Methicillin-resistant Staphylococcus aureus keratitis in the rabbit: therapy with ciprofloxacin, vancomycin and cefazolin

Topical Vancomycin is More Efficient than Povidone-Iodine Treatment in Controlling Bacterial Growth in Methicillin-Resistant Staphylococcus Aureus Keratitis Model in Rabbits

To evaluate the efficacy of topical vancomycin and povidone iodine (PI) application on methicillin-resistant Staphylococcus aureus (MRSA) keratitis model in rabbits.

MRSA keratitis was induced by injecting 0.1 mL MRSA containing 1000 colony-forming units (CFU) into central cornea of right eyes of 24 New Zealand White rabbits. Animals were divided into four groups (n = 6): control (treated with balanced salt solution), 50 mg/mL topical vancomycin, 5% topical PI, and combination; examined before and after treatment, and corneal tissues were harvested for analysis at 9th hour of treatment.

Bacterial load was determined as: 7.63 ± 0.82 log10 CFU/g in control group, 6.95 ± 1.66 log10 CFU/g in PI group, 4.67 ± 0.77 log10 CFU/g in combination group, and 4.33 ± 0.71 log10 CFU/g in vancomycin group (p = 0.001). Median of total clinical score increased significantly from 7 [range: 5-8] to 11.5 [range: 11-15] (p = 0.001) in control group, did not change (6 [range: 5-8] to 7 [range: 5-7]; p = 0.695) in vancomycin group, increased significantly from 7 [range: 5-8] to 12.5 [range: 10-14] (p < 0.001) in PI group, increased significantly from 6.5 [range: 5-7] to 8 [range: 7-9] in combination group (p = 0.002). Post-treatment clinical scores for chemosis, conjunctival injection, iritis, hypopyon, epithelial erosion, and corneal infiltrate were significantly lower in vancomycin-treated groups compared to others (p < 0.05). In PI-treated groups, especially scores for chemosis, conjunctival injection, epithelial erosion and corneal infiltrate were significantly higher than vancomycin (p < 0.05).

Topical vancomycin significantly inhibited bacterial growth in MRSA keratitis. However, PI was ineffective in controlling this growth; additionally, exerted toxic effect on ocular surface. When vancomycin was combined with PI, no additional increase in efficacy of treatment was detected compared to only vancomycin.

Ciprofloxacin Ophthalmic Solution in the Treatment of Conjunctivitis and Blepharitis: A Comparison with Fusidic Acid

The efficacy and safety of ciprofloxacin ophthalmic solution (0.3%) and fusidic acid gel (1%) were compared in the treatment of bacterial conjunctivitis and blepharitis in a randomized, open, parallel group study. Thirty-nine patients, 21 treated with ciprofloxacin solution and 18 treated with fusidic acid gel, were culture-positive on admission and were evaluable for efficacy. At the end of a 7-day treatment, the infecting organism was eradicated in 81% of those treated with ciprofloxacin and 72% of those treated with fusidic acid gel. There was clinical cure or improvement in 95% and 89% respectively. The clinical cure rate appeared to be higher with ciprofloxacin than fusidic acid (62% compared with 28%) but this was related to the higher proportion of patients with acute conjunctivitis in the ciprofloxacin group. Two patients using ciprofloxacin had mild discomfort and stinging on instillation and one given fusidic acid had moderate edema and discomfort; the latter patient stopped treatment. Topical ciprofloxacin is effective and well tolerated and is a useful treatment of bacterial conjunctivitis and blepharitis.

