Bacterial adherence of Staphylococcus epidermidis to intraocular lenses: a bioluminescence and scanning electron microscopy study

PURPOSE

To analyze and compare the adherence of Staphylococcus epidermidis to intraocular lenses (IOLs) made of five different biomaterials (native or heparinized polymethylmethacrylate, silicone, hydrophilic acrylic, or hydrogel) and to detail the different steps and mechanisms of bacterial adhesion to a polymer.

METHODS

A clinical strain carrying the intercellular adhesion (ica) locus was used. In a previous study, the extent of bacterial binding was measured by counting. In this study, two different techniques, bioluminescence and scanning electron microscopy (SEM), were used to analyze the accuracy of each one, to obtain a comparison between the various IOLs, and to complete previous observations. The results were compared using both the Kruskal-Wallis and the Mann-Whitney nonparametric tests.

RESULTS

Bacterial adhesion was statistically weakest on hydrogel and then on hydrophilic acrylic polymer. Adhesion depended on the hydrophobicity or hydrophilicity of the biomaterials. Slight differences were found between the two methods, and these differences are explained. Furthermore, SEM observations highlighted two different patterns of bacterial adhesion (isolated bacteria and clusters of bacteria), assuming that hydrophobic IOLs (silicone and PMMA) probably facilitate bacterial colonization and biofilm production.

CONCLUSIONS

Attachment mechanisms may be different in each case, depending on the polymer material and the infecting organism, because there are various types of behavior among S. epidermidis strains. Hydrophilic polymer surfaces (hydrogel and probably hydrophilic acrylic) seem to be useful in avoiding the development of bacterial colonies and hence in preventing endophthalmitis. Fewer bacteria were attached, demonstrating inhibition or delay in bacterial colonization.

Antimicrobial activity and interference of tobramycin and chloramphenicol on bacterial adhesion to intraocular lenses

The antimicrobial activities of tobramycin and chloramphenicol were evaluated by determining minimum inhibitory and bactericidal concentrations against Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, group A, group B and group G streptococci, Klebsiella spp., Stenotrophomonas maltophilia and ciprofloxacin-resistant and -susceptible Pseudomonas aeruginosa, as well as by evaluating interference on adhesion of slime producer strains of S. aureus and P. aeruginosa to intraocular lens from tobramycin and chloramphenicol pharmaceutical products by scanning electron microscopy. Chloramphenicol was more active against Gram-positive bacteria than was tobramycin, which instead showed higher activity against ciprofloxacin-susceptible P. aeruginosa. Treatment of lenses with the antimicrobial products eradicated the bacterial biofilm, which was already notably reduced after 5 min. This activity was more pronounced for chloramphenicol against S. aureus and for tobramycin against P. aeruginosa. Bacterial adhesion was also significantly reduced when lenses colonized by P. aeruginosa were treated with chloramphenicol, even if they were resistant to this drug. In conclusion, the tested drugs showed marked antibacterial activity, particularly by interfering with bacterial biofilms. The data obtained in this study suggest a specific use of chloramphenicol in topical prophylaxis aimed at avoiding bacterial contaminations. However, further specific in vivo studies are needed to confirm these data.

Effekt einer neuen Oberfl�chenbehandlung von Intraokularlinsen aus Silikon durch ein Fluoralkylsilan auf das Adh�renzverhalten Endophthalmitis-relevanter Bakterien in vitro

INTRODUCTION

Dynasilan is a fluoroalkylsilan which is able to bind to surface active molecules of intraocular lenses (IOLs), thereby offering a new option for surface modification of silicone lenses. The purpose of this in vitro study was to investigate the influence of this new surface treatment on the adherence of two typical endophthalmitis-inducing bacteria ( Staphylococcus epidermidis, Propionibacterium acnes).

MATERIALS AND METHODS

A total of 14 Dynasilan-treated and 14 untreated silicone lenses were incubated at 37 degrees C for 24 h in brain heart infusion broth (10(8) CFU/ml) either with Staphylococcus epidermidis or with Propionibacterium acnes for 1 h. Subsequently, the adherent bacteria were resuspended using ultrasonification at 35 kHz for 3 x 45 s. After a dilution series and incubation at 37 degrees C for 24 h or 3 days the colonies were counted.

