Ocular Isolates Research Articles

Pseudomonas aeruginosa with lasI quorum-sensing deficiency during corneal infection.

To understand the importance of Pseudomonas aeruginosa quorum-sensing systems in the development of corneal infection, the genotypic characteristics and pathogenesis of seven ocular isolates with low-protease and acyl homoserine lactone (AHL) activity and quorum-sensing mutants of PAO1 deficient in lasI, lasR, or rhlR were investigated in the study. The possession of the quorum-sensing genes lasI, lasR, rhlI, rhlR, and the quorum-sensing controlled genes lasB, aprA, and rhlAB in the clinical isolates were determined by polymerase chain reaction and Southern blot hybridization. Elastinolytic activity, controlled by the las system, was assayed using elastin Congo red and rhamnolipid production controlled by the rhl system was assessed using agar plates containing methylene blue/cetyltrimethyl ammonium bromide. Induction of keratitis was examined in a scarified inbred BALB/c mouse model. The clinical isolates Paer1 and -3 were lasI and lasR negative, and the isolates Paer2 and -4 were rhlR and rhlAB negative. The isolates Paer17, Paer26, 6294 and 6206 possessed all the genes examined. There was no rhamnolipid production in clinical isolates Paer2 and -4. The isolates Paer1 and -3 were virtually avirulent in the scarified mouse corneas. Using isogenic PAO1 mutants, strain lasI showed a markedly reduced virulence in the corneal infection model. The remainder of the clinical isolates and the lasR or rhlR mutant strains caused severe keratitis. These results indicate that quorum-sensing deficiency may occur naturally in clinical isolates, and the possession of lasI and hence a functional Las quorum-sensing system may be important in development of corneal infection.

In vitro investigation of voriconazole susceptibility for keratitis and endophthalmitis fungal pathogens

Purpose To update the spectrum of ocular fungal isolates and investigate the in vitro efficacy of voriconazole and other antifungals. Design Experimental study. Methods Microbiology database was scanned and fungal isolates associated with keratitis (419) and endophthalmitis (122) were analyzed for classification and isolate frequency. The Sensititre YeastOne microdilution antifungal susceptibility test was used to evaluate susceptibility (MICs) of 34 common fungal pathogens against amphotericin B, fluconazole, ketoconazole, 5-flucytosine, itraconazole, and voriconazole. Ten of the test isolates were sent to a reference laboratory to validate the Sensititre results. Results Fusarium species remains the most frequent corneal fungal pathogen (60.1%). Colletotrichum species (4.1%) has emerged as the fifth most common mold in keratitis. Top yeast isolates from cornea included Candida albicans (52.3%) and Candida parapsilosis (37.3%). Half of the intraocular pathogens were Candida species. Paecilomyces (2.9%) and Philophora (1.9) were unusual pathogens. In vitro susceptibility profiles were voriconazole (100%), ketoconazole (82.4%), amphotericin (76.5%), itraconazole (67%), fluconazole (60%), and 5-FC (60%). Voriconazole MIC 90 were lowest for Candida species (0.016 μg/ml) and highest for Fusarium species (2 μg/ml). Reference laboratory MICs correlated 100% for yeast isolates (0.016 μg/ml) but were fourfold higher for Fusarium species (8 μg/ml). MIC 90 for Aspergillus species was 0.5 μg/ml. Conclusions Candida, Fusarium, and Aspergillus species remain frequent fungal pathogens. Voriconazole may have a role in the therapeutic management of Candida and Aspergillus ocular infections. Clinical efficacy must determine the role for other fungal pathogens. Human use and animal models will determine its use in the clinical setting.

Fluoroquinolone resistance in ophthalmology and the potential role for newer ophthalmic fluoroquinolones

The three topical ophthalmic fluoroquinolones recently introduced into the U.S. market—levofloxacin, gatifloxacin, and moxifloxacin—offer several advantages over the previously available fluoroquinolones (norfloxacin 0.3%, ciprofloxacin 0.3%, and ofloxacin 0.3%). These include enhanced spectrum and potency for Gram-positive cocci and possibly atypical mycobacterial species, improved penetration into the anterior segment, and reduced propensity to promote the development of resistance. Although published data and clinical experience with these agents is quite limited given their relatively recent entry into the U.S. market, this perspective will attempt to provide an understanding of the potential role of these newer fluorquinolones in addressing the problem of increasing fluoroquinolone resistance amongst bacterial ocular isolates.

