The antibiotic resistance profiles of Pseudomonas aeruginosa in the Asia Cornea Society Infectious Keratitis Study.

PURPOSE: To describe the prevalence and antibiotic resistance profiles of Pseudomonas aeruginosa isolated from the Asia Cornea Society Infectious Keratitis Study (ACSIKS). METHODS: All bacterial isolates from ACSIKS underwent repeat microbiological identification in a central repository in Singapore. Minimum inhibitory concentration (MIC) determination was conducted for isolates of P. aeruginosa against thirteen antibiotics from 6 different classes, and categorized based on Clinical Laboratory Standard Institutes' reference ranges. The percentage rates of resistance (non-susceptibility) to each antibiotic included isolates of both intermediate and complete resistance. Multi-drug resistance (MDR) was defined as non-susceptibility to at least one agent in three or more antimicrobial classes. RESULTS: Of the 1493 unique bacterial specimens obtained from ACSIKS, 319 isolates were of P. aeruginosa. The majority of isolates were from centers in India (n = 118, 37%), Singapore (n = 90, 28.2%), Hong Kong (n = 31, 9.7%) and Thailand (n = 30, 9.4%). The cumulative antibiotic resistance rate was the greatest for polymyxin B (100%), ciprofloxacin (17.6%) and moxifloxacin (16.9%), and lowest for cefepime (11.6%) and amikacin (13.5%). Isolates from India demonstrated the highest antibiotic resistance rates of all the centers, and included moxifloxacin (47.5%) and ciprofloxacin (39.8%). Forty-eight of the 59 MDR isolates also originated from India. Antibiotic resistance rates were significantly lower in the other ACSIKS centers, and were typically less than 10%. CONCLUSIONS: The antibiotic resistance profiles of P. aeruginosa varied between different countries. While it was low for most countries, substantial antibiotic resistance and a significant number of multi-drug resistant isolates were noted in the centers from India.

A survey of Asian Eye Institutions on perioperative antibiotic prophylaxis in cataract surgery.

PURPOSE: To determine current institutional practice patterns for the use of perioperative antibiotics and other measures to prevent infection after cataract surgery in Asia. METHODS: An online survey-based study of leading eye institutions in China, Hong Kong, India, Indonesia, Japan, Malaysia, Pakistan, Philippines, Singapore, South Korea, Taiwan, Thailand and Vietnam was conducted. The survey was administered to 26 representative key opinion leaders from prominent tertiary eye institutions that are also national academic teaching institutions in Asia. Survey responses were collated and anonymized during analysis. RESULTS: All surveyed institutions used povidone iodine for the preoperative antiseptic preparation of the eye, with notable variations in the concentration of povidone iodine used for conjunctival sac instillation. Preoperative topical antibiotics were prescribed by 61.5% and 69.2% of institutions in low-risk and high-risk cases, respectively. Regarding the use of intra-operative antibiotics, 60.0% and 66.7% of institutions administered intracameral antibiotics in low-risk and high-risk patients, respectively. Postoperative topical antibiotics use patterns were generally very similar in low-risk and high-risk patients. Over half of the institutions (52.2% and 68.0% in low-risk and high-risk patients, respectively) also indicated prolonged postoperative use of topical antibiotics (> 2 weeks). Not all surveyed institutions had established policies/protocols for perioperative antibiotic use in cataract surgery, endophthalmitis surveillance, and/or a monitoring program for emerging antimicrobial resistance. CONCLUSION: There are variations in antimicrobial prophylaxis approaches to preoperative, intra-operative and postoperative regimens in cataract surgery in Asia. More evidence-based research is needed to support the development of detailed guidelines for perioperative antibiotic prophylaxis to reduce postoperative infections.

Evaluation of ligand modified poly (N-Isopropyl acrylamide) hydrogel for etiological diagnosis of corneal infection.