Ciprofloxacin Ophthalmic Solution versus Rifamycin Ophthalmic Solution for the Treatment of Conjunctivitis and Blepharitis

The efficacy and safety of ciprofloxacin (0.3%) ophthalmic solution and rifamycin (1%) ophthalmic solution for the treatment of bacterial conjunctivitis and blepharitis was compared in this randomized, double-masked, parallel-group study. Forty-one patients, 19 on ciprofloxacin and 22 on rifamycin, were culture-positive on admission and evaluated for efficacy. There was clinical improvement in more than 90% of patients in each group at the end of the seven-day treatment period. However, clinical cure rates on day 7 appeared to be higher with ciprofloxacin (53%) than rifamycin (23%; p = 0.061, Mann-Whitney test). Bacteriological eradication rates were comparable: the infecting organisms were eradicated in 68% of patients on ciprofloxacin and 77% with rifamycin. There were no serious adverse reactions to either treatment. One patient in each group was withdrawn on account of a mild allergy. In conclusion, topical ciprofloxacin was effective and well tolerated and would be a particularly useful agent for the treatment of bacterial conjunctivitis and blepharitis.

Comparative Evaluation of Efficacy and Safety of Ciprofloxacin and Norfloxacin Ophthalmic Solutions

The efficacy and safety of ciprofloxacin ophthalmic solution 0.3% and norfloxacin ophthalmic solution 0.3% in the treatment of bacterial conjunctivitis and blepharitis were compared in a double masked randomised study. A total of 131 patients, 65 treated with ciprofloxacin (42 with conjunctivitis and 23 with blepharitis) and 66 treated with norfloxacin (39 with conjunctivitis and 27 with blepharitis) were enrolled in the study at five centres in France. In the efficacy population, pathogens were eradicated or reduced in 96% (24/25) of patients in the ciprofloxacin group and 89% (24/27) in the norfloxacin group. There was no difference between treatments with regard to eradication of particular pathogens. In the efficacy population, clinical cure or improvement was seen in 96% of the patients (24/25 in the ciprofloxacin group and 26/27 in the norfloxacin group). There were no significant differences between ciprofloxacin and norfloxacin with respect to improvements in four symptoms or ten clinical signs. No serious treatment-related adverse events were reported and both ciprofloxacin and norfloxacin were well tolerated.

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.

New therapy option for treatment of methicillin-resistant Staphylococcus aureus keratitis: tigecycline

PURPOSE

The aim of the present study was to evaluate the effectiveness of topically applied tigecycline for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) in a rabbit model.

METHODS

Experimental bacterial keratitis was induced in rabbits by a corneal intrastromal injection of 100 colony-forming units (CFUs) of MRSA bacteria. Sixteen hours after the injection, 28 rabbits were randomly divided into 4 treatment groups of 7 rabbits each. In each group, the rabbits' eyes were treated topically with 19 doses of topical tigecycline (10 or 50 mg/mL), vancomycin (50 mg/mL), or isotonic saline. Slit lamp examinations were performed before and after the inoculation by two observers masked to the study for the determination of clinical severity. Corneas were harvested for bacterial quantitation and histopathologic examination.

RESULTS

No significant differences were observed in the clinical scores between pretreatment and posttreatment in the 4 groups (P>0.05). The mean difference between the pretreatment and posttreatment clinical scores from the 4 treatment groups was also not significant (P>0.05). All treatment groups had significantly lower CFUs compared with the control group. There were no significant differences in the bacterial load among the treatment groups. The minimum inhibitory concentration (MIC) for tigecycline was 0.12 μg/mL, whereas the MIC for vancomycin was 2.2 μg/mL. The tigecycline 10 mg/mL group had the lowest mean epithelial erosion values among the treatment groups.

CONCLUSIONS

Topical tigecycline significantly reduced the bacterial load in infected rabbit corneas and may be as effective as vancomycin for the topical treatment of MRSA keratitis.

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.

Efficacy of besifloxacin in an early treatment model of methicillin-resistant Staphylococcus aureus keratitis

PURPOSE

To determine the effectiveness of topically applied besifloxacin, gatifloxacin, and moxifloxacin for the early treatment of experimental methicillin-resistant Staphylococcus aureus (MRSA) keratitis.

METHODS

Ten hours post-MRSA infection, rabbit eyes were treated topically with 19 doses of phosphate-buffered saline (PBS), besifloxacin, gatifloxacin, or moxifloxacin. Slit-lamp examinations were performed before and after the inoculation. Corneas were harvested for bacterial quantitation and minimal inhibitory concentrations (MICs) were determined.