Folding procedure for acrylic intraocular lenses

Purpose: To compare in vitro the effect of 2 standard methods of folding acrylic intraocular lenses (IOLs) on surface characteristics and bacterial adhesion. Setting: Eye Clinic and Department of Health—Microbiology Unit, University of Florence, Florence, Italy. Methods: To evaluate the effect of folding, 2 types of acrylic IOLs were not folded or folded with a forceps or an injector and then processed for scanning electron microscopy (SEM) examination. Bacterial adhesion was assessed using an ocular isolate of Pseudomonas aeruginosa. Nonfolded and folded IOLs were placed in test tubes containing the bacterial suspension for direct counting of viable adherent bacteria and for SEM. Results: The injector-folded IOLs did not show major alterations on the surface; 5 of the 9 forceps-folded IOLs showed marks or scratches in the profile of the optic. The mean number of viable adherent bacteria per area of IOL optic was 1082 (95% confidence interval [CI], 835-1330) in forceps-folded IOLs, 366 (95% CI, 192-359) in injector-folded IOLs, and 206 (95% CI, 123-289) in nonfolded IOLs. Scanning electron microscopy confirmed more surface irregularities on forceps-folded IOLs, with bacteria adherent preferentially on the surface scratches. Conclusion: Forceps-folding provoked more surface irregularities, which probably make IOLs more susceptible to bacterial adhesion.

Induction of cytokines from polymorphonuclear leukocytes and epithelial cells by ocular isolates of Serratia marcescens

Purpose: During contact lens wear, bacterial contamination of the lens can lead to the development of microbial keratitis (MK) or contact lens induced acute red eye (CLARE). Inflammatory mediators released by the host may heighten the response. We have examined the ability of human corneal epithelial cells and polymorphonuclear leukocytes (PMNs) to release cytokines upon stimulation with bacteria. Methods: Serratia marcescens strains were added to corneal epithelial cells or PMNs. After incubations of up to 20 hours, supernatants were assayed for the presence of inflammatory mediators by ELISA. Results: All strains stimulated PMNs to release IL-8 and LTB4. Epithelial cells did not release LTB4. IL-8 was released after exposure to most S. marcescens isolates. A sub-group of strains stimulated the release of TNF-α from corneal epithelial cells. Conclusions: S. marcescens can stimulate the release of inflammatory mediators from both PMNs and corneal epithelial cells. This release could be important in the progression and resolution of MK and CLARE.

Shifting trends in in vitro antibiotic susceptibilities for common ocular isolates during a period of 15 years

Purpose To assess the in vitro susceptibility of the most common ocular bacterial isolates to several antibiotics and verify changing trends in the antibiotic susceptibility in a 15-year period. Design Experimental study. Methods All cultures positive for Staphylococcus aureus, coagulase-negative Staphylococcus (CNS), Streptococcus sp, and Pseudomonas sp in conjunctival (n = 4,585) and corneal (n = 3,779) samples from patients seen at the Federal University of São Paulo from 1985 to 2000 were evaluated. Cultures were performed in liquid and solid media, and susceptibility tests were done to amikacin, gentamicin, neomycin, tobramycin, ciprofloxacin, norfloxacin, ofloxacin, cephalothin, and chloramphenicol. Results Amikacin and neomycin showed an improvement of their sensitivity during the study period (88%–95% and 50%–85%, respectively) for corneal and conjunctival samples. Gentamicin and tobramycin revealed a decrease of sensitivity in time, from 95% to less than 80% in corneal and conjunctival samples. Ciprofloxacin, norfloxacin, and ofloxacin had good sensitivity to all evaluated bacteria, better in conjunctiva (95%) than in cornea (90%). Sensitivity of S. aureus to cephalothin decreased during the study but was still 98% for CNS. Chloramphenicol had good sensitivity to S. aureus (85% in corneal and 92%in conjunctival samples), CNS (87% and 88.5%), and Streptococcus sp (95% and 96%). Conclusions Gentamicin, tobramycin, and cephalothin decreased their in vitro susceptibility to all tested pathogens. The fluoroquinolones remained a good choice in the treatment of ocular infections, with high suscep-tibility to all pathogens tested. Chloramphenicol also revealed an increase in its susceptibility to all bacteria evaluated.