Corneal ulcers, a leading cause of blindness in the developing world are treated inappropriately without prior microbiology assessment because of issues related to availability or cost of accessing these services. In this work we aimed to develop a device for identifying the presence of Gram-positive or Gram-negative bacteria or fungi that can be used by someone without the need for a microbiology laboratory. Working with branched poly (N-isopropyl acrylamide) (PNIPAM) tagged with Vancomycin, Polymyxin B, or Amphotericin B to bind Gram-positive bacteria, Gram-negative bacteria and fungi respectively, grafted onto a single hydrogel we demonstrated specific binding of the organisms. The limit of detection of the microbes by these polymers was between 10 and 4 organisms per high power field (100X) for bacteria and fungi binding polymers respectively. Using ex vivo and animal cornea infection models infected with bacteria, fungi or both we than demonstrated that the triple functionalised hydrogel could pick up all 3 organisms after being in place for 30 min. To confirm the presence of bacteria and fungi we used conventional microbiology techniques and fluorescently labelled ligands or dyes. While we need to develop an easy-to-use either a colorimetric or an imaging system to detect the fluorescent signals, this study presents for the first time a simple to use hydrogel system, which can be applied to infected eyes and specifically binds different classes of infecting agents within a short space of time. Ultimately this diagnostic system will not require trained microbiologists for its use and will be used at the point-of-care.

Polymeric Drug Delivery Devices: Role in Cornea and External Disease.

ABSTRACT: The field of ophthalmic drug delivery is undergoing rapid changes not only in the evolution of pharmacologic agents but also in the novel drug delivery vehicles. The ocular surface has limitations to drug penetration because of the presence of tight junctions between basal epithelial cells, which limits the amount of drug that can be absorbed after topical instillation. In addition, nasolacrimal drainage reduces the precorneal residence time significantly. Contact lenses (CLs) have been considered as possible carriers for topical medications because they reside on the ocular surface for a sufficient length of time, and pharmacologic agents may be copolymerized with hydrogels allowing controlled drug diffusion. This strategy reduces the frequency of dosage while improving compliance. Modification of drug delivery vehicles is essential to allow sustained release of the drug from a polymeric complex, facilitate stability and residence time of the drug on the precorneal tear film, and improve penetration into biologic membranes. This review focuses on updates in CL-based and non-CL-based strategies in ophthalmic drug delivery.

Alterations in the conjunctival surface bacterial microbiome in bacterial keratitis patients.

Microbial keratitis is an infectious disease of the eye, in which the cornea is inflamed. Under severe conditions, keratitis can lead to significant loss of vision and enucleation of the eye. Ocular trauma is the major risk factor causing keratitis and microorganisms viz., bacteria, fungi, viruses are the causative agents. The current study characterized the conjunctival bacterial microbiomes of healthy individuals and individuals with bacterial keratitis (BK) and assessed whether ocular microbiome dysbiosis is prevalent in BK patients. Ocular bacterial microbiomes were generated from the conjunctival swabs of healthy controls (HC-SW) and conjunctival swabs (BK-SW) and corneal scrapings (BK-CR) of BK patients using V3-V4 amplicon sequencing and data analysed using QIIME and R software. The Alpha diversity indices, diversity and abundance of different phyla and genera, heat map analysis, NMDS plots and inferred functional pathway analysis clearly discriminated the bacterial microbiomes of conjunctival swabs of healthy controls from that of BK patients. Preponderance of negative interactions in the hub genera were observed in BK-CR and BK-SW compared to HC-SW. In addition, a consistent increase in the abundance of pathogenic bacteria, as inferred from published literature, was observed in the conjunctiva of BK patients compared to HC and this may be related to causing or exacerbating ocular surface inflammation. This is the first study demonstrating dysbiosis in the ocular bacterial microbiome of conjunctiva of bacterial keratitis patients compared to the eye of healthy controls. The bacterial microbiome associated with the corneal scrapings of keratitis individuals is also described for the first time.

Risk Factors for Contact Lens-Related Microbial Keratitis and Associated Vision Loss in a South Indian Population.

OBJECTIVES: To identify risk factors associated with contact lens-related microbial keratitis (CL-MK) and subsequent vision loss in a south Indian population. METHODS: A retrospective study of medical records at the LV Prasad Eye Institute in Hyderabad, India, of patients diagnosed with CL-MK and of controls who had no history of corneal inflammation during contact lens wear was undertaken. Variables such as demographic data, contact lens wear details, duration of the event, visual acuity, epithelial defect and infiltrate size, and microbiology of the cornea during the event were collected. Differences between cases and controls were analyzed using parametric and nonparametric tests. Logistic regression was used to calculate the odds ratio (OR) and associated 95% confidence intervals in univariate and multivariate analyses for cases vs. controls and for factors associated with vision loss. RESULTS: One hundred sixty-seven cases of CL-MK and 153 controls were included in the analyses. Risk factors associated with the greatest increased OR for CL-related MK were: being in professional employment vs. a student (OR=3.9), disposing lenses yearly versus monthly or biweekly (OR=2.2), and any overnight wear (OR=2.8). Risk factors associated with vision loss were: high myopia (OR=3.6), severe vs. mild severity (OR=16.0), and hypopyon (OR=4.3). CONCLUSIONS: Identification of these risk factors may help inform safe contact lens wear habits and management strategies.

