic mono-
mers such as hydroxyethylmethacrylate, N-vynil pyrrolidone,
methacrylicacid,andpolyvinylalcohol.1,2Recently,theintroduction
of silicone-containing hydrogel CL having the same comfort and sig-
nificantlyhigheroxygenpermeabilitythanconventional-hydrogelhas
resultedinanewgenerationofsoftCL.Thehighoxygenpermeability,
onaccountofthesiloxanecomponent,makesitpossibletowearthese
lenses on a continuous basis for 30 days.1–3
ver the last few decades the number of contact lens (CL)
wearershasgrown rapidly because of the esthetic, ther-
apeutic, visual, and comfort reasons. There are several
The occurrence of CL associated keratitis as well as other ocular
complications has been a target of continuous research in several
fields. When a CL is placed in the eye, the lachrymal tear compo-
nents are adsorbed on its surface, building an organic substrate for
subsequent microbial adhesion.4In particular, when the corneal
tissues are no longer intact due to hypoxic conditions or mechan-
ical friction, microbes can invade the cornea and induce an ocular
infection.4,5So,thedevelopmentofstrategiessuchastheimprove-
ment of lens materials and lens care systems that avoid or decrease
CL associated infections are very important aspects of soft CL
research. The incorporation of surfactants in the lens care systems
is useful not only to solubilize the organic tear film components
1040-5488/07/8405-0429/0 VOL. 84, NO. 5, PP. 429–434
OPTOMETRY AND VISION SCIENCE
Copyright © 2007 American Academy of Optometry
Optometry and Vision Science, Vol. 84, No. 5, May 2007

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adsorbed on lens surface, but also to disrupt microbial mem-
branes.6Nonetheless, surfactants are also able to modify the CL
surface properties and thus may inhibit microbial adhesion.7,8
Octylglucoside is a nonionic and nontoxic surfactant which be-
longs to the alkylglucoside class,9being frequently used to solubi-
lize membrane bound proteins in their native state. Sodium
cholate is a negatively charged (anionic) and nontoxic surfactant
that belongs to the bile salts class. The use of sodium cholate has
already been tested and when used below 0.5% (w/v)10is harmless
to the ocular tissues. The aim of this work is to compare the effect
of two natural surfactants, octylglucoside and sodium cholate and
one commercial multipurpose lens care solution which incorpo-
rates the surfactant poloxamine in inhibiting the adhesion of one
strain of Staphylococcus epidermidis and one of Pseudomonas aerugi-
nosa to conventional hydrogel and silicone-hydrogel CL. These
bacterial species are two of the most frequent pathogens4,5,11in-
volvedintheoccurrenceofmicrobialkeratitisandthusconsidered
representative for this study. The efficacy of the surfactants was
tested on CL belonging to each FDA group.
MATERIALS AND METHODS
Contact Lenses
CL from each of the four FDA groups were used in this study.
Group I materials are nonionic and possess a water content lower
than 50%. Group II materials have water content of 50% or
greater and are nonionic. Group III lenses are made of low-water
content ionic materials and, finally, group IV lenses consist of
high-water content ionic materials. The properties and commer-
cial designations of the lenses used in this study are detailed in
Table 1.
Surfactants and Multipurpose Solutions
The tested surfactants were n-octylglucoside [n-octyl-B-D-
glucopyranoside] (Sigma Aldrich, Germany), a nonionic surfac-
tant, and sodium cholate (Sigma Aldrich, Germany), an anionic
surfactant. The physical–chemical properties of these surfactants
aredetailedinTable2andtheirstructuresrepresentedinFigures1
and 2. The concentration used for both was half of their respective
critical micelle concentration. Surfactant solutions were prepared
with sterile deionized water and used immediately after prepara-
tion. The multipurpose lens care solution was Renu Multiplus
withHydranate(Bausch&Lomb,US).Thissolutioniscomposed
of 1% poloxamine (nonionic surfactant), 0.0001% Dymed (cat-
ionic biocide), 0.03% Hydranate (protein remover), and ethylene
diamine tetraacetic acid (EDTA).
