Comparison of topical antibiotics for treating Mycobacterium chelonae keratitis in a rabbit model

Atypical microbial keratitis

Atypical microbial keratitis refers to corneal infections caused by micro-organisms not commonly encountered in clinical practice. Unlike infections caused by common bacteria, cases of atypical microbial keratitis are often associated with worse clinical outcomes and visual prognosis. This is due to the challenges in the identification of causative organisms with standard diagnostic techniques, resulting in delays in the initiation of appropriate therapies. Furthermore, due to the comparatively lower incidence of atypical microbial keratitis, there is limited literature on effective management strategies for some of these difficult to manage corneal infections. This review highlights the current management and available evidence of atypical microbial keratitis, focusing on atypical mycobacteria keratitis, nocardia keratitis, achromobacter keratitis, and pythium keratitis. It will also describe the management of two uncommonly encountered conditions, infectious crystalline keratopathy and post-refractive infectious keratitis. This review can be used as a guide for clinicians managing patients with such challenging corneal infections.

Treatment-Resistant Bacterial Keratitis: Challenges and Solutions

Bacterial keratitis is an important ophthalmic emergency and one of the most common causes of corneal blindness. The main causes of treatment resistance in bacterial keratitis are failure to eliminate predisposing factors, misdiagnosis and mistreatment. At first, exogenous, local and systemic predisposing factors that disturbing ocular surface must be eliminated to improve corneal ulcers and to prevent recurrences. Smears and scrapings for staining and culture are indispensable diagnostic tools for cases of sight-threatening keratitis (centrally located, multifocal, characterized by melting, painful). Main treatment agents in bacterial keratitis treatment are topical antibiotics. Until the results of culture antibiograms reach the ophthalmologist, empirical antibiotic selections based on direct microscopic examination and gram stain findings are the most appropriate initial treatment approach currently. S. aureus and coagulase-negative staphylococci (CoNS), the most common gram-positive agents, have resistance rates of more than 30% for fluoroquinolone and methicillin. Multidrug resistance rates are similarly high in these microorganisms. P. aeruginosa is the most common gram-negative micro-organism, in case of multidrug-resistant isolates, both functional and anatomical prognosis of the eyes are very poor. In cases of sight-threatening and resistant keratitis, antibiotic susceptibility testing containing imipenem, colistin, and linezolid is seeming to be an important requirement. Despite its efficiency limited to superficial cases, a nonpharmaceutical anti-infective treatment option such as corneal crosslinking for bacterial keratitis is an emerging hope, while antibiotic resistance increases.

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Use of Topical Besifloxacin in the Treatment of Mycobacterium chelonae Ocular Surface Infections

PURPOSE

To present the clinical outcome of 3 cases of ocular surface infections by Mycobacterium chelonae treated with besifloxacin (0.6%, Besivance; Bausch & Lomb, Tampa, FL).

METHODS

In this retrospective review of a small case series, we reviewed the medical records of 3 clinical patients with M. chelonae infection involving the ocular surface. Besifloxacin was used as an adjunct in 2 cases of keratitis and as the principal therapeutic agent in a case of nodular conjunctivitis.

RESULTS

Two patients who presented with culture-proven M. chelonae keratitis initially had been treated with topical amikacin and oral clarithromycin for 6 months in the first case and for 2 months in the second without complete resolution. Topical besifloxacin was added as an adjunct therapy to amikacin with progressive weaning of clarithromycin. Both cases of keratitis eventually resolved without recurrence after discontinuation of topical amikacin and besifloxacin. A third patient presented with nodular conjunctival inflammation, which initially had been treated with topical ciprofloxacin and corticosteroids without improvement. One nodular lesion was excised and submitted for microbial culture, which revealed the growth of M. chelonae. Marked improvement of the conjunctivitis was noted after 3 weeks of treatment with topical besifloxacin. Complete resolution of the conjunctival nodules was achieved after 10 weeks of treatment with besifloxacin.

CONCLUSIONS

Topical besifloxacin seems to be a useful adjunct agent in the treatment of nontuberculous mycobacterial keratitis by M. chelonae and may be viable for use as a first-line agent in cases of nodular conjunctivitis by M. chelonae.