RESULTS

All 3 fluoroquinolones significantly lowered the clinical severity of the infection as compared to treatment with PBS (P < 0.05). However, the mean log(10) colony-forming unit (CFU) recovered from besifloxacin-treated corneas was significantly lower than all other treatment groups (P < 0.01). CFU recovered from corneas treated with moxifloxacin and PBS showed no significant difference (P = 0.12). Corneas treated with gatifloxacin had a significantly lower log(10) CFU recovered as compared to PBS-treated corneas (P < 0.01). The MICs for gatifloxacin and moxifloxacin were 8 microg/mL, whereas the MIC for besifloxacin was 1 microg/mL.

CONCLUSIONS

All 3 fluoroquinolones significantly lowered the clinical severity of the infection. Besifloxacin had an 8-fold lower MIC for MRSA than gatifloxacin and moxifloxacin, and was significantly more effective than gatifloxacin and moxifloxacin in reducing the number of MRSA in the rabbit cornea.

The inhibitory effect of vancomycin ointment on the manifestation of MRSA keratitis in rabbits

The purpose of this study was to investigate an experimental model of methicillin-resistant Staphylococcus aureus (MRSA) keratitis, and to evaluate the inhibitory effect of vancomycin ointment on the manifestation of keratitis in this model. For the development of the MRSA keratitis model, 16 rabbits received 0.3-ml intrastromal injections of 1 x 10(7) colony forming units/ml MRSA inoculated to each of their corneas. After the MRSA inoculation, the rabbits were examined for a period of 14 days. Vehicle only was applied to each left eye for 2 days as an experimental control. Prototype vancomycin ointments, at concentrations of 0.03%, 0.1%, 0.3%, and 1.0%, were applied to each right eye for 2 days. The treatment commenced immediately after the MRSA inoculation and was administered five times a day at 2-h intervals. Four rabbits were used for each vancomycin ointment concentration. Anterior segments were examined daily, and the minimum inhibitory concentration of vancomycin (percentage in the ointment) for treating MRSA keratitis was determined on day 2. On day 14, no recurrences of infection were observed in the eyes that had not exhibited keratitis on day 2. Forty-eight hours post-inoculation, all left eyes demonstrated severe conjunctivitis, stromal infiltrates at injection sites, and fibroid reactions in the anterior chamber. MRSA keratitis was completely inhibited by 0.3% and 1.0% vancomycin ointments. Although the 0.1% ointment generally could prevent keratitis, punctate infiltrates were found in some eyes. Numerous infiltrates were found in eyes treated with 0.03% ointment. In conclusion, the present study substantiates the view that vancomycin ointment has a potent inhibitory effect upon the manifestations of MRSA keratitis, and indicates that a 0.3% concentration is necessary for effective treatment.

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.

Comparative Efficacy of Topical Moxifloxacin Versus Ciprofloxacin and Vancomycin in the Treatment of P. aeruginosa and Ciprofloxacin-Resistant MRSA Keratitis in Rabbits

PURPOSE

To evaluate the in vivo efficacy of topical moxifloxacin 0.5% versus ciprofloxacin 0.3% in the treatment of Pseudomonas aeruginosa keratitis and topical moxifloxacin 0.5% versus vancomycin 50 mg/mL in the treatment of ciprofloxacin-resistant, methicillin-resistant Staphylococcus aureus (MRSA) keratitis in rabbits.

METHODS

Experimental bacterial keratitis was induced in rabbits by corneal intrastromal injection. Infection proceeded for 12 hours, after which topical antibiotics were applied hourly for 12 hours. Corneal homogenates were plated with serial dilutions for quantitative bacteriology.

RESULTS

Both moxifloxacin and ciprofloxacin performed significantly better than control in the treatment of Pseudomonas aeruginosa keratitis (P=0.0046 and 0.0069, respectively); there were no significant differences between these 2 drugs in bactericidal activity (P=0.1120). Moxifloxacin performed significantly better than control in the treatment of ciprofloxacin-resistant MRSA (P=0.0321) keratitis, and vancomycin showed a trend toward statistical significance in performing better than control (P=0.0576); there were no significant differences between these 2 drugs in bactericidal activity (P=0.5205).

