Measurement of AQCmax of Five Different Ophthalmic Solutions and Discussion of Its New Application

In Vitro Antimicrobial Activity of Quinolones Against Major Bacterial Isolates from the Ocular Surface Bacterial Flora of Tertiary Hospital Patients in Japan

Purpose: To determine the in vitro antimicrobial activity of quinolones against major bacterial isolates from the ocular surface bacterial flora of patients in a tertiary hospital for selection of optimal antibiotic eye drop during the perioperative stage. Methods: The conjunctival sac scraping of 933 patients who underwent ophthalmic surgery was cultivated and bacterial species of the isolates were identified. The minimum inhibitory concentrations (MICs) of gatifloxacin (GFLX), moxifloxacin (MFLX), levofloxacin (LVFX), and tosufloxacin (TFLX) were measured by microdilution methods. The cumulative percentages of MICs of 4 quinolones against major bacteria were calculated. The concentrations of quinolones inhibiting 50% (MIC₅₀) and 90% (MIC₉₀) of the major bacteria were compared. Results: The study mainly included 784 patients scheduled for cataract surgery, 73 for vitrectomy, 30 for corneal transplantation, 30 for conjunctival surgery, 11 for eyelid surgery. The most frequently isolated bacterium was coagulase-negative Staphylococci (CNS) (184 strains), followed by Corynebacterium (107 strains), Staphylococcus aureus (33 strains), Streptococcus (18 strains), and Enterococcus (13 strains). The percentages of methicillin-sensitive CNS isolates for which MIC of GFLX, MFLX, LVFX, and TFLX was 0.06 μg/mL or less were 8.0%, 13.4%, 5.4%, and 63.4%, respectively. Similarly, the percentage for Corynebacterium was 23.0%, 23.0%, 0%, and 35.6%, respectively. MIC₅₀ of TFLX for Streptococcus and Enterococcus showed the lowest values, 0.12 and 0.25 μg/mL, respectively. Conclusions: Among 4 quinolones, TFLX has the highest in vitro antimicrobial activity against major bacterial isolates from the ocular surface bacterial flora of patients in a tertiary hospital.

A super-infection in the cornea caused by Stemphylium, Acremonium, and α-Streptococcus

Background

Polymicrobial keratitis with fungus and bacteria can lead to blindness and is challenging to treat. Here, we introduce a case of fungal keratitis caused by two different strains in addition to definite bacterial super-infection caused by an α-Streptococcus sp., and describe the importance of microscopic examination.

Case presentation

A 74-year-old woman, who had a past history of infection with leprosy, presented with conjunctival hyperaemia, pain, and corneal opacity in her right eye. Under the presumptive diagnosis of infectious keratitis, corneal scrapings were stained by various reagents and inoculated on several agar plates. Microscopic findings of the scrapings revealed fungi and a small number of Gram-positive cocci. Multiple anti-fungal therapies with levofloxacin ophthalmic solution were administered. Although empiric treatment was initially effective, keratitis recurred 10 days after its initiation. Repeated corneal scraping revealed an abundance of Gram-positive chain cocci and a small amount of fungi, resulting in the switching of an antibiotic medication from levofloxacin to moxifloxacin and cefmenoxime. Keratitis resolved gradually after the conversion. Stemphylium sp., Acremonium sp., and α-Streptococcus sp. were simultaneously isolated from the corneal scrapings.

Conclusions

To the best of our knowledge, this is the first case of fungal keratitis caused by Stemphylium sp., and also the first case of super-infection in the cornea caused by two different fungi and one bacterium. Microscopic examination of the corneal scrapings was beneficial in rapid decision of changing to appropriate drug according to the dominancy of pathogenicity.

Current knowledge about and recommendations for ocular methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is the most important and common pathogen that infects patients following cataract surgery, laser in situ keratomileusis, and photorefractive keratectomy. It is reported to be the second most common pathogen causing bacterial keratitis around the world. Of special concern are increasing reports of postoperative methicillin-resistant S aureus (MRSA) infection. For example, MRSA wound infections have been reported with clear corneal phacoemulsification wounds, penetrating keratoplasty, lamellar keratoplasty, and following ex vivo epithelial transplantation associated with amniotic membrane grafts. These and other data suggest that MRSA has become increasingly prevalent worldwide. In this article, we review the current medical literature and describe the current challenge of ocular MRSA infections. Recommendations are made based on an evidence-based review to identify, treat, and possibly reduce the overall problem of this organism.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Challenges in assessing microbial susceptibility and predicting clinical response to newer-generation fluoroquinolones

PURPOSE

To determine the most appropriate methods for assessing the potential effectiveness of the newer topical fluoroquinolones gatifloxacin, moxifloxacin, and besifloxacin.

METHODS

This article is based on a literature search for published articles about the pharmacokinetic (PK) and pharmacodynamic (PD) characteristics of and measure of bacterial susceptibility to topical ophthalmic fluoroquinolones. Search terms included fluoroquinolones, susceptibility, resistance, minimal/minimum inhibitory concentration (MIC), PDs, PKs, and ocular, ophthalmic, or topical antibiotics.

RESULTS

Topical fluoroquinolones, particularly besifloxacin, gatifloxacin, and moxifloxacin, have become important treatment options for common ocular bacterial infections due to their broad-spectrum bactericidal activity and low toxicity. An important challenge in ophthalmology is identifying the most accurate in vivo and in vitro methods for evaluating the efficacy of these topical fluoroquinolones. The MIC is the most commonly used measure of in vitro susceptibility. In systemic therapy, this measure is combined with PK data of antibiotics to generate PD indices PK/PD whose breakpoints differentiate clinically susceptible from nonsusceptible bacterial pathogen populations. PD breakpoints are further tested in prospective studies for their ability to predict clinical efficacy. However, it is not known whether systemically derived breakpoints apply to the assessment of clinical susceptibility to ocular agents. Topical ocular antibiotics likely achieve higher concentrations at the target site than do systemically administered antibiotics, but these higher concentrations can be quickly reduced by reflex tearing and blinking induced by instillation. Hence, studies have been conducted in animals and humans to determine the PK concentrations of topically administered antibiotics in ocular compartments. When combined with MIC values for topical pathogens, the results have the potential to predict clinical efficacy after identification of the appropriate PK/PD target. Ocular studies incorporating PK/PD assessments have recently begun to be reported with newer fluoroquinolones, including besifloxacin, gatifloxacin, and moxifloxacin, whose prolonged contact time and potent bactericidal activity have translated into some of the most favorable PK/PD target values. However, the clinical relevance of these studies has yet to be determined.

CONCLUSION

There is still a clear need for predictive models to extend our understanding of the clinical susceptibility of ocular pathogens.