Polymorphisms in Chlamydia trachomatis tryptophan synthase genes differentiate between genital and ocular isolates.

We previously reported that laboratory reference strains of Chlamydia trachomatis differing in infection organotropism correlated with inactivating mutations in the pathogen's tryptophan synthase (trpBA) genes. Here, we have applied functional genomics to extend this work and find that the paradigm established for reference serovars also applies to clinical isolates - specifically, all ocular trachoma isolates tested have inactivating mutations in the synthase, whereas all genital isolates encode a functional enzyme. Moreover, functional enzyme activity was directly correlated to IFN-gamma resistance through an indole rescue mechanism. Hence, a strong selective pressure exists for genital strains to maintain a functional synthase capable of using indole for tryptophan biosynthesis. The fact that ocular serovars (serovar B) isolated from the genital tract were found to possess a functional synthase provided further persuasive evidence of this association. These results argue that there is an important host-parasite relationship between chlamydial genital strains and the human host that determines organotropism of infection and the pathophysiology of disease. We speculate that this relationship involves the production of indole by components of the vaginal microbial flora, allowing chlamydiae to escape IFN-gamma-mediated eradication and thus establish persistent infection.

Polymorphisms in Chlamydia trachomatis tryptophan synthase genes differentiate between genital and ocular isolates

Polymorphisms in Chlamydia trachomatis tryptophan synthase genes differentiate between genital and ocular isolates

Analysis of the herpes simplex virus type 1 UL6 gene in patients with stromal keratitis

Recent work suggests that herpes simplex virus (HSV) stromal keratitis in the mouse is caused by autoreactive T lymphocytes triggered by a 16 amino acid region of the HSV UL6 protein (aa299–314) (Z.-S. Zhao, F. Granucci, L. Yeh, P. Schaffer, H. Cantor, 1998, Science 279, 1344–1347). In the present study we sought to determine whether genetic variation of this presumed autoreactive UL6 epitope is responsible for different pathogenic patterns of human HSV keratitis. To accomplish this, we sequenced the HSV UL6 gene from ocular isolates of 10 patients with necrotizing stromal keratitis, 7 patients with recurrent epithelial keratitis, and 8 patients with other forms of HSV keratitis. The sequences obtained predicted identical UL6(299–314) epitopes for all 25 viral isolates. Furthermore, the upstream sequence of all isolates was free of insertions, deletions, and stop codons. We conclude that different pathogenic patterns of human HSV keratitis occur independent of genetic variation of the HSV UL6 (299–314) epitope.

Pseudomonas aeruginosa Strains with Lipopolysaccharide Defects Exhibit Reduced Intracellular Viability after Invasion of Corneal Epithelial Cells

Pseudomonas aeruginosa is a leading cause of infectious keratitis. Many ocular isolates of this bacterium invade corneal epithelial cells in vitro and in vivo. Antibiotic survival assays have shown that a complete core lipopolysaccharide is required for full epithelial invasion by P. aeruginosa. In this study, we show that P. aeruginosa mutants with defects in their lipopolysaccharide core and O antigen exhibited reduced viability after internalization by corneal epithelial cells. Restoration of lipopolysaccharide core and O antigen expression by complementation with the plasmid pLPS1 restored intracellular survival. P. aeruginosa strains with a complete lipopolysaccharide survived and replicated within the cells. The data suggest that lipopolysaccharide is involved in the intracellular survival and/or replication of P. aeruginosa, indicating an additional mechanism by which this important virulence factor may contribute to the pathogenesis of corneal infection.

In vitro Activity of Sagamicin against Ocular Bacterial Isolates

The in vitro antibacterial activity of sagamicin, gentamicin, tobramycin and norfloxacin was evaluated against 180 recent clinical isolates obtained from patients with ocular infections. Good activity was demonstrated for the 3 aminoglycosides against methicillin-sensitive Staphylococcus aureus and Staphylococcus epidermidis. All 4 compounds showed a lower activity against methicillin-resistant staphylococci. Sagamicin was highly effective against enterobacteriaceae with a MIC₉₀ of 2 mg/l and presented good antipseudomonal activity similar to that of gentamicin. Intraocular lenses impregnated with a sagamicin solution showed a good antistaphylococcal activity immediately after preparation. In our strain collection, the ability to produce slime was more frequent among methicillin-resistant S. epidermidis strains than methicillin-sensitive S. epidermidis (85 versus 70%). The attachment of 2 S. epidermidis strains to plastic surfaces was partially prevented by sagamicin subinhibitory concentrations. On the contrary, sub-MIC levels of norfloxacin increased the adhesion of S. epidermidis.