CONCLUSIONS

Topical moxifloxacin 0.5% and ciprofloxacin 0.3% have similar efficacy in the treatment of Pseudomonas aeruginosa keratitis in rabbits. Topical moxifloxacin 0.5% and vancomycin 50 mg/mL have similar efficacy in the treatment of ciprofloxacin-resistant MRSA keratitis in rabbits. These results suggest a potential value for topical moxifloxacin as a broad-spectrum agent in the treatment of bacterial keratitis.

Pseudomonas aeruginosa LasA protease in treatment of experimental staphylococcal keratitis

LasA protease is a staphylolytic endopeptidase secreted by Pseudomonas aeruginosa. We have examined the effectiveness of LasA protease in the treatment of staphylococcal keratitis caused by methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) isolates in a rabbit model. Keratitis was induced by intrastromal injection of the bacteria. The eyes were treated topically, and the efficacy of LasA protease was compared to those of lysostaphin (a staphylolytic protease secreted by Staphylococcus simulans) and vancomycin. When treatment was initiated early (4 h) after infection, practically all of the MSSA- and MRSA-infected corneas were sterilized by LasA protease, and its efficacy in eradicating the bacteria was comparable to those of lysostaphin and vancomycin. By contrast, most of the control corneas were heavily infected, with median values of 4.5 x 10(6) (MSSA) and 5 x 10(5) (MRSA) CFU/cornea (P < 0.001). When treatment was initiated late (10 h) after infection, LasA protease reduced the numbers of CFU in both MSSA- and MRSA-infected corneas by 3 to 4 orders of magnitude compared to the numbers of CFU for the controls (median values, 1,380 and 30 CFU/cornea, respectively, for the treated animals compared to 1.2 x 10(6) and 5 x 10(5) CFU/cornea for the respective controls [P = 0.001]), and it was more effective than vancomycin in eradicating MRSA cells (P = 0.02). In both the early- and the late-treatment protocols, the clinical scores for eyes treated with LasA protease were significantly lower than those for the eyes of the corresponding controls and comparable to those for the lysostaphin- and vancomycin-treated eyes. We conclude that LasA protease is effective in the treatment of experimental S. aureus keratitis in rabbits and may have potential for the treatment of disease in humans.

Effectiveness of mupirocin and polymyxin B in experimental Staphylococcus aureus, Pseudomonas aeruginosa, and Serratia marcescens keratitis

PURPOSE

The purpose of this study was to determine the effectiveness of mupirocin and polymyxin B, alone and in combination, in vitro and in vivo using rabbit models of, and keratitis.

METHODS

Rabbit eyes were intrastromally injected with 1,000 colony-forming units (CFUs) of or or 100 CFUs of Rabbits were then treated with 2.7 mg/mL mupirocin, 10,000 U/mL polymyxin B, a mupirocin:polymyxin B combination, or 0.3% ciprofloxacin. Vehicle and untreated controls were also included. Treatment schedules depended on the strain injected. The number of CFUs was determined for all eyes after treatment.

RESULTS

The mupirocin:polymyxin B combination was effective for all three genera both in vitro and in vivo. For keratitis, the mupirocin:polymyxin B combination was more effective than either drug alone and significantly reduced the log number of bacteria in the cornea by more than 3 logs compared with the vehicle or untreated controls (p <or= 0.0016). For, the mupirocin:polymyxin B combination treatment significantly reduced the number of CFUs per cornea relative to the individual drugs, vehicle, or untreated controls (p <or= 0.016). For, the mupirocin:polymyxin B combination therapy significantly reduced the number of bacteria in rabbit corneas relative to the individual drugs, vehicle, or untreated groups (p <or= 0.0001). Therapy with the mupirocin:polymyxin B combination was equivalent to ciprofloxacin therapy (p = 0.80).