Bacterial Strains and Growth Conditions
The strains used in this study were the clinical isolate S. epider-
midis 9142, and P. aeruginosa ATCC 10,145 (ATCC, American
Type Collection Culture). S. epidermidis 9142 is a well-known
producer of the major surface polysaccharide promoting coagulase
negative staphylococci adherence and biofilm formation, referred
FIGURE 1.
Schematic representation of the sodium cholate molecule.
FIGURE 2.
Schematic representation of the octylglucoside molecule.
TABLE 1.
Contact lenses and their properties
CategoryMaterial
Commercial
nameManufacturer
FDA
groupCharge
Water
content (%) Surface treatment
Conventional
hydrogel
Nelfilcon A
Etafilcon A
Focus Dailies
Acuvue
CIBA Vision
Johnson and Johnson
Visioncare
CIBA Vision
II
IV
Nonionic
Ionic
69.0
58.0
No
No
Silicone
hydrogel
Lotrafilcon BO2Optix
I Nonionic33.025 nm plasma coating
with high refractive
index
Plasma oxidation
producing glassy
islands
Balafilcon A PurevisionBausch & Lomb IIIIonic 36.0
TABLE 2.
Properties of octylglucoside and sodium cholate
Surfactant
CMC
(% w/v)
Molecular weight
(g/mol)
Chemical
formula
Octylglucoside
Sodium cholate
0.60
0.73
292.38
430.53
C14H28O6
C24H39O5Na
CMC, critical micelle concentration.
430Bacterial Adhesion to Soft Contact Lenses—Santos et al.
Optometry and Vision Science, Vol. 84, No. 5, May 2007

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to as either polysaccharide intercellular adhesin or by its chemical
composition, poly-N-acetyl glucosamine. This strain was kindly
provided by Gerald B. Pier, Harvard Medical School, US, and its
adhesion and biofilm formation capabilities were characterized in
previousstudies.12P.aeruginosaATCC10,145wasobtainedfrom
the ATCC and was isolated by F. Kavanagh (Merck Sharp and
Dohme).
A 4°C culture stock was inoculated into an Erlenmeyer flask
containing 10 mL of tryptic soy broth (TSB, Merck, Germany)
and incubated for 24 h at 37°C. After this period, 1 mL of the
culture suspension was transferred to a second Erlenmeyer flask
containing 30 mL of TSB and incubated for 18 h at 37°C in order
toobtainamidexponentialgrowthculture.Cellswereharvestedby
centrifugation (15 min, 5000g) and washed twice with Millipore
water. Finally, the cells were resuspended in phosphate buffered
saline (PBS: 8 g L?1NaCl, 0.2 g L?1KCl, 0.2 g L?1KH2PO4,
1.15gL?1Na2HPO4)andtheconcentrationadjustedto1?1010
CFU/mL. Before the experiments, cell viability was evaluated
through plating and colony forming units enumeration. The re-
sults showed that both strains maintain their viability after 18 h of
incubation (data not shown).
Contact Angle Measurements
The CL relative hydrophobicity was determined through con-
tact angle measurement with Millipore water using the advancing
contact angle as described by Bruinsma et al.4Contact angles were
measuredonnonconditionedandconditionedCLusingtheappa-
ratus OCA 20 (Dataphysics). The conditioning process was per-
formed by simple immersion of the lenses in the surfactant
solution, or in the multipurpose lens care solution for a 16-h pe-
riod. For the measurements, lenses were cut into four pieces and
placed on a microscope slide. The excess of moisture was removed
bygentleblottingwithabsorbentpaper.Thesemeasurementswere
repeated 15 times per contact lens material at room temperature
(22°) and a humidity of 50% ? 3%.