RESULTS

On untreated IOLs incubated with Staphylococcus epidermidis the average number of bacteria was 3.6 x 10(7)/ml, and on treated IOLs the number of counted colonies was reduced to 1.09 x 10(7)/ml. Incubated with Propionibacterium acnes the average number of adherent bacteria on untreated IOLs was 4.75 x 10(4)/ml and on modified IOLs the number was reduced to 2.94 x 10(4)/ml.

CONCLUSION

Dynasilan surface treatment may reduce the adherence of Staphylococcus epidermidis and Propionibacterium acnes on silicone intraocular lenses. Further studies regarding the stability of this treatment, its biocompatibility and influence on lens epithelial cell adhesion are in progress.

Bacterial adhesion to rigid and foldable posterior chamber intraocular lenses: in vitro study

PURPOSE

To determine the in vitro bacterial adherence to intraocular lenses (IOLs) routinely used at 1 center.

SETTING

University Hospital of Vienna, Vienna, Austria.

METHODS

Four types of rigid IOLs (hydrophobic poly[methyl methacrylate] [PMMA] and hydrophilic heparin-surface-modified PMMA) and 5 types of foldable intraocular lenses (hydrophobic silicone, hydrophobic acrylic, and hydrophilic acrylic) were used in the experiment. Under standardized conditions, the IOLs were contaminated with 2 strains of Staphylococcus epidermidis. A sonication method and impression method were used for quantification. The mean bacterial density per lens type (colony forming units/mm(2)) was compared.

RESULTS

With both germs and both quantification methods, more bacteria was found on hydrophobic lenses than on IOLs with hydrophilic surfaces (P =.001). The Alcon AcrySof and Askin UV80F IOLs had the greatest and the Corneal Acrygel and Bausch & Lomb Hydroview IOLs the least affinity to these microorganisms.

CONCLUSION

The data suggest that hydrophilic IOLs can help reduce the rate of postoperative endophthalmitis as a result of their surface properties.

In vivo study of bacterial adhesion to five types of intraocular lenses

PURPOSE

To determine in vivo behavior of the ability of the Staphylococcus epidermidis strain (American Type Culture Collection [ATCC] 14990) to attach to 120 intraocular lenses (IOLs) made of five different biomaterials: fluorine polymethylmethacrylate (PMMA), heparinized PMMA, silicone, hydrophobic acrylic, and hydrogel. The pig was chosen as an animal model of endophthalmitis, after a bibliographical analysis and a personal study of its aqueous humor composition.

METHODS

Crystalline lenses from 90 domestic pigs were removed aseptically and replaced with previously infected IOLs. The animals were killed 24 hours, 72 hours, and 1 week after implantation of the IOLs. The extent of bacterial binding was then measured by counting. Results were compared with a two-factor analysis of variance (ANOVA 2), confirmed by the Kruskal-Wallis nonparametric test.

RESULTS

The extent of bacterial binding (expressed as bound bacteria per area unit) was found to range in increasing order from hydrogel, to fluorine PMMA, to hydrophobic acrylic, to heparinized PMMA, to silicone polymer. Comparison of pairs of materials showed statistically significant differences, except between hydrogel and fluorine PMMA.

CONCLUSIONS

To the authors' knowledge, no study has been published so far concerning the in vivo evolution of populations of bacteria adhering to different intraocular materials. Bacterial adhesion to the implant surface must therefore depend on the hydrophobicity or hydrophilicity of the biomaterial. Adhesion is also affected by the nature of the surrounding medium. Because of its complexity, the latter appears to be very difficult to model, thus making in vivo studies essential.

Effect of aminoglycosides (sub-MICs) on adherence of coagulase-negative Staphylococci to intraocular lens surface

The authors evaluated the in vitro effects of subinhibitory concentrations (sub-MICs) of aminoglycosides (gentamicin, netilmicin and tobramycin) on the adherence of coagulase-negative staphylococcus to intraocular lens (PMMA, acrylic and heparin) surface. The five strains of coagulase-negative Staphylococcus epidermidis used (S. epidermidis IMe7, IMe11, IMe27, IMe29 and IMe31) were tested for their ability to produce slime. The minimum inhibitory concentrations (MIC) indicated high susceptibility in vitro to the antibiotics and homogeneous values. The adhesion tests without antibiotics (K1, K2 and K3) for every time considered (30 min, 60 min and 180 min) and for all examined strains showed more constant adhesive activity on the surface of acrylic intraocular lens (IOLs) than on the surface of heparin IOLs. The aminoglycosides tested were able to reduce adhesivity by coagulase-negative S. epidermidis slime to the IOL surfaces, even at sub-MICs. The documentation obtained by scanning electron microscope shows the growth of a strain of S. epidermidis IMe11 after 180 minutes of contact which remains adherent to the surface of the acrylic IOLs.