Microneedle ocular patch: fabrication, characterization, and ex-vivo evaluation using pilocarpine as model drug.

Context: Enhacing the ocular bioavailability of drugs after their topical application is a challenge.Objective: The objective of the study was to design, fabricate, and investigate the effectiveness of microneedle ocular patch (MOP) in delivering the model drug, pilocarpine HCl across the corneal membrane.Methods: MOP mimicked commercially available contact lens design elements having a diameter of 14.20 mm and a sagittal height of 3.85 mm with a convex curvature. The base of this patch contained an array of 25 pyramid-shaped microneedles measuring 521 ± 10 µm in length. Pilocarpine loaded MOP was prepared by micromolding technique using dissolvable polyvinyl alcohol and polyvinyl pyrrolidone matrix. MOP was characterized for physical and mechanical properties using a stereomicroscope, scanning electron microscope, and texture analyzer.Results: Histological examination after MOP application on excised human cornea showed penetration of microneedles with a required insertional force of 1.04 ± 0.17 N. Flux of pilocarpine across excised cornea was significantly (p < 0.05) greater after application of MOP (704 ± 149 µg/cm2/h) compared with solution formulation (188 ± 24 µg/cm2/h). Ex-vivo pilocarpine permeation study in porcine eye globe revealed significantly (p < 0.05) greater availability in aqueous humor within 30 min of application of MOP (249 ± 85 µg/ml) compared with solution formulation (46 ± 9 µg/ml).Conclusion: MOP can be developed as a potential ophthalmic drug delivery system.

Thirty years of eye bank experience at a single centre in India.

PURPOSE: The global survey of eye banking and corneal transplantation reveals differences in eye banking trajectories in various countries. There is a need to encourage and lay down foundations of successful eye banking practices in many nations across the world map. The study evaluates demographics, trends in donor cornea retrieval, utilization and eye banking practices in over 30 years at a single eye bank in India. METHODS: A longitudinal descriptive analysis of eye banking practices from 1989 to 2018 at Ramayamma International Eye Bank, Hyderabad, India, was performed. Data on eye donations, practice patterns and various types of keratoplasty were collected. Data were analysed focusing on practices and historical development of the eye bank. RESULTS: Over the years, the eye bank has made use of several advances in its practice patterns and evolved to a stage of self-sustainability. With the fulfilment of internal demand for corneal transplantation, 50% of retrieved corneas could be distributed for community needs outside the institute. Number of transplants increased from 20 in 1987 to 4738 in 2018. Total number of transplants touched 27,746 in 2018 which might be the highest numbers for a single centre anywhere in the world. CONCLUSIONS: The study reveals a dynamic development of the eye bank over the last 30 years and emphasizes the importance of an active quality management in coping with the challenges of modern eye banking. The increasing trend of cornea collection and transplantation is a reflection of the needs and efforts towards treating and eliminating corneal blindness.

Endophthalmitis after cataract surgery: epidemiology, risk factors, and evidence on protection.

PURPOSE OF REVIEW: After publication of the results of the European Society of Cataract and Refractive Surgery (ESCRS) study, there is a lot of enthusiasm for using intracameral antibiotics for the prevention of postcataract endophthalmitis. However, despite level 1 evidence, the practice has not been adopted universally. The aim of this review is to present a summary of the articles published in the last 18 months on this topic. RECENT FINDINGS: The published literature highlights that the incidence rate of endophthalmitis declined after 2007. Simultaneously, there is a rising trend for using intracameral injection of antibiotics at the conclusion of cataract surgery. Although various drugs have been used for this purpose, nearly all provide comparable protection. Industry has started manufacturing formulations for commercial availability of intracameral injection. Innovations are also ongoing to use intraocular lens for drug delivery and developing other intraocular drug delivery devices. SUMMARY: Endophthalmitis prevention is at an interesting crossroad. Although there is hesitation the intracameral injection of antibiotics is increasingly being adopted by physicians, which is likely to grow further with commercial availability of formulations. However, it will be important to be cautious and report all adverse reactions associated with this practice.