Adhesion Assays and Image Acquisition
The method used to assess bacterial adhesion to CL was the
static adhesion assay. Each CL was immersed in a well of a 24-well
microtiter plate containing 1 mL of a cell suspension (6 ? 1010
CFU/mL) prepared in PBS. The tissue microtiter plate was then
incubated for 2 h at 37°C and after this period each CL was re-
moved and washed three times by immersing the lens in clean
sterile PBS solution for 10 s. This washing step was carefully per-
formed to remove only the cells that were suspended in the liquid
interface formed along the lens surface and to minimize adhered
cellsdetachmentasdescribedbyCercaetal.13Theadhesionassays
were performed with non-conditioned (control) and conditioned
CL. The lenses were conditioned by simple immersion in the sur-
factantsolutions,orinthemultipurposelenscaresolutionfor16h
followed by the adhesion assay. The adhesion assays were made in
triplicate and repeated twice for each CL type and each condition-
ing agent.
After the adhesion assays, two opposite edges of each CL were
cut to flatten the surface and the lens mounted on a microscope
slide. Cell quantification was performed using a phase contrast
microscope (Carl Zeiss, Germany) coupled to a 3 CCD video
camera (Carl Zeiss) that acquires images at a magnification of
1622? with a resolution of 1300 ? 1030 pixels and 20 images
were randomly take from each CL. To eliminate image interfer-
ences, the background was captured and subtracted from the
original image. Cells were enumerated using the Sigma Scan Pro
program and for the magnification used 1 cm2was equivalent to
3906.25 captured images.
The%ofadhesioninhibitionbyeachsolutionwascalculatedas
follows:
% Inibition
??
#cells adhered to non-conditioned CL
? #cells adhered to conditioned CL
#cells adhered to non-conditioned CL?? 100
Statistical Analysis
Dataanalysiswasperformedusingthestatisticalprogram,SPSS
(Statistical Package for the Social Sciences). After the evaluation of
data distribution by K-test, contact angles data were compared
using the parametric test analysis of variance (ANOVA) with
Tukey’s pairwise comparison whereas the extent of adhesion was
compared by the nonparametric Mann–Whitney U test. All tests
were performed with a confidence level of 95%.
RESULTS
Contact Angles
Figure 3 presents the water contact angle values of the studied
CL.AccordingtovanOssandGiese,14asurfacecanbeconsidered
hydrophobic if the water contact angle exceeds 50° and hydro-
philic if it is inferior to 50°. Thus, contact angles of noncondi-
tioned CL showed that silicone hydrogel CL are hydrophobic,
whereas the conventional hydrogel CL are hydrophilic with
Nelfilcon A being the most hydrophilic one (Etafilcon A, p ?
0.023; Balafilcon A, p ? 0.000; Lotrafilcon B, p ? 0.000).
After conditioning the CL with the surfactants or the multipur-
pose solution, the contact angles generally decreased except for
FIGURE 3.
Water contact angles of non-conditioned and conditioned CL measured at
room temperature (one-way ANOVA, Tukey’s with 95% confidence
level). Error bars represent standard deviations.
Bacterial Adhesion to Soft Contact Lenses—Santos et al.431
Optometry and Vision Science, Vol. 84, No. 5, May 2007

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Balafilcon A (p ? 1.00) and Etafilcon A conditioned with sodium
cholate, which increased (p ? 0.000). This result indicates that
sodium cholate is not such an effective surface agent as octylglu-
coside or the multipurpose solution.
Bacterial Adhesion to Nonconditioned CL
Static adhesion results can be observed in Figures 4 and 5. For
both tested strains it was observed that bacterial adhesion occurred
in larger extent to silicone hydrogel CL than to conventional hy-
drogel CL. Adhesion of S. epidermidis 9142 and P. aeruginosa
ATCC 10,145 to Balafilcon A and Lotrafilcon B was signifi-
cantly greater than that observed in Etafilcon A and Nelfilcon A
(p ? 0.05).
