Biofilm formation and coccal organisms in infectious crystalline keratopathy

Infectious crystalline keratopathy following Descemet's stripping automated endothelial keratoplasty

INTRODUCTION

We describe this first case of Staphylococcus epidermidis causing infectious crystalline keratopathy (ICK) following Descemet stripping endothelial keratoplasty (DSAEK), that resolved after 5 weeks of topical antibiotic and corticosteroid treatment.

CASE DESCRIPTION

An 80-year-old woman presented with blurred vision, redness, and ocular pain 9 months after successful DSAEK. Slit lamp examination revealed the presence of white, non-suppurative, deep-branching stromal infiltrates, and a clinical diagnosis of ICK was made. Cultures of corneal scapings isolated multidrug-resistant Staphylococcus epidermidis. No subsequent surgical procedures were performed. Based on antibiotic sensitivity analysis, she was treated successfully with topical vancomycin and chloramphenicol for 5 weeks. Complete resolution of the infection with minor anterior stromal corneal scarring of the host cornea was noted after 5 weeks of treatment. This case report describes the diagnosis and management of ICK after DSAEK and reviews the relevant literature regarding the occurrence of ICK after DSAEK.

CONCLUSION

In this case, vancomycin and chloramphenicol allowed for the uncomplicated resolution of infection with only minor visual impairment from baseline.

Atypical microbial keratitis

Atypical microbial keratitis refers to corneal infections caused by micro-organisms not commonly encountered in clinical practice. Unlike infections caused by common bacteria, cases of atypical microbial keratitis are often associated with worse clinical outcomes and visual prognosis. This is due to the challenges in the identification of causative organisms with standard diagnostic techniques, resulting in delays in the initiation of appropriate therapies. Furthermore, due to the comparatively lower incidence of atypical microbial keratitis, there is limited literature on effective management strategies for some of these difficult to manage corneal infections. This review highlights the current management and available evidence of atypical microbial keratitis, focusing on atypical mycobacteria keratitis, nocardia keratitis, achromobacter keratitis, and pythium keratitis. It will also describe the management of two uncommonly encountered conditions, infectious crystalline keratopathy and post-refractive infectious keratitis. This review can be used as a guide for clinicians managing patients with such challenging corneal infections.

Paradox of complex diversity: Challenges in the diagnosis and management of bacterial keratitis

Bacterial keratitis continues to be one of the leading causes of corneal blindness in the developed as well as the developing world, despite swift progress since the dawn of the "anti-biotic era". Although, we are expeditiously developing our understanding about the different causative organisms and associated pathology leading to keratitis, extensive gaps in knowledge continue to dampen the efforts for early and accurate diagnosis, and management in these patients, resulting in poor clinical outcomes. The ability of the causative bacteria to subdue the therapeutic challenge stems from their large genome encoding complex regulatory networks, variety of unique virulence factors, and rapid secretion of tissue damaging proteases and toxins. In this review article, we have provided an overview of the established classical diagnostic techniques and therapeutics for keratitis caused by various bacteria. We have extensively reported our recent in-roads through novel tools for accurate diagnosis of mono- and poly-bacterial corneal infections. Furthermore, we outlined the recent progress by our group and others in understanding the sub-cellular genomic changes that lead to antibiotic resistance in these organisms. Finally, we discussed in detail, the novel therapies and drug delivery systems in development for the efficacious management of bacterial keratitis.

Biofilm-Forming Potential of Ocular Fluid Staphylococcus aureus and Staphylococcus epidermidis on Ex Vivo Human Corneas from Attachment to Dispersal Phase

