Clarithromycin for experimental Staphylococcus aureus keratitis

A Mouse Model for Ocular Surface Staphylococcus aureus Infection

Creation of an appropriate animal model that accurately reflects the disease and host immune response to bacterial infection in humans is a major challenge in ocular-surface infection research. For decades, mice have been the ideal small animal model for ocular-surface infection research because of the availability and relatively low cost of various genetic backgrounds, targeted defects, and immunologic reagents. By employing different combinations of mouse and bacterial strains, murine infection models can be used to explore a complete picture of bacterial infection and innate immunity of the ocular surface. A murine model of Staphylococcus aureus infection under normal ocular circumstances is presented here as a convenient and tractable model system in which to study mammalian host responses to pathogens. © 2017 by John Wiley & Sons, Inc.

Ocular penetration and pharmacokinetics of topical clarithromycin eye drops to rabbits

PURPOSE

To evaluate the ocular pharmacokinetics of clarithromycin (CLA) eye drops topically applied to the corneas of rabbits.

METHODS

One 50-μL drop of CLA (0.25%) was administered to each New Zealand white rabbit in a single dose group, and one 50-μL drop of CLA was administered 6 times at 5-min intervals to each rabbit in a loading dose group. The effect of debridement on corneal penetration was also investigated in a de-epithelium group. The drug concentrations in the cornea and aqueous humor (AH) were assayed using high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) analysis.

RESULTS

Maximum CLA levels were achieved in the corneas and AH at 15 and 60 min, respectively, in the intact epithelium eyes in the single dose group (24.54±10.64 μg/g and 0.78±0.22 μg/mL, respectively, mean±the standard error of the mean, n=8). In the loading dose group, 30 min after the last application, the CLA level in the corneas reached 92.26±17.62 μg/g. In the loading dose group, the drug levels in the corneas and AH were significantly increased compared with the drug levels in the corneas with the intact epithelium and de-epithelium eyes in the single dose group at the corresponding time points (P<0.05). The estimated CLA half-lives in the corneas and AH for the intact eyes were 103.28 and 132.61 min, respectively.

CONCLUSION

Therapeutic CLA levels can be achieved in rabbit corneas after topically applying the drug with eye drops.

Animal models of bacterial keratitis

Bacterial keratitis is a disease of the cornea characterized by pain, redness, inflammation, and opacity. Common causes of this disease are Pseudomonas aeruginosa and Staphylococcus aureus. Animal models of keratitis have been used to elucidate both the bacterial factors and the host inflammatory response involved in the disease. Reviewed herein are animal models of bacterial keratitis and some of the key findings in the last several decades.

Effectiveness of Topical TaurolidineversusCiprofloxacin, Ofloxacin, and Fortified Cefazolin in a RabbitStaphylococcusaureusKeratitis Model

PURPOSE

Taurolidine is a broad-spectrum, non antibiotic antimicrobial agent, not previously tested against the common causes of bacterial keratitis. This study, employing an experimental rabbit model of Staphylococcus aureus keratitis, investigated the effectiveness of topical taurolidine in reducing the number of bacteria, and its effectiveness was compared with topical ciprofloxacin, ofloxacin, and 5% cefazolin.

METHODS

The right corneas of all rabbits were intrastromally injected with 100 colony-forming units of Staphylococcus aureus ATCC strain 25923. The animals were divided into the following seven groups: Group 1 (6 rabbits) received taurolidine, group 2 (6 rabbits) received ciprofloxacin, group 3 (6 rabbits) received ofloxacin, group 4 (6 rabbits)received cefazolin, group 5 (5 rabbits) received polyvinylpyrrolidone (vehicle),group 6 (4 rabbits) received sterile water, and group 7 (4 rabbits) was left un-treated (control group). The eyes were topically treated every 30 min with the above-mentioned substances from 4 to 9 h postinjection. One hour after the last drop administration (at 10 h postinjection), signs of inflammation were scored in a masked fashion by slit-lamp examination. Then, their corneas were processed. The number of colony-forming units (cfu) per cornea in all eyes was also determined.

RESULTS

All antimicrobial (taurolidine, ciprofloxacin, ofloxacin, and cefazolin) treatments significantly reduced cfu numbers and slit-lamp examination scores compared with untreated eyes, eyes that received the vehicle, or eyes with sterile water (all p values <0.05). Regarding cfu numbers, although taurolidine therapy was significantly less effective than ciprofloxacin or ofloxacin,there was no significant difference between taurolidine and cefazolin groups.However, taurolidine had similar clinical examination scores with the other antimicrobials, while it had lower scores than the vehicle, sterile water, or un-treated eyes.

CONCLUSIONS

The results obtained in this study suggest that topicaltaurolidine is an effective, novel ocular chemotherapeutic agent for the therapy of rabbit experimental Staphylococcus aureus keratitis. This drug may be a useful and promising ocular antimicrobial.