Effect of vancomycin on Staphylococcus epidermidis adherence to poly(methyl methacrylate) intraocular lenses

PURPOSE

To study the adherence of Staphylococcus epidermidis in variable loads (10(8) cfu/mL and 10(3) cfu/mL) to poly(methyl methacrylate) (PMMA) intraocular lenses (IOLs) and to evaluate the effect of vancomycin treatment on S epidermidis adherence to the IOL.

SETTING

L.V. Prasad Eye Institute, Hyderabad, India.

METHODS

The study was designed in 2 parts. Phase I: Twelve PMMA IOLs were soaked in a solution of S epidermidis, randomized to 10(8) cfu/mL or 10(3) cfu/mL. They were rinsed or rinsed and vortexed and cultured. Phase II: Twelve IOLs were treated with vancomycin (10 mg/mL), randomized to before and after treatment with S epidermidis.

RESULTS

Staphylococcus epidermidis adhered to all portions of the IOL with 10(8) cfu/mL and 10(3) cfu/mL bacterial loads. Treatment with vancomycin reduced S epidermidis adherence.

CONCLUSION

Pretreatment of an IOL with vancomycin or a suitable antibiotic agent appears to reduce bacterial adherence to the IOL. Placement of a sustained-release device that could release an antibiotic agent over a specific period, reducing the incidence of postcataract endophthalmitis, should be studied.

[Enterococcal endophthalmitis following cataract surgery]

BACKGROUND

Postoperative endophthalmitis can be subdivided into acute and chronic forms which are typically caused by different organisms. Enterococcus faecalis is an organism which normally causes an acute form of endophthalmitis.

PATIENTS AND METHODS

We report on four cases of different forms of endophthalmitis following cataract extraction and intraocular lens (IOL) implantation who had been referred to our institution between 1998 and 2001. Enterococcus faecalis was the causative organism in all of them.

RESULTS

Two patients presented with an acute form and were immediately treated in our hospital after symptom onset utilizing pars plana vitrectomy with and without IOL explantation. The two other patients were initially treated with subconjunctival and/or systemic antibiotics and steroids over a period of about two months before referral to our hospital. After initial improvement the inflammation exacerbated in these two patients and vitrectomy with or without IOL and capsular bag explantation was performed. The explanted IOL and capsular bag of one patient were examined using scanning electron microscopy and it was shown that the enterococci were adherent to the IOL and the capsular bag.

CONCLUSION

Enterococcus faecalis can be the causative organism both of an acute and of a recurrent form of postoperative endophthalmitis. The recurrent form may be caused by organisms which tend to adhere to the IOL and the capsular bag. This should be kept in mind when considering different treatment options.

In-vitro study of bacterial adherence to different types of intraocular lenses

The aim of this study was to determine the adherence of Staphylococcus epidermidis to intraocular lenses made of five different biomaterials: polymethylmethacrylate (PMMA), heparinized PMMA, silicone, hydrophilic acrylic, and hydrogel. The extent of bacterial binding was measured by counting. The results were compared using a one-factor variance analysis. Adherence was weakest on hydrogel and strongest on the silicone polymer. Bacterial adherence to the implant surface must therefore depend on the hydrophobicity or hydrophilicity of the biomaterial.

Elucidation of antibiotic effectiveness against Staphylococcus epidermidis during intraocular lens implantation

The effect of various antimicrobial agents commonly used in irrigating solutions on the hydrophobicity and adherence of Staphylococcus epidermidis ATCC 14990 was investigated. The longest post-antibiotic effect (PAE=3.2 h) was obtained with gentamicin followed by ciprofloxacin (2.7 h), clindamycin (2.2 h), ceftazidime (1.8 h) and vancomycin (1.6 h). The post-antibiotic effect on surface hydrophobicity of cells previously treated with gentamicin, ciprofloxacin, or clindamycin for 120 min resulted in a substantial decrease in affinities to hexadecane (31.4, 28.5 and 27%, respectively) compared with control untreated cells. Less effect was noted with cells previously treated with ceftazidime or vancomycin (20.5 and 15.8%, respectively). Similar but less marked results were obtained when the cells were exposed to antibiotics for 30 or 60 min. The post-antibiotic effect on adherence of cells to both intraocular lenses and to epithelial cells showed that adherence to lenses decreased as the time of exposure to antimicrobial agents increased. Adherence was greatly diminished with cells treated with gentamicin or ciprofloxacin compared with control untreated cells. Adherence was less affected by clindamycin, ceftazidime and vancomycin. The data supported the use of antimicrobial agents in irrigating solution during intraocular surgery, since, reduced adherence (colonization) and might result in a lower incidence of endophthalmitis.