Non-tuberculous mycobacterial keratitis

Non-tuberculous mycobacteria are environmental, opportunistic pathogens that are increasingly being recognized as important causes of many human diseases. Among them, rapidly growing mycobacteria are the most notorious organisms causing infectious keratitis. Non-tuberculous mycobacterial (NTM) keratitis commonly occurs after trauma or refractive surgery, and can masquerade as fungal, herpetic or amoebic keratitis. Therefore, the diagnosis is often delayed. Prolonged medical treatment and judicious surgical debridement are required in order to eradicate the pathogens. Combination therapy with aminoglycosides, macrolides and fluoroquinolones improves the prognosis and decreases the occurrence of drug resistance. However, regardless of the development of new diagnostic techniques and antimicrobials, NTM keratitis remains a clinical challenge for most ophthalmologists. In this article, we provide a concise introduction to the epidemiological features and clinical characteristics of NTM keratitis, and the modern diagnostic tools used for it. We also summarize the current concepts of prevention and treatment for this potentially devastating condition.

Effectiveness of fluoroquinolones against Mycobacterium abscessus in vivo

PURPOSE

To determine the effectiveness of fluoroquinolones against Mycobacterium abscessus in vivo.

METHODS

M. abscessus growth was determined quantitatively in rabbit corneas after intrastromal bacterial injection (10(4) CFU/cornea; n >or= 4 corneas per group). Eyes were treated topically with 0.3% ciprofloxacin, 0.5% levofloxacin, or 0.5% moxifloxacin by three protocols: (1) 1 drop of antibiotic applied hourly for 10 hr on day 3 postinfection (PI); (2) 1 drop applied every 2 hr for 10 hr on days 2 and 3 PI; or (3) 1 drop applied every 2 hr for 10 hr on days 1, 2, and 3 PI. Corneas were cultured 1 hr after the last topical drop. Results are expressed as the log CFU.

RESULTS

Bacteria in control group reached maximal numbers in vivo by day 3 PI (approximately 6 logs CFU/cornea). Treatment of infected eyes on day 3 with moxifloxacin or levofloxacin resulted in approximately 2.0 log decrease in CFU/cornea relative to the untreated control. Treatment on days 2 and 3 with moxifloxacin or levofloxacin resulted in approximately 3.0 and 2.5 log CFU/cornea decrease, respectively. Ciprofloxacin had no effect on bacterial load. Treatment on days 1, 2, and 3 with moxifloxacin resulted in a 5.5 log CFU decrease, whereas treatment with levofloxacin or ciprofloxacin resulted in a approximately 4.0 log CFU decrease.

CONCLUSIONS

Moxifloxacin, and to a lesser extent levofloxacin and ciprofloxacin, demonstrated significant effectiveness for reducing the number of M. abscessus in vivo, suggesting the potential usage of these agents in prevention of M. abscessus keratitis.

In Vitro Activity of Fluoroquinolones Against Mycobacterium abscessus and Mycobacterium chelonae Causing Infectious Keratitis After LASIK in Brazil

PURPOSE

To evaluate the in vitro activity of fluoroquinolones against Mycobacterium abscessus and Mycobacterium chelonae isolated from outbreaks of infectious keratitis in Brazil.

MATERIAL AND METHODS

Micobacterial isolates were recovered from infectious keratitis cases related outbreaks that occurred in Brazil after LASIK for myopia. Two outbreaks occurred in Rio de Janeiro in 1998 and 1999, and 3 in São Paulo between 2000 and 2003. All laboratorial analysis, including molecular identification and antibiotic susceptibility testing with determination of the minimum inhibitory concentration (MIC) levels for ciprofloxacin, ofloxacin, gatifloxacin, and moxifloxacin, were performed at Universidade Federal de São Paulo in Brazil.

RESULTS

Fifteen samples were identified as M. chelonae, and 3 were identified as M. abscessus. The outbreaks studied were designated SP-1 in 2000; SP-2 in 2000-2001; and SP-3 in 2003, R1 in 1988 and R2 in 1999. All but 1 of the M. chelonae were resistant to all fluoroquinolones with an MIC90 greater than 32 microg/mL. The only susceptible isolate had MIC levels for ciprofloxacin, ofloxacin, gatifloxacin, and moxifloxacin of 0.38 microg/mL, 0.032 microg/mL, 0.047 microg/mL, and 0.19 microg/mL, respectively. MIC levels for all 3 M. abscessus isolates tested were greater then 32 microg/mL for all fluoroquinolones tested.

CONCLUSIONS

Fluoroquinolone MICs for 17 M. abscessus and M. chelonae isolates recovered from infectious keratitis cases in Brazil indicate that they are not susceptible to these drugs in vitro. Further studies to investigate the in vivo effectiveness of fluoroquinolones against mycobacteria are required because in vitro tests do not support their use in the treatment of micobacterial keratitis in this particular geographic area.