The disinfection of contact lenses contaminated with adenovirus

PURPOSE: We compared the efficacy of different contact lens disinfection systems to eliminate adenovirus. METHODS: Laboratory study evaluating the elimination of adenoviral ocular isolates by contact lens disinfection systems. Hard (gas permeable) and soft contact lenses were contaminated with adenovirus serotypes 8 and 19, and then they were disinfected with chemical, hydrogen peroxide, and heat sterilization systems. The survival of the adenovirus was determined by the shell vial technique. RESULTS: Adenovirus survived chemical and hydrogen peroxide disinfection but not heat sterilization. CONCLUSION: Because heat sterilization is not readily available to sterilize adenovirus contaminated contact lenses, it may be prudent for patients with adenoviral keratoconjunctivitis to dispose of unclean contact lenses.

Adhesion of Pseudomonas aeruginosa ocular isolates to mucin

The purpose of this study was to compare the adhesion of Pseudomonas aeruginosa ocular isolates to mucin. An adhesion assay was developed using biotin-labelled P. aeruginosa strains (two corneal ulcer, two acute red eye, one asymptomatic and one standard strains) incubated with porcine gastric mucin immobilized on a nitrocellulose membrane. The adhesion was semiquantified using densitometry. The results showed that all P. aeruginosa strains tested were able to adhere to mucin to various extents with three strains (one corneal ulcer one acute red eye, one asymptomatic) binding signifcantly greater than the negative control (P < 0.1). Results suggest that ocular strains of P. aeruginosa strains differ in their adhesion to mucin but this did not correlate with the pathogenic origin of the strain. It is concluded that the adhesion of P. aeruginosa strains to mucin alone may not be a principal determinant of pathogenesis but may be a contributing factor along with other bacterial virulence traits.

Survival ofSerratia marcescensin the Presence of Complement

Serratia marcescens has been isolated from a variety of ocular infections and/or infammation. In order to survive in the eye, strains must be able to resist host defence systems. Complement has been shown to have an increased concentration and to be active during sleep. Not only is the complement system involved in host defence, but its activation can also produce in ammation. The aim of the present study was to examine the ability of ocular isolates of S. marcescens to withstand complement attack, activate complement and to examine the mechanisms used for evasion of this host defence system. The majority of isolates tested (4/6) were resistant to complement attack. These isolates were able to activate both complement pathways, as detected by enzyme-linked immunosorbent assays (ELISA) and western blotting assays. Components detected included C4, Factor B, C3 and C5. Possible mechanisms of resistance were elucidated including quantity of lipopolysaccharide (LPS) on the cell surface, ability to bind lactoferrin, types of complement components deposited onto the surfaces of strains, and the amount and location of C3 bound on the surface, as determined by transmission electron microscopy. Complement-resistant strains generated iC3b, bound more lactoferrin (1.7 ± 0.6 for resistant cells compared with 0.4 ± 0.2 for complement-sensitive cells, relative values), and had larger amounts of extractable endotoxin (216.8 ± 88.8 µ g/ml for resistant strains and 36.0 ± 48.4 µ g/ml for sensitive strains). Although there was no direct correlation between the ability to resist and activate complement and the isolation of strains from symptomatic or asymptomatic eyes, the resistance of strains to complement may allow these strains to remain in the eye and the activation of complement may contribute to the in ammatory response seen during infection or ocular infammation. Keywords: Serratia marcescens , complement, host defence, tear ?film.