CONCLUSION

The mupirocin:polymyxin B combination was effective in treating experimental, and keratitis.

The evolution of antibiotic therapy for bacterial conjunctivitis and keratitis: 1970-2000

The editors of this Festschrift asked us to review the use of antibiotics for the treatment of bacterial conjunctivitis and keratitis over the past 25 years, a period coinciding with the life of the Castroviejo Corneal Society. We believe it is more appropriate to begin our review in the late 1960s. about the time that experimental and clinical studies and algorithms for the clinical care derived from these studies helped shape a more rigorous approach to therapy. Those years saw the introduction of antibiotics that were adapted for ophthalmic use, many of which are still being used today. We will give more weight to our review of keratitis than conjunctivitis.

The effectiveness of a topical antibiotic irrigating solution in a model of staphylococcal keratitis after lamellar keratectomy

PURPOSE

To create a model of Staphylococcus aureus keratitis after lamellar keratectomy; to assess the toxicity of an antibiotic irrigating solution on the corneal stromal bed; and to test the chemotherapeutic effectiveness of a topical antibiotic, both alone and with an antibiotic-containing irrigating solution in preventing S. aureus keratitis after lamellar keratectomy.

METHODS

The right eye of each of 38 rabbits were used in this study. In 18 eyes, a lamellar flap was created with a microkeratome, and an inoculum of S. aureus (either 1,000, 5,000, or 50,000 CFUs) was instilled under each flap; the eyes were examined for signs of infection and inflammation at 24 and 48 hours. In another five eyes, a lamellar flap was created in the same manner and the stromal bed was irrigated with 0.3% ofloxacin; the eyes were assessed for ocular inflammatory changes and evidence of crystalline deposits. Finally, in each of 15 additional eyes, 1,000 CFUs of S. aureus were instilled under a lamellar flap to create experimental infectious keratitis. The keratitis was treated according to three regimens: irrigation of the stromal bed with sterile balanced salt solution; irrigation of the stromal bed with 0.3% ofloxacin, followed by application of topical ofloxacin four times a day; application of topical ofloxacin only, four times a day. Eyes were examined for infection and ocular inflammatory changes at 24 and 48 hours.

RESULTS

Staphylococcus aureus keratitis can consistently be produced under the stromal flap by inoculation of relatively few organisms. Irrigation of the stromal bed with commercial-strength topical ofloxacin does not appear to be toxic to the stromal bed, with no evidence of crystalline precipitates of the antibiotic. In our model of infectious keratitis after lamellar keratectomy, both topical ofloxacin alone and the combination of topical ofloxacin and irrigation of the stromal bed with 0.3% ofloxacin were effective at preventing S. aureus keratitis. However, the combined treatment of antibiotic irrigation plus topical antibiotic was more effective at preventing inflammation than topical ofloxacin alone.

CONCLUSIONS

In this model of S. aureus keratitis after lamellar keratectomy, irrigation of the stromal bed with antibiotic plus topical antibiotic appears to be both safe and effective for preventing infection.

Specific roles of alpha-toxin and beta-toxin during Staphylococcus aureus corneal infection