A comparison of topical chlorhexidine, ciprofloxacin, and fortified tobramycin/cefazolin in rabbit models of Staphylococcus and Pseudomonas keratitis

AIMS

Chlorhexidine was evaluated as a potential topical therapy for experimental bacterial keratitis.

METHODS

Chlorhexidine (0.01%) was compared to ciprofloxacin (0.3%) and tobramycin (1.36%)/cefazolin (5%) both in vitro and in vivo for the treatment of Staphylococcus aureus and Pseudomonas aeruginosa infections. The minimum inhibitory concentration (MIC) was established for each organism for each antibiotic, using a standardized method. One thousand (1000) colony-forming units (CFU) of S. aureus or P. aeruginosa was intrastromally injected into rabbit cornea. A total of 92 corneas were infected and then treated topically with antibiotics. The control eyes were treated with artificial tears. The rabbits were later sacrificed, and the corneal buttons were harvested.

RESULTS

The MIC for chlorhexidine was <or=40 microg/mL for both organisms. In the rabbit model of S. aureus keratitis, following the treatments, the median number of CFU of recoverable bacteria for chlorhexidine (n = 10), ciprofloxacin (n = 12), tobramycin/cefazolin (n = 12), and controls (n = 10) was 1.1 x 10(3), 4.7 x 10(4), 1.9 x 10(5), and 6.7 x 10(4), respectively. For S. aureus, the only treatment that showed a statistically significant reduction in CFU was chlorhexidine. In the P. aeruginosa keratitis group, CFU were significantly reduced with all treatments, compared to the control.

CONCLUSIONS

Chlorhexidine short-term treatment was an effective topical therapy for bacterial keratitis in the rabbit model, when compared with ciprofloxacin and tobramycin/cefazolin, in particular for S. aureus.

A Staphylococcus aureus mouse keratitis topical infection model: Cytokine balance in different strains of mice

Staphylococcus is a leading cause of the potentially blinding disease microbial keratitis. Even with the use of antibiotic therapy, the host inflammatory response continues to damage the cornea, which may lead to blindness. Manipulation of the host response may help improve patient outcome from this devastating disease. We aim to understand the contribution of the host response to Staphylococcus aureus infection. A S. aureus keratitis mouse model was developed in both C57BL/6 and BALB/c mice using two different strains of S. aureus (8325-4 and Staph 38). Twenty-four hours postinfection, mice were killed and eyes were harvested for enumeration of bacteria, polymorphonuclear leucocytes, chemokines and cytokines. The laboratory strain 8325-4 was not as virulent as the clinical isolate Staph 38. In vitro data showed a 250-fold increase in invasion of human corneal epithelial cells by Staph 38 compared to 8325-4. BALB/c mice were susceptible to S. aureus infection whereas C57BL/6 mice were resistant. The resistant C57BL/6 mice were polarized towards a Th2 response, which may be protective for these mice. IL-4, IL-10 and IL-6 were elevated significantly in C57BL/6 mice infected with Staph 38 (P < 0.05). Macrophage inflammatory peptide (MIP)-2 was also significantly elevated in C57BL/6 mice (P < 0.001). The susceptible BALB/c mice had a muted cytokine response, which suggests that S. aureus might be 'walled off' during infection and might avoid host defences. IL-4, IL-10 and IL-6 cytokines may be protective during Gram-positive corneal infection and therefore may be useful for adjunct therapies in the treatment of this disease.

Corneal ulceration in pediatric patients: a brief overview of progress in topical treatment

Pediatric microbial keratitis is a rare but potentially devastating condition. The condition is similar to adult microbial keratitis, but is often characterized by a more severe inflammatory response. The micro-organisms that cause microbial keratitis in children are similar to the causative agents in adults, with herpes simplex and bacteria being the predominant causative agents, and fungi being less frequent. Of the bacterial pathogens, Pseudomonas aeruginosa, Staphylococcus aureus and alpha-hemolytic streptococci are common. The risk factors for pediatric keratitis include colonization of the eyes during birth and trauma to the cornea. Certain microbial factors involved in microbial keratitis are common to all micro-organisms, including adhesion to the cornea, penetration into the cornea, destruction of the corneal stroma (usually by microbial and/or host proteases), and recruitment of white blood cells to help defend the eye. Specific inflammatory responses that occur during pediatric microbial keratitis are not known in detail, but it is likely that cytokines and polymorphonuclear leucocytes are major factors, as they are in adult microbial keratitis. Treatment for pediatric microbial keratitis is usually the same as treatment for adult microbial keratitis; topical application of antimicrobial agents initially, followed by application of anti-inflammatory agents. With pediatric microbial keratitis, extra care must be taken to ensure nontoxicity due to blood adsorption. New microbial keratitis treatments are being developed and these mainly focus on new antimicrobials, antivirulence agents (such as vaccination against microbial toxins) or specific anti-inflammatory agents. There remains a clear need for increased research into the specific responses during microbial keratitis in children which will help progress new therapies as well as the development of new antimicrobials, especially new antifungal therapies.