Bacterial adherence to polymethylmethacrylate posterior chamber intra ocular lenses

PURPOSE

Bacterial adherence to intraocular lenses (IOLs) has been incriminated in the pathogenesis of postoperative endophthalmitis. Staphylococcus epidermidis is the most common organism isolated. We studied the in-vitro adhesion of Staphylococcus epidermidis to Polymethylmethacrylate (PMMA) IOLs and the effect of duration of exposure to adherence.

METHODS

Two groups of 10 IOLs each were incubated in Staphylococcus epidermidis suspension for 2 minutes and 20 minutes respectively. Adhesion of bacterial cells was determined by counting the number of viable bacteria attached to IOLs.

RESULTS

The mean bacterial adherence with 2 minutes incubation was 12,889 +/- 7,150 bacteria/ IOL and with 20 minutes incubation was 84,226 +/- 35,024 bacteria/IOL (P< 0.01).

CONCLUSION

Our results show that Staphylococcus epidermidis adheres to PMMA IOLs in vitro and the degree of adherence is less for shorter duration of exposure. We conclude that viable bacteria irreversibly adherent to IOLs may play a role in the pathogenesis of postoperative endophthalmitis. Shorter duration of operative manipulation and exposure to contaminating sources may decrease the chances of postoperative endophthalmitis.

Adherence of ocular isolates of staphylococcus epidermidis to ACRYSOF intraocular lenses. A scanning electron microscopy and molecular biology study

PURPOSE

To investigate the adherence of two clinically relevant ocular isolates of Staphylococcus epidermidis to ACRYSOF intraocular lenses (IOLs) (Alcon Surgical, Fort Worth, Texas) and to determine whether the strains under study carried the intercellular adhesion (ica) locus, which encodes production of S. epidermidis antigens mediating adherence to biomaterials.

DESIGN

Experimental study.

PARTICIPANTS

The authors examined the in vitro adherence of two clinically relevant ocular isolates of S. epidermidis (S. epidermidis 1 and S. epidermidis 2). Adherence was tested on six ACRYSOF IOLs.

METHODS

Three IOLs were placed in three separate test tubes containing 5 ml of S. epidermidis 1 suspension, and three other IOLs were placed in three test tubes containing 5 ml of S. epidermidis 2 suspension. At different times (3, 30, and 90 minutes), the IOLs were removed from the test tubes and rinsed in sterile phosphate buffered solution. The lenses were then fixed in glutaraldehyde, postfixed in osmium tetroxide, and serially dehydrated in ethyl alcohol. After critical point drying, they were sputter-coated with gold and then examined with a scanning electron microscope. In addition, polymerase chain reaction amplification was used to investigate whether the isolates under study carried the ica locus.

MAIN OUTCOME MEASURES

The number of adhered bacteria per area (square millimeters) of IOL optic was calculated. Statistical analysis included calculation of arithmetic means and 95% confidence intervals (t test). Polymerase chain reaction amplification products were visualized in ethidium bromide-stained agarose gel.

RESULTS

Direct counting of adherent bacteria in scanning electron microscopy photographs revealed that the total amount of adhered bacteria per area of IOL optic after 3, 30, and 90 minutes of incubation in bacterial suspension was 1306/mm(2), 3389/mm(2), and 7195/mm(2) (S. epidermidis 1) and 778/mm(2), 1056/mm(2), and 3861/mm(2) (S. epidermidis 2). Differences at 30 and 90 minutes were statistically significant (P: = 0.01 and 0.02, respectively). Polymerase chain reaction amplification revealed that S. epidermidis 1 contained the ica locus, whereas S. epidermidis 2 was ica negative.

CONCLUSIONS

Different ocular isolates of S. epidermidis may differ significantly with regard to adherence to ACRYSOF IOLs. Adherence appeared to be greater when the bacterial DNA contained the ica locus. Strains of S. epidermidis carrying the ica locus may play an important role in the pathogenesis of some forms of endophthalmitis occurring after cataract surgery.