Staphylococcus aureus corneal infection results in extensive inflammation and tissue damage. Our previous studies of bacterial mutants have demonstrated a role for alpha-toxin in corneal virulence. This study analyzes, by genetic rescue experiments, the virulence of mutants affecting alpha-toxin and beta-toxin activity and demonstrates the ocular toxicity of these purified staphylococcal proteins. Three types of isogenic mutants were analyzed: (i) mutants specifically deficient in alpha-toxin (Hla) or beta-toxin (Hlb), (ii) a mutant deficient in both Hla and Hlb, and (iii) a regulatory mutant, deficient in the accessory gene regulator (agr), that produces reduced quantities of multiple exoproteins, including alpha- and beta-toxins. Plasmids coding for Hla and Hlb (pDU1212 and pCU1hlb, respectively) were used to restore toxin activity to mutants specifically deficient in each of these toxins. Either corneas were injected intrastromally with logarithmic-phase S. aureus or purified alpha- or beta-toxins were administered to normal eyes. Ocular pathology was evaluated by slit lamp examination and myeloperoxidase activity of infiltrating polymorphonuclear leukocytes. Corneal homogenates were cultured to determine the CFU per cornea. Eyes infected with the wild-type strain developed significantly greater corneal damage than eyes infected with Agr-, Hlb-, or Hla- strains. Epithelial erosions produced by parent strains were not produced by Agr- or Hla- strains. Hlb+ strains, unlike Hlb- strains, caused scleral edema. Plasmid pDU1212 restored corneal virulence to strain DU1090 (Hla-), and plasmid pCU1hlb restored corneal virulence to strain DU5719 (Hlb-). Application of purified alpha-toxin produced corneal epithelial erosions and iritis, while application of beta-toxin caused scleral inflammation. These studies confirm the role of alpha-toxin as a major virulence factor during S. aureus keratitis and implicate beta-toxin, a mediator of edema, as a lesser contributor to ocular damage.

Efficacy of tobramycin drops applied to collagen shields for experimental staphylococcal keratitis

Treatment of staphylococcal keratitis includes tobramycin drops at repeated intervals, a prolonged therapy that is disruptive to the patient. To identify a regimen involving less frequent drug application, we compared the efficacy of fortified tobramycin (1.36%) administered by collagen shields or in topical drop form to rabbit corneas intrastromally infected with staphylococci. Eyes were treated with shields hydrated in and supplemented with fortified tobramycin drops (1.36%) applied every 1, 2, 5, or 10 h, from 10 to 20 h postinfection. For topical drop treatment alone, tobramycin was applied following the identical regimen. Untreated corneas contained 10(6) colony forming units. Shields supplemented with tobramycin drops applied every 1, 2, or 5 h sterilized 100% of the corneas. Shields supplemented with tobramycin drops applied at 10 h sterilized 58% of the corneas. Topical delivery of tobramycin every h sterilized all corneas; drops alone applied at longer intervals, such as 2, 5, or 10 h, sterilized 83%, 17%, and 0% of the corneas, respectively. Collagen shield delivery of tobramycin with supplemental topical drops can eradicate staphylococci in this model with less frequent dosing intervals than are required with topical therapy alone.

Pharmacokinetic considerations in the treatment of bacterial keratitis

The eye is relatively impermeable to micro-organisms and other environmental elements. However, if corneal integrity is breached by trauma, a sight-threatening bacterial infection can result. Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus pneumoniae are the most common bacterial pathogens associated with infection of compromised corneas. Bacterial enzymes and toxins, as well as factors associated with the host immune response, can lead to tissue destruction during corneal infection. For successful therapy, an antibacterial agent must be active against the pathogen and must be able to overcome the permeability barrier of the cornea. Topical application of antibacterial agents adequately delivers drugs to the cornea and aqueous humour. However, drug concentrations at the site of infection are not always sufficient to rapidly kill infective organisms. Infections with antibiotic-resistant strains present an even greater therapeutic challenge. In addition, sterilisation of the cornea by antibacterial agents does not eliminate inflammation and corneal scarring that accompany infection. Steroidal and non-steroidal antiinflammatory agents limit corneal scarring during experimentally induced bacterial keratitis. However, although promising, concomitant use of these drugs with antibacterial agents remains controversial. Two ocular drug delivery systems that provide high and sustained concentrations of drug to ocular tissues are corneal collagen shields and transcorneal iontophoresis. The collagen shield, originally designed as a bandage lens, prolongs drug contact with the cornea. Chemotherapeutic studies of experimental bacterial keratitis demonstrate that shields hydrated with antibacterial agents reduce bacteria in the cornea as well as or better than frequent applications of fortified antibacterial drops. Transcorneal iontophoresis uses an electric current to drive charged drugs into the cornea. In experimentally induced bacterial keratitis, transcorneal iontophoresis of antibacterial agents is superior to topically administered ocular drops for reducing the numbers of bacteria in the cornea. Although both drug delivery systems appear to be well tolerated and nontoxic in animal models, clinical trials in patients are required to determine the usefulness of these drug delivery systems in clinical trials. Based on present experimental results, future therapy of bacterial keratitis will involve efficient drug delivery devices, the use of new antibacterial agents or combinations of presently available antibacterial agents, and careful use of adjuvant anti-inflammatory agents.