Adhesion to Conditioned CL and Inhibition
of Adhesion
Figures 4 and 5 and Table 3 present, respectively, the results of
microbial adhesion to conditioned CL and the % of inhibition
promoted by the surfactant solutions and the multipurpose solu-
tion. Generally, octylglucoside exhibited the best performance for
bothstrainsandthetestedCL.Octylglucosidewasveryeffectivein
inhibiting S. epidermidis adhesion, because all CL conditioned
withthissurfactantshowedasignificantdecreaseinthenumberof
adhered cells (Etafilcon A, p ? 0.021; Nelfilcon A, p ? 0.021;
Balafilcon A, p ? 0.020; and Lotrafilcon B, p ? 0.009). This
surfactant was also effective against P. aeruginosa in all lenses
(Etafilcon A, p ? 0.008; Balafilcon A, p ? 0.020; and Lotrafilcon
B, p ? 0.020) except for Nelfilcon A, probably because P. aerugi-
nosa showed very low levels of adhesion to this material. Concern-
ing sodium cholate, this surfactant only inhibited the adhesion of
the S. epidermidis strain to Balafilcon A CL (p ? 0.021) and of P.
aeruginosa to Lotrafilcon B. The multipurpose solution, did not
demonstrated a significant inhibition effect in S. epidermidis adhe-
sion with the exception of Lotrafilcon B, whereas for P. aeruginosa
thiseffectwasrelevantinBalafilconA(p?0.006)andLotrafilcon
B (p ? 0.014).
DISCUSSION
In this work, the preconditioning effect of two surfactants and
one multipurpose solution on bacterial adhesion to CL was evalu-
ated. The adhesion assays were performed on unworn CL, how-
ever, it must be considered that in situ the CL become rapidly
conditioned with adsorbed components of the tear film such as
proteins and lipids,15–17which may influence lens surface proper-
ties and thus microbial adhesion. Nevertheless, this fact does not
invalidate the methodology used, because the purpose of this work
is to study the CL preconditioning as a way to promote the inhi-
bition of adhesion and as a palliative strategy to avoid ocular com-
plications. The modification in CL surface hydrophobicity due to
surfactant conditioning was also evaluated.
FIGURE 4.
Number of cells of Staphylococcus epidermidis adhered to noncondi-
tioned and conditioned CL with octylglucoside, sodium cholate, and the
multipurpose lens care solution. *Statistically superior compared to the
control (Mann–Whitney U Test). Error bars represent standard deviations.
FIGURE 5.
Number of cells of Pseudomonas aeruginosa adhered to nonconditioned
and conditioned CL with octylglucoside, sodium cholate, and the multi-
purpose lens care solution. *Statistically different compared to the control
(Mann–Whitney U Test). Error bars represent standard deviations.
TABLE 3.
Inhibition of adhesion (average values) promoted by octylglucoside, sodium cholate, and the multipurpose solution (% ?
standard deviation)
Etafilcon ANelfilcon A Balafilcon ALotrafilcon B
Staphylococcus epidermidis 9142
Octylglucoside
Sodium cholate
Multipurpose solution
Pseudomonas aeruginosa ATCC 10145
Octylglucoside
Sodium cholate
Multipurpose solution
65.5 ? 24.4
?45.6 ? 3.2
5.6 ? 1.8
68.0 ? 8.6
42.8 ? 11.7
?2.8 ? 0.5
68.2 ? 23.7
64.7 ? 21.8
42.2 ? 10.2
55.3 ? 3.0
14.5 ? 3.0
35.7 ? 1.5
37.6 ? 4.7
20.3 ? 1.3
?14.1 ? 0.6
?63.6 ? 32.7
4.6 ? 0.65
?96.6 ? 33.7
30 ? 6.6
7.8 ? 0.26
47.0 ? 2.8
39.0 ? 2.6
37.0 ? 0.5
51.5 ? 0.08
432Bacterial Adhesion to Soft Contact Lenses—Santos et al.
Optometry and Vision Science, Vol. 84, No. 5, May 2007

Page 5

Contact angle measurements (Fig. 3) revealed that the silicone
hydrogel CL, Balafilcon A and Lotrafilcon B are hydrophobic,
whereas conventional hydrogel CL are hydrophilic. Silicone-
hydrogel CL hydrophobicity was already demonstrated and ex-
plained by the presence of silicone in the lens matrix which is a
hydrophobic monomer. Contact angles have also revealed that the
surfactants and the multipurpose solutions are capable of modify-
ing the CL surface properties. Generally, conditioned CL resulted
in a decrease of the water contact angle with the exception of
Balafilcon A and Etafilcon A with sodium cholate. It is commonly
accepted that surfactant adsorption depends mainly on the surfac-
tant structure and surfactants with longest alkyl chain usually ad-
sorb the most.9Sodium cholate exhibits a very different chemical
structure from octylglucoside and poloxamine which may explain
its lower performance. In fact, this bile salt is a planar molecule,
(Fig. 1) punctuated with hydrophilic groups conversely to octyl-
glucoside or poloxamine, which exhibit well defined hydrophilic
and hydrophobic domains. The adsorption of octylglucoside and
poloxamineonthelenssurfacethroughthehydrophobicmoieties,
exposing the hydrophilic groups to the aqueous media certainly
contributed to the decrease of the hydrophobicity of all CL.