In vitro adhesion of Staphylococcus epidermidis to intraocular lenses

PURPOSE

To compare the in vitro adherence of slime-producing and non-slime-producing Staphylococcus epidermidis to different intraocular lenses (IOLs) to study the organism's contribution to postoperative endophthalmitis.

METHODS

Strains of slime-positive (ATCC 35984) and slime-negative (ATCC 12228) S epidermidis were used. The IOLs were made of poly(methyl methacrylate) (PMMA), PMMA with polypropylene haptics, silicone, hydrogel, acrylic, heparin-surface-modified (HSM) PMMA, and fluorine-surface-modified PMMA. The lenses were incubated overnight with bacteria, then sonicated and vortexed to separate the adhered bacteria. Quantitative cultures were performed and the results statistically analyzed.

RESULTS

Slime-negative strains of S epidermidis adhered to all IOLs but at a lower level than slime-positive strains. The most adherent lenses were acrylic with the positive strain and PMMA with the negative strain. The least adherent IOLs were PMMA with the positive strain and hydrogel with the negative strain. There were no significant differences between rigid and foldable lenses. Polypropylene was significantly more adherent than PMMA to the slime-positive strain. The acrylic and the HSM PMMA IOLs were significantly more adherent to the positive strain.

CONCLUSIONS

In vitro, there were significant differences in bacterial adhesion among IOL materials. Slime-positive strains of S epidermidis were more adherent than slime-negative ones.

Vitrectomy for endophthalmitis after intraocular lens implantation

PURPOSE

To report the results of vitrectomy and intraocular lens (IOL) removal for the treatment of endophthalmitis after IOL implantation.

METHODS

We reviewed 14 eyes of 14 patients who underwent pars plana vitrectomy because of postoperative endophthalmitis. Culture results, surgical methods, and visual outcome are presented.

RESULTS

The cultures grew Enterococcus faecalis (n = 3), Staphylococcus epidermidis (n = 2), Propionibacterium acnes (n = 1), and gram-negative bacillus (n = 3). The eyes infected with E. faecalis had poor visual outcome. Eleven eyes treated by the combination of pars plana vitrectomy and IOL removal did not have a recurrence. The remaining 3 eyes on which only vitrectomy was performed had a recurrence, and the additional procedures consisting of vitrectomy and IOL removal could result in eradicating endophthalmitis.

CONCLUSIONS

A higher rate of E. faecalis was detected and these eyes had severe inflammation and poor visual outcome. Combined vitrectomy and IOL removal may be a more certain method to prevent recurrence.

Antibiotics in the irrigating solutions reduce Staphylococcus epidermidis adherence to intraocular lenses

PURPOSE

To investigate the effect of antibiotics in the irrigating solutions on hydrophobicity, slime production and the adherence of Staphylococcus epidermidis to intraocular lenses (IOLs).

METHODS

A standard culture of S. epidermidis was incubated with a control phosphate-buffered saline (PBS) or PBS containing vancomycin (20 micrograms/ml) or gentamicin (8 micrograms/ml) or a combination of gentamicin and vancomycin (8 and 20 micrograms/ml, respectively) for 30, 60 and 120 min at 35 degrees C. The bacteria were harvested by centrifugation, and washed with PBS before incubation with IOLs for 1 h. Adhesion of bacterial cells to IOLs was determined by counting the viable cells attached to the lenses. Slime production on IOLs was measured using safranin staining. Hydrophobicity of the control cultures and cultures treated with antibiotics was assayed on the basis of the hexadecane droplet method.

RESULTS

Bacterial exposure to antibiotics produced a time-dependent significant decrease in bacterial hydrophobicity and adherence to IOLs compared with the untreated control cells (p < 0.001). Hydrophobicity showed a significant correlation with adherence (r = 0.89, p < 0.001). Gentamicin was significantly more effective than vancomycin, and the synergistic combination of gentamicin and vancomycin was the most effective in reducing bacterial adherence to IOLs, hydrophobicity and slime production.

CONCLUSIONS

The use of antibiotics in the irrigating solutions during cataract surgery may be useful in reducing bacterial adherence to IOLs. Further studies are needed to determine the clinical implications of these findings in reducing the incidence of post-operative endophthalmitis associated with IOL implantation.