The biofilm-forming potential of Staphylococcus aureus and Staphylococcus epidermidis, isolated from patients with Endophthalmitis, was monitored using glass cover slips and cadaveric corneas as substrata. Both the ocular fluid isolates exhibited biofilm-forming potential by the Congo red agar, Crystal violet and 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-(phenylamino) carbonyl-2H-tetra-zolium hydroxide (XTT) methods. Confocal microscopy demonstrated that the thickness of the biofilm increased from 4–120 h of biofilm formation. Scanning electron microscopic studies indicated that the biofilms grown on cover slips and ex vivo corneas of both the isolates go through an adhesion phase at 4 h followed by multilayer clumping of cells with intercellular connections and copious amounts of extracellular polymeric substance. Clumps subsequently formed columns and eventually single cells were visible indicative of dispersal phase. Biofilm formation was more rapid when the cornea was used as a substratum. In the biofilms grown on corneas, clumping of cells, formation of 3D structures and final appearance of single cells indicative of dispersal phase occurred by 48 h compared to 96–120 h when biofilms were grown on cover slips. In the biofilm phase, both were several-fold more resistant to antibiotics compared to planktonic cells. This is the first study on biofilm forming potential of ocular fluid S. aureus and S. epidermidis on cadaveric cornea, from attachment to dispersal phase of biofilm formation.

Infectious crystalline keratopathy

Infectious crystalline keratopathy was first reported by Gorovoy and colleagues in 1983 when they identified bacteria colonizing a cornea after a penetrating keratoplasty. Subsequent cases have elaborated on the organisms responsible and the management outcomes. Patients present with a white or gray branching opacity originating from an epithelial defect, commonly after a penetrating keratoplasty. Local immunosuppression contributes to the quiescent nature and the limited inflammatory response associated with infectious crystalline keratopathy. Diagnosis of the infective pathogens may be difficult, with a corneal scraping often being too superficial to obtain an adequate specimen. A biofilm is present that advantages microorganism survival, reduces antibiotic bioavailability, and inhibits diagnostic microbial detection. Treatment begins with topical antimicrobials, initially broad spectrum and then targeted to microorganism sensitivity. Adjunctive therapies to enhance the efficacy of treatment include disruption of the microorganism biofilm by laser, intrastromal antibiotics, and keratectomy. In recalcitrant cases, or where corneal scarring ensues, corneal transplantation is required.

Biofilms in infections of the eye

The ability to form biofilms in a variety of environments is a common trait of bacteria, and may represent one of the earliest defenses against predation. Biofilms are multicellular communities usually held together by a polymeric matrix, ranging from capsular material to cell lysate. In a structure that imposes diffusion limits, environmental microgradients arise to which individual bacteria adapt their physiologies, resulting in the gamut of physiological diversity. Additionally, the proximity of cells within the biofilm creates the opportunity for coordinated behaviors through cell–cell communication using diffusible signals, the most well documented being quorum sensing. Biofilms form on abiotic or biotic surfaces, and because of that are associated with a large proportion of human infections. Biofilm formation imposes a limitation on the uses and design of ocular devices, such as intraocular lenses, posterior contact lenses, scleral buckles, conjunctival plugs, lacrimal intubation devices and orbital implants. In the absence of abiotic materials, biofilms have been observed on the capsule, and in the corneal stroma. As the evidence for the involvement of microbial biofilms in many ocular infections has become compelling, developing new strategies to prevent their formation or to eradicate them at the site of infection, has become a priority.

Topical linezolid 0.2% for the treatment of vancomycin-resistant or vancomycin-intolerant gram-positive bacterial keratitis

PURPOSE

To report the successful use of topical linezolid 0.2% in the treatment of gram-positive bacterial keratitis.

STUDY DESIGN

Retrospective, interventional case series.

METHODS

All cases of bacterial keratitis treated at the University of Illinois Eye and Ear Infirmary with topical linezolid were identified from the Cornea and External Disease Clinic and were reviewed for culture results, prior therapy, clinical course, and visual outcome.

RESULTS

Three patients received topical linezolid, all for cases of culture-positive or presumed gram-positive keratitis. Cases consisted of 1 patient with recalcitrant vancomycin-resistant Enterococcus faecalis (VRE) and 2 patients with infectious crystalline keratitis, 1 previously culture-positive for an uncharacterized Staphylococcus and the other for Streptococcus mitis. All 3 patients had rapid resolution of their infectious keratitis and noted no pain or discomfort attributed to the topical therapy. The patient with VRE keratitis developed a consecutive Candida keratitis elsewhere in the same cornea at the end of therapy for her VRE keratitis.

