Microbial keratitis is a potentially blinding condition that must be treated emergently to preserve vision. Although long recognized as a significant cause of corneal blindness, our understanding of its true global scale, associated burden of disease, and etiological patterns remains somewhat limited. Current epidemiological data suggest that microbial keratitis may be epidemic in parts of the world-particularly within South, SouthEast , and East Asia-and may exceed 2 million cases per year worldwide. Etiological patterns vary between economically developed and developing countries, with bacterial predominance in the former and fungal predominance in the latter. The key to effective management lies in timely diagnosis; however, the current gold standard of stain and culture remains time consuming and often yields no clinically useful results. For this reason, there are attempts to develop highly sensitive and accurate molecular diagnostic tools to provide rapid diagnosis, inform treatment decision making, and minimize the threat of antimicrobial resistance. We provide an overview of these key areas and of avenues for further research toward the goal of more effectively addressing the problem of microbial keratitis on both an individual and public health level.

Streptococcus pneumoniae, an inhabitant of the upper respiratory mucosa, causes respiratory and invasive infections as well as conjunctivitis. Strains that lack the capsule, a main virulence factor and the target of current vaccines, are often isolated from conjunctivitis cases. Here we perform a comparative genomic analysis of 271 strains of conjunctivitis-causing S. pneumoniae from 72 postal codes in the US. We find that the vast majority of conjunctivitis strains are members of a distinct cluster of closely related unencapsulated strains. These strains possess divergent forms of pneumococcal virulence factors (such as CbpA and neuraminidases) that are not shared with other unencapsulated nasopharyngeal S. pneumoniae. They also possess putative adhesins that have not been described in encapsulated pneumococci. These findings suggest that the unencapsulated strains capable of causing conjunctivitis utilize a pathogenesis strategy substantially different from that described for S. pneumoniae at other infection sites.

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.

With the use of these methods, bacterial detection was improved from 47.6% to 95.3%, demonstrating them to be sensitive, rapid tests for diagnosis of bacterial endophthalmitis.

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BackgroundThe purpose of this paper is to describe clinical characteristics and determine correlations between clinical outcomes and antifungal susceptibility among molecularly characterized ocular Fusarium isolates in Brazil.MethodsForty-one Fusarium isolates obtained from 41 eyes of 41 patients were retrieved from the ophthalmic microbiology laboratory at São Paulo Federal University and grown in pure culture. These isolates were genotyped and antifungal susceptibilities determined for each isolate using a broth microdilution method. The corresponding medical records were reviewed to determine clinical outcomes.ResultsThe 41 isolates were genotypically classified as Fusarium solani species complex (36 isolates, 88%), Fusarium oxysporum species complex (two isolates, 5%), Fusarium dimerum species complex (one isolate, 2%) and two isolates that did not group into any of the species complexes. Final best corrected visual acuity varied from 20/20 to light perception and was on average 20/800 (logarithm of the minimum angle of resolution (LogMAR) 1.6). A history of trauma was the most common risk factor, being present in 21 patients (51%). Therapeutic penetrating keratoplasty was necessary in 22 patients (54%). Amphotericin B had the lowest minimum inhibitory concentration for 90% of isolates (MIC90) value (2 μg/mL) and voriconazole had the highest (16 μg/mL). There was an association between a higher natamycin MIC and need for therapeutic penetrating keratoplasty (Mann–Whitney test, P < 0.005).ConclusionTrauma was the main risk factor, and therapeutic penetrating keratoplasty was necessary in 54% of patients. Amphotericin B had the lowest MIC90 (2 μg/mL) of the three antifungal agents tested. There was an association between higher natamycin MIC levels and corneal perforation, emphasizing the need for antifungal susceptibility testing and tailoring of antifungal strategies.

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Purpose: To study the prevalence of methicillin-resistant Staphylococcus aureus among S. aureus ocular infections in a tertiary health center in Brazil and compare antibiotic susceptibility patterns between MRSA and methicillin-susceptible S. aureus isolates. Methods: Electronic records from the ocular microbiology laboratory of the Universidade Federal de São Paulo were retrospectively reviewed. During a 10-year period (between January 2000 and December 2009) all conjunctivitis, keratitis, and endophthalmitis cases with a positive culture for S. aureus were identified. Antibiotic susceptibility was determined using the Kirby-Bauer disk diffusion method. Results: Five hundred sixty-six S. aureus isolates were identified; of those, 56 (9.9%) were resistant to methicillin. Throughout the 10-year period, Staphylococcus aureus showed a significant increasing trend from 7.55% to 16.18% among overall S. aurues infections (p=0.001) and from 3.7% to 13.16% in conjunctivitis (p=0.001). Conversely, we did not observe the same trend among those with keratitis (p=0.38). Staphylococcus aureus isolates showed higher resistance rates to tobramycin, gentamicin, ciprofloxacin, gatifloxacin, and moxifloxacin when compared with S. aureus isolates (p< 0.001). All cases were susceptible to vancomycin. Conclusion:We observed an increasing trend in the overall prevalence of Staphylococcus aureus ocular infections and statistically significant higher resistance rates to commonly used antibiotics compared to Staphylococcus aureus. Our data supports the need for constant bacterial surveillance and should be taken into consideration before initiating empiric treatment of ocular infections. Keywords