Ex vivo rabbit and human corneas as models for bacterial and fungal keratitis.

PURPOSE: In the study of microbial keratitis, in vivo animal models often require a large number of animals, and in vitro monolayer cell culture does not maintain the three-dimensional structure of the tissues or cell-to-cell communication of in vivo models. Here, we propose reproducible ex vivo models of single- and dual-infection keratitis as an alternative to in vivo and in vitro models. METHODS: Excised rabbit and human corneoscleral rims maintained in organ culture were infected using 108 cells of Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans or Fusarium solani. The infection was introduced by wounding with a scalpel and exposing corneas to the microbial suspension or by intrastromal injection. Post-inoculation, corneas were maintained for 24 and 48 h at 37 °C. After incubation, corneas were either homogenised to determine colony-forming units (CFU)/cornea or processed for histological examination using routine staining methods. Single- and mixed-species infections were compared. RESULTS: We observed a significant increase in CFU after 48 h compared to 24 h with S. aureus and P. aeruginosa. However, no such increase was observed in corneas infected with C. albicans or F. solani. The injection method yielded an approximately two- to 100-fold increase (p < 0.05) in the majority of organisms from infected corneas. Histology of the scalpel-wounded and injection models indicated extensive infiltration of P. aeruginosa throughout the entire cornea, with less infiltration observed for S. aureus, C. albicans and F. solani. The models also supported dual infections. CONCLUSIONS: Both scalpel wounding and injection methods are suitable for inducing infection of ex vivo rabbit and human cornea models. These simple and reproducible models will be useful as an alternative to in vitro and in vivo models for investigating the detection and treatment of microbial keratitis, particularly when this might be due to two infective organisms.

Precut cornea for Descemet's stripping endothelial keratoplasty: experience at a single eye bank.

The aim of the study is to describe the experience with precut facility for endothelial keratoplasty at a single eye bank affiliated to a tertiary eye care center in India. Data on precut tissues from Nov 2012 to Dec 2014 were retrospectively reviewed from the electronic database of the eye bank of a tertiary eye care center in South India. Donor characteristic data including donor age, precut and postcut endothelial cell density (ECD), recipient age, and thickness of graft were collected. The number of precuts increased from 42 in 2012 (Nov and Dec) and 422 in 2013 to 584 in 2014. Of the total of 1048 precuts, seven (0.67 %) were miscut and could not be utilized for transplants. The donor age ranged from 2 to 89 years. A mean change of 43.6 ± 325.2 cells/mm2 in ECD was noted after cut, proportional increase in mean being 1.9 %. The change in ECD after cut was negatively correlated with ECD before cut. The recipient age ranged from 1 to 89 years. The median thickness of donor lenticule after cut was 148 µm (interquartile range 131-166 µm). Analysis of precut donor corneas from a single eye bank shows that the ECD of the processed tissues was excellent for transplantation. The tissue wastage in the hands of eye bank personal was minimal.

Update on fungal keratitis.

PURPOSE OF REVIEW: The aim of this review article is to present an overview of some of the seminal work published in the last 18 months (July 2014 to December 2015). RECENT FINDINGS: The published literature highlights the need for the identification of fungal isolates to species and subspecies level using molecular methods. Molecular methods helped us identify some of the unknown fungi such as Pythium - fungi that causes keratitis unresponsive to conventional antifungal therapy. Although not popular fungal in-vitro susceptibility tests are showing better correlation between resistance and clinical outcomes. Several groups are trying to understand host responses controlling disease production as well as inflammation. On therapy front researchers are working to develop drug formulations and delivery systems that will provide superior pharmacokinetics and bioavailability. Collagen cross-linking and injections of antifungal agents into the corneal stroma and anterior chamber continue to be attractive to clinicians and more and more researchers are publishing their experiences. SUMMARY: It is an interesting time in the history of mycotic keratitis with a lot of positive developments. Molecular methods will help improved diagnosis and clinico-therapeutic correlation. Drug delivery devices with superior pharmacokinetics are on horizon.

Image quality analysis of pseudophakic eyes with uncorrected astigmatism.