CONCLUSION

Topical linezolid 0.2% can be an effective ophthalmic antibiotic for the treatment of gram-positive keratitis, including VRE, and is both significantly more comfortable and less immediately toxic to the ocular surface than topical vancomycin.

Laser corneal biofilm disruption for infectious crystalline keratopathy

Crystalline keratopathy can be successfully treated by the Nd:YAG laser. We present two cases of crystalline keratopathy managed this way. A 36-year-old female contact lens wearer presented with crystalline keratopathy following recent treatment with topical steroids and antibiotics for a corneal abscess. In this case crystalline keratopathy developed despite the intensive topical antibiotic treatment. A 55-year-old man with a history of acne rosacea, chronic myelomonocytic leukaemia, asthma and Crohn's disease presented with crystalline keratopathy following an episode of infectious keratitis. Treatment with the Nd:YAG laser to the area of involvement was instituted in both cases. Noticeable resolution occurred within days, with subsequent full recovery. No side-effects from the use of the Nd:YAG laser were noted. There have been only two cases previously reported using this treatment modality.

Infectious Crystalline Keratopathy Caused by Gemella haemolysans

PURPOSE

To report a novel case of infectious crystalline keratopathy after penetrating keratoplasty caused by Gemella haemolysans.

METHODS

Observational case report. Patient notes and literature review.

RESULTS

A 51-year-old woman presented with the clinical picture of infectious crystalline keratopathy 18 months after a second penetrating keratoplasty was performed for corneal decompensation secondary to recurrent herpes simplex infection. Corneal biopsy yielded a heavy growth of G. haemolysans. Initial treatment was made up of frequent topical vancomycin 0.5% and was later changed to topical cefuroxime 5% and ofloxacin 0.3%. Snellen visual acuity after complete resolution of the keratitis was 6/60 as a result of a residual corneal scar.

CONCLUSIONS

Gemella haemolysans may be an etiologic agent in infectious crystalline keratopathy. A corneal biopsy may be diagnostic but may also promote healing by allowing direct access of antibiotics to deep-seated infected tissue and by altering the growth environment of the organism.

Bacterial biofilms within the clinical setting: what healthcare professionals should know

Bacterial biofilm formation is the prevailing microbial lifestyle in natural and manmade environments and occurs on all surface types. Biofilm formation develops in several phases and is influenced by various parameters, both environmental and inherent to the attaching cell. Biofilms also serve as protective niches for particular pathogens when outside a host. Although it is accepted that biofilms are ubiquitous in nature, the significance of biofilms in clinical settings, especially with regard to their role in medical-related infections, is often underestimated. It has been found that several aspects of human pathogenesis within a clinical context are directly related to biofilm development. Various types of surfaces in clinical settings are prone to biofilm development and an increased risk of disease may be a direct consequence of their formation. This review describes the process of biofilm formation, highlights the importance of bacterial associations with surfaces in clinical settings and describes various methods for biofilm visualization and control.

Case of a large, movable bacterial concretion with biofilm formation on the ocular surface

OBJECTIVE

To report a case with a large movable bacterial concretion formed on the ocular surface without biomaterials.

METHODS

Interventional case report. A 74-year-old woman with left eye pain and injection was referred to us. She had a past history of scleral patch graft for necrotizing scleritis after pterygium removal and mitomycin C instillation on her left eye 7 years before. On present examination, a 2.5- to 3.0-mm yellowish-white calcification-like mass was present on the nasal sclera and cornea, and it moved slightly with blinking. The anterior chamber was shallow, and cornea was suspected to be perforated under this object.

RESULTS

This yellowish-white mass was surgically removed. Pathologic examination demonstrated that the specimen was not a calcification but a biofilm formation by many gram-positive bacilli with neutrophils. Corynebacterium was highly suspected as the causative agent of this unusual mass because of the earlier culture of the discharge before referral.

CONCLUSION

The current case demonstrates that bacterial biofilms can be formed on the ocular surface without the involvement of biomaterials.