In the last few years, the genus Nocardia has undergone rapid taxonomic expansion due to the utilization of 16S sequencing1 resulting in more than 100 recognized described species, although around two thirds of them are known as pathogen.2
Nocardia infections can be acquired by either inhalation, causing lung disease in immunocompromised patients3 or traumatic inoculation. Ocular affectation caused by these organisms is a rare location, being keratitis more frequent than scleritis or endophthalmitis infection.4 Here we describe one case of side-port infection of a self-sealing corneal tunnel incision following an uneventful phacoemulsification as a complication of cataract surgery due to Nocardia nova.
The patient was a 59-year-old male who underwent an uneventful clear corneal temporal incision phacoemulsification with a foldable intraocular lens (day 0). He recovered uneventfully a month after surgery (day 30) being treated with a combination of tobramycin/dexamethasone and diclofenac eye drops.
In the 48 day, the patient came to the hospital with complaints of redness, tearing, photophobia, blurry vision and irritation in the right eye during two days. Visual acuity was recorded as 20/30. The cornea showed a small stromal infiltrate of 3mm diameter in the superior temporal quadrant of the right cornea with a 1+ anterior chamber reaction but no hypopyon, being 1mm from the limbus (in the self-sealing tunnel incision), with an epithelial defect of 2mm diameter, an ill-defined border and mild surrounding corneal edema (Fig. 1). Corneal scraping was taken for microbiological processing and inoculated on tryptic soy 5% sheep blood agar and chocolate agar (bioMérieux®, Marcy-L¿Étoile, France), being incubated at 37°C in 5% CO2 aerobic atmosphere. He was empirically treated with hourly fortified vancomycin and ceftazidime eye drops. On follow-up the infiltrate did not improve.
After 3 days of incubation (day 51), the culture revealed a significant growth of a microorganism. The Gram-stain of the colony showed gram positive branching filamentous rods. A Ziehl–Neelsen stain and a modified Ziehl–Neelsen stain (5% sulfuric acid) were performed, being negative and positive respectively. The organism was identified as Nocardia spp. according to the morphology of the colony and the stain characteristics. The patient had not any risk factors for this infection and he did not travel abroad. Then, treatment was changed to oral trimethoprim–sulfamethoxazole (400/80mg twice daily) and hourly fortified amikacin and moxifloxacin 0.5% eye drops. In the day 53 clinical improvement was obvious.
Due to partial resolution of the infiltrate, oral cotrimoxazole treatment was finished in day 61, and topical treatment with amikacin and moxifloxacin was finally stopped in day 77 because the lesion was finally cured.
An antimicrobial susceptibility test was performed (day 51) through broth microdilution test (Sensititre®, Trek Diagnostics Systems, West Sussex, England). Minimum inhibitory concentration (MIC) (μg/ml) values were obtained after 72h of incubation (day 54) and they were as follows: susceptible to amikacin (<1) and cotrimoxazole (2); and resistant to ciprofloxacin (>4) and moxifloxacin (4).
Despite “in vitro” resistant to quinolones, topical moxifloxacin treatment was maintained due to the improvement of the patient.
The strain was then submitted to Instituto de Salud Carlos III (Majadahonda, Madrid, Spain) (day 55) for 16S rRNA gene sequencing, being identified as Nocardia nova (day 85).
Keratitis is an ocular infection affecting the cornea, with unusual reported cases due to Nocardia or Mycobacterium.5
The most effective agents toward most infections produced by Nocardia are cotrimoxazole and amikacin, being the latter the treatment of choice for Nocardia keratitis.6 Other drugs that can be used are tetracycline, chloramphenicol and fluoroquinolones.4 According to a paper developed in our country, all strains of Nocardia nova are susceptible to amikacin and cotrimoxazole, whereas almost all of them are resistant to fluoroquinolones.5 However, moxifloxacin shows a minimum susceptibility7 and its concentration in cornea are high,8 which could be the reason why “in vitro” resistant is not always related to a failure treatment of keratitis.
Among the eye infections, there are few cases of conjunctivitis9 and scleritis10 due to Nocardia nova complex. Here we describe the first case of keratitis due to Nocardia nova secondary to ocular surgery, with a good outcome after prolonged therapy, despite in vitro quinolone resistance.
We acknowledge to Instituto de Salud Carlos III (Majadahonda, Madrid, Spain) for definitive identification of the strain.