PURPOSE: To determine the combined impact of uncorrected astigmatism, pupil diameter, and wavefront aberrations on the distance and near visual performance of pseudophakic eyes with monofocal intraocular lens (IOL) implants using objective image quality (IQ) metrics. METHODS: Monocular distance (4 m) and near (40 cm) logMAR acuities of 15 emmetropic pseudophakic eyes were obtained without astigmatism and with 2.5 diopters myopic to 2.5 diopters hyperopic astigmatism induced along a 90-degree axis. The IQ metrics were calculated from the participant's wavefront aberrations and habitual pupil diameter for all values of astigmatism and correlated with logMAR acuity. The analysis was repeated without higher-order aberrations (HOAs) and with the entire wavefront data for 6-, 3-, and 1.5-mm pupil diameters. RESULTS: Distance acuity deteriorated with uncorrected astigmatism (p < 0.01), whereas near acuity improved with uncorrected myopic astigmatism and deteriorated with uncorrected hyperopic astigmatism (both p < 0.01). The logEW IQ metric showed the best correlation with logMAR acuity (r = 0.86). Distance logEW values deteriorated whereas near logEW values improved in the presence of HOAs for all values of uncorrected astigmatism (p < 0.01). Distance logEW values for 6- and 3-mm pupil diameters were worse than that of the 1.5-mm pupil diameter for all values of uncorrected astigmatism and for both viewing distances (p < 0.01). CONCLUSIONS: Image quality metrics analysis can be used successfully to determine the impact of uncorrected astigmatism, pupil diameter, and HOAs on the distance and near logMAR acuities of pseudophakic eyes with monofocal IOL implants. The improvement in near IQ with uncorrected myopic astigmatism and HOAs suggests that these two factors supplement each other to improve near visual performance of pseudophakic eyes. Such an improvement in near vision is however associated with a loss of distance vision in these eyes.

Binocular vision of bilaterally pseudophakic eyes with induced astigmatism.

PURPOSE: Induced myopic astigmatism improves the monocular near logMAR (logarithm of the minimal angle of resolution) acuity of pseudophakes with monofocal intraocular lens implants but with a small loss in distance acuity. The impact of induced astigmatism on binocular vision of pseudophakes remains unknown. This study determined the impact of bilaterally induced astigmatism on binocular distance and near logMAR and stereoacuity of bilateral pseudophakes with monofocal intraocular lens implants. METHODS: Distance (3 m) and near (40 cm) logMAR acuity and near (40 cm) stereoacuity were measured in 15 bilateral pseudophakes with 10 different combinations of induced astigmatism. Combinations were chosen such that one eye had no astigmatism or 1 diopter (D) myopic astigmatism at 90 degrees axis or 1 D hyperopic astigmatism at 90 degrees axis. The fellow eye had the same error or that with orthogonal axis (180 degrees) or different magnitude (2.5 D) or opposite polarity. RESULTS: Distance logMAR acuity deteriorated by up to 0.2 logMAR units from median best-corrected values (-0.06 logMAR) only for bilaterally induced (p < 0.01) but not for unilaterally induced (p > 0.9) astigmatism. Near logMAR acuity and stereoacuity improved by up to 0.25 logMAR units and 130 arc sec from their respective median uncorrected values (0.65 logMAR and 225.8 arc sec) for induced myopic astigmatism (p < 0.001). Near acuity was similar or worse than uncorrected values for induced hyperopic astigmatism (p ≥ 0.003). Stereoacuity was better with parallel than with orthogonal axes of induced myopic astigmatism in the two eyes (p = 0.001). LogMAR acuity did not change with axis of astigmatism in the two eyes (p > 0.6). CONCLUSIONS: Distance and near logMAR acuity and stereoacuity of bilateral pseudophakes vary with the combination of astigmatism induced before two eyes. Combinations with myopic astigmatism partly benefit binocular near vision, albeit with a loss of distance vision. Near stereoacuity is better with parallel than with orthogonal axes of myopic astigmatism in the two eyes. Visual performance is equal to or worse than uncorrected condition for hyperopic astigmatism.

Microbial analyses of contact lens-associated microbial keratitis.