Corneal virulence of Staphylococcus aureus: roles of alpha-toxin and protein A in pathogenesis

Staphylococcus aureus produces a variety of proteins, including alpha-toxin and protein A, that could contribute to corneal tissue damage during keratitis. We examined corneal infections produced by intrastromal injection of four S. aureus strains--three isogenic mutants, one lacking alpha-toxin (Hly- Spa+), one lacking protein A (Hly+ Spa-), and one lacking both alpha-toxin and protein A (Hly- Spa-), and the wild type (Hly+ Spa+)--in a rabbit model of experimental keratitis. Rabbit corneas were injected intrastromally with 100 CFU of one of the four strains, and the eyes were examined by slit lamp biomicroscopy over a 25-h period. Corneal homogenates were used for determination of CFU and neutrophil myeloperoxidase activity at 5-h intervals. All strains had the same logarithmic growth curve from 0 to 10 h postinfection, after which CFU remained constant at 10(7) CFU per cornea. By 15 h postinfection, slit lamp examination scores were significantly higher for eyes infected with Hly+ strains than for Hly(-)-infected eyes. At this time, distinct epithelial erosions were seen in Hly(+)-infected eyes but not in Hly(-)-infected eyes. Myeloperoxidase activity was significantly greater for Hly(+)-infected corneas than for Hly(-)-infected corneas at both 20 and 25 h postinfection. Spa(+)- and Spa(-)-infected eyes showed no differences in slit lamp examination scores or myeloperoxidase activities. These results suggest that alpha-toxin, but not protein A, is a major virulence factor in staphylococcal keratitis, mediating the destruction of corneal tissue in eyes infected with this bacterial pathogen.

Ciprofloxacin. A review of its pharmacological profile and therapeutic use in the elderly

Ciprofloxacin belongs to the fluoroquinolone class of antimicrobial agents which primarily inhibit bacterial DNA gyrase. It is effective after oral or intravenous administration, demonstrating potent antibacterial activity against most Gram-negative, and many Gram-positive bacteria. Although most bacterial strains have remained susceptible to the drug, low rates of resistance have been observed in some strains of Pseudomonas aeruginosa and enterococci and higher rates in methicillin-resistant Staphylococcus aureus. Ciprofloxacin attains concentrations in most tissues and body fluids sufficient to inhibit the majority of susceptible pathogens. Its pharmacokinetic profile in the elderly (> or = 65 years) is broadly similar to that reported in younger persons, although plasma concentrations are higher, and renal clearance is decreased in elderly persons. Ciprofloxacin is an effective treatment for those infections most common in elderly patients, including infections of the urinary tract, lower respiratory tract, skin and soft-tissues, and bone and joints, and is an effective agent for prophylaxis in transurethral surgery. Orally administered ciprofloxacin appeared to be at least as effective as alternative orally administered antimicrobial agents (trimethoprim, cotrimoxazole [trimethoprim/sulfamethoxazole], amoxicillin, amoxicillin/clavulanic acid) and also as effective as various parenteral agents (ceftriaxone, cefamandole, ceftazidime, cefotaxime) in a small number of comparative clinical trials. However, further studies are needed to clarify the comparative efficacy of ciprofloxacin with that of other oral and parenteral agents in the elderly. Initial trials have also indicated therapeutic efficacy of oral ciprofloxacin in malignant external otitis and bacterial prostatitis. Nevertheless, with its good tolerability profile and potent antimicrobial activity following oral administration, ciprofloxacin appears to offer a valuable alternative for treating various acute and chronic infections in elderly patients. Causative pathogens are frequently multiresistant in this patient group, and ciprofloxacin avoids or minimises the need for parenteral therapy.