Mycobacterium chelonae Keratitis

PURPOSE

To describe the microbiologic diagnosis of putative Mycobacterium chelonae keratitis in a soft contact lens wearer by initial evaluation of Gram- and Kinyoun (acid fast)-stained smears of fluid from patient's contact lens care system.

METHODS

Corneal ulcer of suspected Acanthamoeba etiology developed in a 28-year-old soft contact lens wearer. After corneal scrapings were negative, microbiologic consultation led to evaluation of stained smears and culture of fluid from patient's contact lens care system.

RESULTS

Gram stain of smears showed a polymicrobic flora distinguished by numerous gram-positive, beaded, tightly banded, "diphtheroid-like" bacilli strongly suggestive of a rapidly growing mycobacterial species. Kinyoun-stained smears revealed innumerable acid-fast bacilli singly and in tightly woven bundles (cords), which culturally proved to be M. chelonae. Treatment with ciprofloxacin and amikacin resolved the ulcer.

CONCLUSION

Diagnosis of M. chelonae keratitis in contact lens wearers is often delayed or even overlooked. Additionally, in the absence of overt corneal injury, eg, trauma or surgery, a source for the infecting mycobacterial species in the setting of contact lens wear has not been identified. If searched for, however, as in the present case, the patient's contact lens care system may serve as the reservoir for the microorganism. Staining for acid-fast bacilli is further recommended when smears of contact lens care solution of a patient with a corneal ulcer shows the presence of gram-positive "diphtheroid-like" organisms.

An experimental model of mycobacterial infection under corneal flaps

In order to develop a new experimental animal model of infection with Mycobacterium chelonae in keratomileusis, we conducted a double-blind prospective study on 24 adult male New Zealand rabbits. One eye of each rabbit was submitted to automatic lamellar keratotomy with the automatic corneal shaper under general anesthesia. Eyes were immunosuppressed by a single local injection of methyl prednisolone. Twelve animals were inoculated into the keratomileusis interface with 1 microl of 10(6) heat-inactivated bacteria (heat-inactivated inoculum controls) and 12 with 1 microl of 10(6) live bacteria. Trimethoprim drops (0.1%, w/v) were used as prophylaxis for the surgical procedure every 4 h (50 microl, qid). Animals were examined by 2 observers under a slit lamp on the 1st, 3rd, 5th, 7th, 11th, 16th, and 23rd postoperative days. Slit lamp photographs were taken to document clinical signs. Animals were sacrificed when corneal disease was detected and corneal samples were taken for microbiological analysis. Eleven of 12 experimental rabbits developed corneal disease, and M. chelonae could be isolated from nine rabbits. Eleven of the 12 controls receiving a heat-inactivated inoculum did not develop corneal disease. M. chelonae was not isolated from any of the control rabbits receiving a heat-inactivated inoculum, or from the healthy cornea of control rabbits. Corneal infection by M. chelonae was successfully induced in rabbits submitted to keratomileusis. To our knowledge, this is the first animal model of M. chelonae infection following corneal flaps for refractive surgery to be described in the literature and can be used for the analysis of therapeutic responses.

Therapeutic penetrating keratoplasty for microbial keratitis in Taiwan from 1987 to 2001

PURPOSE

To determine the surgical outcomes of therapeutic penetrating keratoplasty (PKP) and its role in the management of microbial keratitis.

DESIGN

Interventional case series.

METHODS

We retrospectively performed a chart review of the hospital records of all 151 patients undergoing therapeutic PKP for culture-proven microbial keratitis at the National Taiwan University Hospital during a 14 year-period (1987-2001). Patients were divided into three categories: (1) bacterial keratitis; (2) fungal keratitis; and (3) acanthamoebic keratitis. Each of the following criteria was evaluated: (1) graft clarity 1 month and 1 year postoperatively; (2) cure of the disease; and (3) anatomical success rate.

RESULTS

A total of 108 therapeutic PKP met the criteria. Therapeutic PKP eradicated the infection in 37/41 of patients with bacterial keratitis, 36/52 of patients with fungal keratitis, and 13/15 of patients with acanthamoebic keratitis. 22/32 of grafts of bacterial keratitis, 20/39 of fungal keratitis, and 11/14 of acanthamoebic keratitis remained clear at 1 year postoperatively. A higher percentage of graft clarity at 1 year postoperatively was achieved in all three categories when grafts were 8.5 mm or less compared with larger grafts. All five patients with secondary endophthalmitis observed at the time of therapeutic PKP experienced a progression of infection despite aggressive surgical treatment, and had to be enucleated.