[In vitro adherence of bacteria to intraocular lenses of different materials]

OBJECTIVE

To compare the in vitro adherence of different bacteria onto the surface of various intraocular lenses (IOLs).

METHOD

Electron microscopic and bacterial culture quantitative methods were used to study the adherence of Staphylococcus (S) epidermidis, Staphylococcus aureus and Pseudomonas (P) aeruginosa onto the surface of PMMA and other three foldable IOL materials (HEMA, ACRY, SI).

RESULTS

S. Epidermidis: HEMA < ACRY < SI < PMMA; S. aureus: HEMA was the least and PMMA was the most, no significant difference between ACRY and SI IOLs; P. aeruginosa: HEMA was the least while no significant difference among PMMA, SI and ACRY IOLs (P > 0.05).

CONCLUSION

The foldable IOLs have the potent ability to reduce the infectious endophthalmitis after surgery of extraction of cataract with IOL implantation.

Reduction of mucoid Staphylococcus epidermidis adherence to intraocular lenses by selected antimicrobial agents

The effect of low concentrations of various antimicrobial agents on the adherence of mucoid Staphylococcus epidermidis to intraocular lenses was investigated. Adherent growth of S. epidermidis on to polymethylmethacrylate lenses was greatly diminished by ciprofloxacin and clindamycin (>75%), followed by ceftazidime ( approximately 50%) and less affected by gentamicin and vancomycin (<25%) compared to the adherent growth of control untreated cells. The reduction in adherence growth was concentration-dependent and found to be due to the inhibition of slime production since no growth inhibition was observed at the concentrations used. Cell surface hydrophobicity was markedly reduced in parallel to the inhibition of adherence as compared to the control cells. The differential effect of antibiotics on adherence, regardless of their antimicrobial activity, may have a clinical significance in reducing the incidence of postoperative endophthalmitis and intraocular inflammation due to the reduction of cell adherence.

The role of intraocular lenses in anterior chamber contamination during cataract surgery

BACKGROUND

Bacterial endophthalmitis is a rare vision-threatening disease, usually caused by microorganisms that are natural inhabitants of the eye lids and conjunctiva. This study was conducted to investigate the role of intraocular lenses (IOLs) in introducing bacterial contamination into the eye during cataract surgery and the efficacy of povidone-iodine solution in prevention this ocular inoculum.

METHODS

Fifty patients underwent routine cataract surgery and intraocular lens implantation. One group of the patients was pretreated with external disinfection using povidone-iodine 4% before surgery, while the other group was only pretreated with saline irrigation. Before IOL implantation, a test IOL was placed on the conjunctiva and taken for microbiological studies. Anterior chamber tap was done at the beginning and at the end of each operation. Positive bacterial growth was followed by bacterial identification and sensitivity tests to various antibiotics.

RESULTS

Bacterial growth was obtained in 14 of the 50 eyes (28%); in 5 eyes the organism was cultured from tapped aqueous and in 9 eyes from the test IOLs. Prophylactic use of povidone-iodine 4% solution effectively reduced the contamination rate from 34.7% to 16.7%. Coagulase-negative staphylococci were the most common organisms isolated (72%). Most organisms were sensitive to vancomycin (86%) and to fucidic acid (71%). There were no cases of clinical endophthalmitis.

CONCLUSIONS

IOLs are apparently potential vehicles for introduction of intraocular bacterial contamination. Instillation of povidone-iodine 4% into the cul-de-sac reduces the risk of bacterial inoculum. Vancomycin is the most effective single agent against intraocular contamination. In order to reduce potential intraocular contamination it is advisable to avoid contact between the IOL and ocular tissues.

Electron microscopy study of explanted intraocular lenses from clinically noninfected eyes

PURPOSE

To determine whether intraocular lenses (IOLs) in clinically noninfected eyes are coated with a significant, bacteria-containing biofilm.

SETTING

The Oxford Eye Hospital, Oxford, United Kingdom.

METHODS

Twenty-six IOLs, removed for reasons other than endophthalmitis from 26 patients attending the Oxford Eye Hospital over a 3 year period, were examined by electron microscopy. Immediately following explantation, the IOL was placed in glutaraldehyde 4% in 0.1 M phosphate buffer solution and processed for scanning electron microscopy (SEM). Areas of interest were reprocessed for transmission electron microscopy (TEM).