PURPOSE: To investigate the utility of additional microbial analyses to detect the causative microorganism of microbial keratitis and to determine the strength of association between clinical variables. METHODS: This retrospective study included 125 eyes of 123 people presenting with presumed infectious keratitis associated with contact lens wear, and examined between January 2001 and November 2011. RESULTS: Sixty-three male and 60 female patients with a mean age of 24.14 ( ±6.7) and 26.7 (±10.0) years, respectively, were included in the study. Among the samples tested, 38 (40%) corneal cultures, 85 (92%) contact lens cultures, and 49 (80%) contact lens case cultures yielded positive results. In the samples for which all microbial investigations were performed and corneal culture was positive, cultures of contact lenses and corneas yielded the same microbes in 94% of cases, and for contact lens case and corneal cultures 77% of cases yielded the same microbes. Importantly, these were monocultures of the same microbe isolated from the cornea in the contact lens and lens case cultures. The odds of having a positive corneal culture was 37 times higher (p = 0.008) when patients presented to the clinic 2 weeks after the onset of symptoms. Pseudomonas aeruginosa was the predominant organism isolated, and most isolates were susceptible to commonly used antimicrobials. CONCLUSIONS: Contact lens culture might be an effective test to perform to detect and determine the causative microorganism when corneal cultures are unavailable or yield no microorganisms upon culture. A longer duration of symptoms before presenting to the clinic was significantly associated with obtaining a positive corneal culture.

Functionalized chitosan based antibacterial hydrogel sealant for simultaneous infection eradication and tissue closure in ocular injuries.

Management of infections at ocular injury often requires prolonged and high dose of antibiotic, which is associated with challenges of antibiotic resistance and bacterial biofilm formation. Tissue glues are commonly used for repairing ocular tissue defects and tissue regeneration, but they are ineffective in curing infection. There is a critical need for antibacterial ocular bio-adhesives capable of both curing infection and aiding wound closure. Herein, we present the development of an imine crosslinked N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride (HTCC)­silver chloride nanocomposites (QAm1-Agx) and poly-dextran aldehyde (PDA) based bactericidal sealant (BacSeal). BacSeal exhibited potent bactericidal activity against a broad spectrum of bacteria including their planktonic and stationary phase within a short duration of 4 h. BacSeal effectively reduced biofilm-embedded MRSA and Pseudomonas aeruginosa by ∼99.99 %. In ex-vivo human cornea infection model, BacSeal displayed ∼99 % reduction of ocular infection. Furthermore, the hydrogel exhibited excellent sealing properties by maintaining ocular pressure up to 75 mm-Hg when applied to human corneal trauma. Cytotoxicity assessment and hydrogel-treated human cornea with a retained tissue structure, indicate its non-toxic nature. Collectively, BacSeal represents a promising candidate for the development of an ocular sealant that can effectively mitigate infections and may assist in tissue regeneration by sealing ocular wounds.

Efficacy of a Novel Antibiotic Drug Combination Toward Multidrug-Resistant Ocular Pathogens.

PURPOSE: Antimicrobial resistance is a global health threat, compounded by the reduction in the discovery of new antibiotics. A repurposed drugs-based approach could provide a viable alternative for the treatment of multidrug-resistant (MDR) bacterial infections. In this study, we sought to evaluate the in vitro efficacy of a novel drug combination, polymyxin B/trimethoprim (PT) + rifampin on MDR isolates from patients with bacterial keratitis in India. METHODS: Forty-three isolates, which included 20 Staphylococcus aureus , 19 Pseudomonas aeruginosa , 3 Pseudomonas stutzeri , and 1 Acinetobacter baumannii , were evaluated for their antibiotic resistance by minimum inhibitory concentration (MIC). Fractional Inhibitory Concentration Index (FICI) testing was performed to measure the antimicrobial impact of PT + rifampin in combination. RESULTS: Among S. aureus isolates, 100% were resistant to at least 1 antibiotic class, 12 (60%) were MDR, and 14 (70%) were classified as methicillin-resistant. Among the gram-negative isolates, >90% were classified as MDR. Fractional Inhibitory Concentration (FIC) testing revealed that PT + rifampin was effective in completely inhibiting growth of all isolates while also displaying additive or synergistic activity in approximately 70% of the strains. Mean FICI values were 0.753 ± 0.311 and 0.791 ± 0.369 for S. aureus and gram-negative isolates, respectively, and a >2-fold reduction in MIC was measured for both PT and rifampin when tested in combination versus alone. CONCLUSIONS: Our data demonstrate the ability of PT + rifampin to eliminate all isolates tested, even those conferring MDR, highlighting the promise of this drug combination for the treatment of bacterial keratitis.