CONCLUSIONS

Therapeutic PKP is valuable in the management of microbial keratitis that is unresponsive to medical therapy. A higher percentage of clear graft was found when grafts were smaller in all three categories. Surgical results are worse for patients with fungal keratitis, regardless of graft clarity, anatomical success, or infection eradication rate.

Rapid diagnosis and treatment of mycobacterial keratitis after laser in situ keratomileusis

We report the results of laser in situ keratomileusis (LASIK) in a 51-year-old woman with subsequent mycobacterial keratitis diagnosed by staining with acid-fast and fluorochrome methods, a technique known to have good sensitivity and specificity for mycobacteria. A rapid diagnosis was made without waiting for cultures, and treatment was instituted, including tapering of topical steroids and appropriate antibiotic therapy. The result was preservation of the LASIK flap and a favorable visual outcome at 6 months.

An outbreak of Mycobacterium chelonae infection after LASIK

OBJECTIVE

To describe an outbreak of mycobacterial keratitis after laser in situ keratomileusis (LASIK), including the microbiologic investigation, clinical findings, treatment response, and outcome.

DESIGN

Retrospective, noncomparative, interventional case series.

PARTICIPANTS

Patients (n = 10) who underwent LASIK surgery between August 22 and September 4, 2000, and developed mycobacterial infection.

METHODS

Patients were prospectively followed in relation to microbiologic investigation, clinical findings, treatment response, and outcome.

MAIN OUTCOME MEASURES

Most patients underwent bilateral simultaneous LASIK. Postoperative infection was signaled by the appearance of corneal infiltrates in the third postoperative week. The microbiologic workup was performed on cultures obtained either by direct scraping of the cornea or by lifting the flap. Medical therapy was instituted based on drug susceptibility testing. Surgical interventions such as corneal debridement and flap removal were performed during recurrences or when there was no satisfactory clinical response.

RESULTS

Cultures revealed Mycobacterium subspecies chelonae. Patients were treated with topical clarithromycin (1%), tobramycin (1.4%), and ofloxacin (0.3%). Oral clarithromycin (500 mg twice a day) was prescribed for those patients who did not respond clinically to topical treatment. Four eyes healed on this regimen. Flap removal was necessary in seven eyes.

CONCLUSIONS

This report highlights mycobacteria as an etiologic infectious agent after LASIK. Diagnosis can be difficult and is often delayed. The treatment mainstay is prolonged antibiotic therapy. Surgical debridement and flap removal may shorten the disease course.

Infectious post-LASIK crystalline keratopathy caused by nontuberculous mycobacteria

PURPOSE

To report three cases of infectious crystalline keratopathy caused by non-tuberculous mycobacteria after LASIK surgery.

METHODS

Interventional case reports and literature review.

RESULTS

Infectious keratitis with clinical features of crystalline keratopathy after LASIK is described. Culture revealed Mycobacterium chelonae from the corneal scrapings of the three patients, all of whom underwent medical and surgical (debridement) treatment.

CONCLUSIONS

Mycobacteria may cause infectious crystalline keratopathy after LASIK. The presence of crystalline keratopathy in patients that underwent LASIK must be considered an indicator of nontuberculous mycobacteria infection. Microbiologic work-up of a corneal specimen is required for the institution of appropriate therapy.

Mycobacterial Infections of the Head and Neck

Mycobacteria are important causes of head and neck infections. Mycobacterial lymphadenitis may be caused by both Mycobacterium tuberculosis and a variety of nontuberculous myocbacteria. Changes in the epidemiology of tuberculosis have caused a shift of the peak age range of tuberculous lymphadenitis from childhood to ages 20 to 40 years. Short-course chemotherapy is highly effective. Mycobacterium avium has become the most common cause of nontuberculous lymphadenitis, but new mycobacterial species are increasingly recognized. Treatment consists primarily of complete surgical excision, although roles for antimycobacterial chemotherapy are being identified. Transient flares of mycobacterial lymphadenitis, which occur during initiation of antituberculous therapy and in HIV-infected patients after initiation of antiretroviral therapy, may respond to short courses of corticosteroids. Tuberculous otitis media has become uncommon. Otitis media due to nontuberculous mycobacterial infection is increasingly seen in patients with pre-existing ear disease and after surgical and otic interventions. Tuberculosis of the eye has also become uncommon but may occur via hematogenous dissemination or direct innoculation. Nontuberculous mycobacteria, most commonly Mycobacterium chelonae and Mycobacterium fortuitum, may cause keratitis, usually after some form of corneal trauma.