RESULTS

There was no evidence of a bacterial biofilm on any IOL. In 5 IOLs, significant host cellular debris was seen at the tip of the haptic or at the optic-haptic junction. In 4 of them, clusters of coccoid-shaped structures were seen at the optic-haptic junction on SEM, but examination by TEM showed these structures to be melanosomes, not bacteria.

CONCLUSION

We found no evidence to suggest that a significant number of IOLs are coated with a bacterial biofilm in clinically noninfected cases. We advocate the use of TEM to distinguish between coccoid bacteria and melanosomes.

Extrusion of an anterior chamber intraocular lens complicated by Haemophilus endophthalmitis

PURPOSE

To describe a case of late postoperative endophthalmitis in a patient who had undergone anterior chamber intraocular lens implantation 6 years previously.

METHOD

Onset, course, and outcome of the patient's eye disease are presented.

RESULTS

The patient was initially examined with erosion of the eyewall, extrusion of the lens haptic, and endophthalmitis. Intraocular cultures disclosed the pathogenic organism to be Haemophilus influenzae.

CONCLUSION

Anterior chamber intraocular lens haptic extrusion can have grave consequences, including endophthalmitis and severe visual loss.

In vitro adherence of Pseudomonas aeruginosa to four intraocular lenses

PURPOSE

To compare the relative degrees of adherence of a clinical strain of Pseudomonas aeruginosa to the optic material of four intraocular lenses (IOLs).

SETTING

Center for Applied and Environmental Microbiology, Georgia State University, Atlanta, Georgia, USA.

METHODS

Intraocular lens optics made of poly(methyl methacrylate) (PMMA), AcrySof-acrylic, and silicone were included in this study. The IOLs were incubated in a minimal medium with cells of P. aeruginosa for 2 hours and 18 hours. Cells in the 2 hour experiment were prelabeled with 3H-leucine; those in the 18 hour experiments were postlabeled. After rinsing the IOLs to remove loosely adherent cells, we determined the number of cells adhered to coded lenses from calibration curves of disintegrations per minute versus cells per square millimeter. Additional lenses were incubated with P. aeruginosa and examined with scanning electron microscopy.

RESULTS

The adherence of P. aeruginosa in order of increasing magnitude was AcrySof-acrylic < PMMA < silicone 1 < silicone 2. The differences between all groups were statistically significant. The scanning electron microscopy observations were in general agreement with the radiolabel studies.

CONCLUSIONS

The AcrySof-acrylic IOL was less susceptible to primary adherence and 18 hour biofilm formation by P. aeruginosa than the PMMA and silicone IOLs, indicating that this material reduced pseudomonad adherence and the risk of endophthalmitis following cataract surgery.

[Adherence of staphylococci of different hydrophobicity. Study of various intraocular lenses]

BACKGROUND

A major goal in research on intraocular lenses (IOL) is the development of new polymers and modifications to reduce foreign-body reactions after implantation. This effect may be achieved by a reduction in the surface hydrophobicity of the polymers. To illustrate the influence of surface modifications on bacterial adhesiveness, the most often isolated organism in "low-grade" postoperative endophthalmitis, Staphylococcus epidermidis, was used.

MATERIALS AND METHODS

For this reason three strains of this species, the type strain ATCC 14990 and two clinical isolates (8687, 6579 I) with different hydrophobic surface properties were studied. IOL, used in the experiments were either made of PMMA or silicone with modified surfaces (unpolished, polished, heparinized). The adhesiveness of H3-thymidin-labeled bacteria was calculated/mm2 of lens surface. Each experiment was performed in triplicate and repeated three times.

RESULTS

The hydrophobic-type strain showed stronger adherence to unpolished PMMA surface (8000 bacteria per mm2) compared to the polished (5200 bacteria/mm2). In contrast, the hydrophilic strain adhered with 2000 bacteria/mm2 to the unpolished and with 4200 bacteria/mm2 to the polished surface. Polishing PMMA lenses diminished the differences between the three strains. However, surface passivation of silicone lenses increased the adhesion rate of the hydrophilic strain up to 9600 bacteria/mm2. Treatment of PMMA lenses with heparin increased the adhesiveness of the hydrophilic strain and reduced the adhesion rate of the hydrophobic type strain to 250 bacteria/mm2.

CONCLUSIONS

It was demonstrated that bacterial adherence to IOL also involves hydrophobic interactions. Obviously, however, that adherence reflects a complex of interactions between the two surfaces.