In vitro Susceptibilities to Topical Antibiotics of Bacteria Isolated from the Surface of Clinically Symptomatic Eyes

Background: The permanent change of resistance patterns of bacteria causing ocular infections makes repeat susceptibility testings against the most recent clinical isolates mandatory. The aim of the present study was to assess the in vitro susceptibility of ocular bacterial isolates of clinically symptomatic eyes admitted to the outpatient clinic of the eye department of a large central hospital to commonly used topical antibiotics. Methods: Ocular isolates (n = 454) were tested for their susceptibility to ofloxacin, ciprofloxacin, norfloxacin, gentamicin, tobramycin, meomycin, bacitracin, erythromycin, tetracycline and chloramphenicol. Results: All three tested fluoroquinolones were found to be very effective against gram-negative organisms but demonstrated some weakness against certain strains of gram-positive germs, in particular coagulase-negative staphylococci and Streptococcus viridans. These germs, however, were very susceptible to bacitracin and chloramphenicol. The relative overall in vitro efficacy was (in decreasing order): chloramphenicol, ciprofloxacin, ofloxacin, norfloxacin, bacitracin, tetracycline, neomycin, erythromycin, tobramycin and gentamicin. Conclusion: Chloramphenicol had the highest overall in vitro efficacy, but has potential lethal side effects. The fluoroquinolones were highly effective, especially being superior to the aminoglycosides tested, but no single antibiotic provided 100% coverage against all of the bacterial isolates that were tested.

Genetic analyses of Acanthamoeba isolates from contact lens storage cases of students in Seoul, Korea.

We conducted both the small subunit ribosomal DNA (SSU rDNA) polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and mitochondrial (mt) DNA RFLP analyses for a genetic characterization of Acanthamoeba isolates from contact lens storage cases of students in Seoul, Korea. Twenty-three strains of Acanthamoeba from the American Type Culture Collection and twelve clinical isolates from Korean patients were used as reference strains. Thirty-nine isolates from contact lens storage cases were classified into seven types (KA/LS1, KA/LS2, KA/LS4, KA/LS5, KA/LS7, KA/LS18, KA/LS31). Four types (KA/LS1, KA/LS2, KA/LS5, KA/LS18) including 33 isolates were regarded as A. castellanii complex by riboprints. KA/LS1 type was the most predominant (51.3%) in the present survey area, followed by KA/LS2 (20.9%), and KA/LS5 (7.7%) types. Amoebae of KA/LS1 type had the same mtDNA RFLP and riboprint patterns as KA/E2 and KA/E12 strains, clinical isolates from Korean keratitis patients. Amoebae of KA/LS2 type had the identical mtDNA RFLP patterns with A. castellanii Ma strain, a corneal isolate from an American patient as amoebae of KA/LS5 type, with KA/E3 and KA/E8 strains from other Korean keratitis patients. Amoebae of KA/LS18 type had identical patterns with JAC/E1, an ocular isolate from a Japanese patient. Three types, which remain unidentified at species level, were not corresponded with any clinical isolate in their mtDNA RFLP and riboprint patterns. Out of 39 isolates analyzed in this study, mtDNA RFLP and riboprint patterns of 33 isolates (84.6%) were identical to already known clinical isolates, and therefore, they may be regarded as potentially keratopathogenic. These results suggest that contact lens wearers in Seoul should pay more attention to hygienic maintenance of contact lens storage cases for the prevention of Acanthamoeba keratitis.

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.

Rapid identification of Pseudomonas aeruginosa from ocular isolates by PCR using exotoxin A-specific primers

The purpose of this research was to evaluate the use of PCR for the identification of ocular isolates ofPseudomonas aeruginosa by using primers specific to the exotoxin A gene of the bacteria. Genomic DNA was obtained from ocular microbial isolates of keratitis patients. Primers were designed based on the published sequence of the exotoxin A gene ofP. aeruginosa . Using the primers designed, PCR reactions were performed on the DNA samples. The PCR was also examined for its specificity and sensitivity. In addition, a direct PCR using heating method was attempted on P. aeruginosa with no separate DNA extraction step. ATCC strains of P. aeruginosa were included as positive controls. The rest of the bacteria other than P. aeruginosa served as negative controls. A single band was obtained when analysed on agarose gel electrophoresis only from samples that contained genomic DNA of P. aeruginosa. The direct PCR method was also successful with the same band produced from the amplification. The whole process was completed within 4 h. The direct PCR amplification targeting at the exotoxin A gene of P. aeruginosa is potentially a rapid, specific, sensitive and relatively simple method for the identification of ocular isolates of P. aeruginosa.