Regarding bacterial adhesion to nonconditioned lenses,
silicone-hydrogel CL revealed to be more prone to S. epidermidis
and P. aeruginosa adhesion than conventional hydrogel CL. These
results seem to be strongly related with the lens surface hydropho-
bicity. In a previous study we have demonstrated that silicone-
hydrogel CL are more prone to S. epidermidis and P. aeruginosa
adhesion than conventional hydrogel,18corroborating other “in
vitro” studies using different microorganisms.19–21
Concerning the conditioning effect of the surfactants or the
multipurpose solution, this study showed that the modification of
the surface properties, particularly the decrease of hydrophobicity
not always leads to a decrease in bacterial adhesion. It is well estab-
lished that surfactants are able to modify the surface properties of
materials and thus influence adhesion,22–24however in this study
only CL conditioned with octylglucoside, revealed a significant
decrease of hydrophobicity as well as a reduction in the extent of
microbial adhesion compared with the control (Figs. 4 and 5, and
Table3).Thisresultismostprobablyrelatedwiththeamphiphilic
properties of the surfactant molecules as well as their structure.
Accordingly, well-defined hydrophilic/hydrophobic regions of
both octylglucoside and poloxamine enabled them to coat the lens
in a uniform and consistent way, in opposite to sodium cholate.
SodiumcholateonlyinhibitedmicrobialadhesioninBalafilconA,
although it did not reduce the lens hydrophobicity. This CL has a
nonuniform surface, presenting “silicate islands” and probably so-
dium cholate molecules were adsorbed between these “islands”
building a physical barrier against bacterial adhesion. The multi-
purpose solution was effective in inhibiting the adhesion of the S.
epidermidis strain to Lotrafilcon B and the P. aeruginosa strain to Bal-
afilconAandLotrafilconB.Abetterperformanceofthissolutionwas
expected since it incorporates the surfactant poloxamine which
possesses antimicrobial properties25,26and in addition, has a higher
surfactant concentration than the tested surfactant solutions. Never-
theless, the presence of other complex components in the multipur-
pose solution may have contributed for lowering its performance.
This study provides evidence that octylglucoside can effectively
inhibit bacterial adhesion either to conventional or to silicone-
hydrogelCL.Thisfindingismostlikelyrelatedtotheiramphiphi-
lic properties as their molecular structure. Many other condition-
ing agents such as poly(ethylene glycol),27salycilate28and
heparin29have been tested on CL with the aim of reducing micro-
bial adhesion. Still, octylglucoside has the increased advantage of
inhibitingadhesionandbeingnontoxicandinexpensive.Despitethe
good results obtained for octylglucoside more experiments must be
performed to test if the inhibiting capability of octylglucoside is af-
fected by other chemical components that may be present in multi-
purpose solution such as biocides and preservatives.
ACKNOWLEDGEMENTS
The authors fully acknowledge the financial support of the Portuguese Foun-
dation for Science and Technology (FCT) through the project POCTI/FCB/
44,628/2002 and also the grant BD 19,679/2004 (FCT).
Received March 1, 2006; accepted January 10, 2007.
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Joana Azeredo
IBB—Instituto de Biotecnologia e Bioengenharia
Centro de Engenharia Biolo ´gica
Universidade do Minho, Campus de Gualtar
4710-057 Braga, Portugal
e-mail: jazeredo@deb.uminho.pt
434Bacterial Adhesion to Soft Contact Lenses—Santos et al.
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