In vitro adherence of staphylococcus epidermidis to polymethyl methacrylate and acrysof intraocular lenses

Purpose To investigate the adherence of one clinically relevant ocular isolate of Staphylococcus epidermidis to polymethyl methacrylate (PMMA) and Acrysof (Alcon Surgical, Fort Worth, TX) intraocular lenses (IOLs). Design Experimental study. Participants The authors examined the in vitro adherence of one clinically relevant ocular isolate of S. epidermidis. Adherence was tested on 12 PMMA IOLs and 12 Acrysof IOLs. Methods Six IOLs (three of each type) were placed in different test tubes containing bacterial suspension (10 8 cfu/ml) and incubated at 37°C. At different times (3 minutes, 30 minutes, and 90 minutes), each IOL type was removed from the test tube, rinsed in sterile phosphate-buffered saline, and transferred into sterile brain-heart infusion broth. The broth with the IOL was sonicated on low power for 3 minutes to remove adhered bacteria. Two serial 10-fold dilutions of the broth containing the dislodged bacteria were plated on mannitol agar plates. The plates were incubated overnight at 37°C and then bacterial colonies were counted. All assays were performed in triplicate. Additional lenses (three of each type) were incubated with S. epidermidis for different times (3 minutes, 30 minutes, and 90 minutes) and then examined with scanning electron microscopy. Main outcome measures The number of adhered bacteria per area (mm 2) of IOL optic was calculated. Statistical analysis included calculation of arithmetic means and 95% confidence intervals ( t test). Results Direct counting of viable adherent bacteria released by sonication showed that the amount of adhered bacteria per area of IOL optic after 3, 30, and 90 minutes’ incubation in S. epidermidis suspension was 0.1 × 10 2/mm 2, 3.6 × 10 2/mm 2, and 11 x 10 2/mm 2 (PMMA IOLs), and 4.4 × 10 2/mm 2, 3.1 × 10 2/mm 2, and 2.3 × 10 2/mm 2 (Acrysof IOLs). 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’ incubation in S. epidermidis suspension was 1.1 × 10 2/mm 2, 4.4 × 10 2/mm 2, and 5.5 × 10 2/mm 2 (PMMA IOLs) and 13 × 10 2/mm 2, 33.9 × 10 2/mm 2, and 72 × 10 2/mm 2 (Acrysof IOLs). Conclusions Results suggest that in vitro adherence of S. epidermidis to IOLs is influenced by IOL materials. After 3 minutes’ incubation, Acrysof IOLs appeared to be more permissive to S. epidermidis adherence than PMMA IOLs. The difference was statistically significant ( P < 0.05). However, at 90 minutes, Acrysof IOLs had a lower viable bacterial count than did the PMMA IOLs. Bacterial adherence appeared to be greater in areas with surface irregularities. Adherence of S. epidermidis to IOLs may play a role in the pathogenesis of some forms of endophthalmitis after cataract surgery.

Alterations in ocular pathogen susceptibility to gentamicin and tobramycin

Purpose: To evaluate and compare the "in vitro" susceptibility of ocular bacterial isolates to aminoglycoside antibiotics (gentamicin and tobramycin) and to analyze the alteration in susceptibility after 14 years of introduction of tobramycin in Brazilian ophthalmic practice. Methods: The results of antibiotic susceptibility tests in a period of three years with 887 bacterial strains (Study "A") were retrospectively analyzed and then compared with the results obtained fourteen years ago with 124 microorganisms (Study "B"), when tobramycin was first tested in Brazil for isolated eye strains. In both studies, the data analyzed were from the files of the Ocular Microbiology Laboratory of the Federal University of São Paulo. Results: The "in vitro" effectiveness of both antibiotics regarding the total number of positive isolates was significantly higher for tobramycin in both studies. An increase in the Staphylococcus aureus strains resistant to tobramycin and only a decreasing trend in the number of microorganisms resistant to gentamicin was observed. With Pseudomonas sp, a strong tendency to the increase of susceptibility to gentamicin and to the appearance of strains resistant to tobramycin occurred. Conclusions: The introduction of tobramycin in the treatment of ocular infections and the possible decrease in number of gentamicin prescriptions during the last fourteen years might be the cause of modifications in the susceptibility observed in the total of positive isolates mainly Staphylococcus aureus and Pseudomonas sp. For the isolated microorganisms from the conjunctiva, the sensitivity to both antibiotics was equivalent.