Current diagnostic tools and management modalities of Nocardia keratitis

A complex case of Nocardia keratitis: challenges in diagnosis and therapy

Nocardia keratitis is a rare cause of microbial keratitis, primarily affecting patients in tropical and subtropical regions. Its diagnostic challenge arises from this keratitis uncommon presentation, which often mimics other infectious keratitis types, leading to delays in appropriate treatment. This case report aims to elucidate the complexities of diagnosing and managing Nocardia keratitis of a 41-year-old male who had a chronic, progressively worsening wreath-pattern corneal infiltrate and hypopyon following ocular trauma. Initial empirical treatments were ineffective. Diagnostic confirmation via corneal scraping culture enabled targeted antimicrobial therapy. Subconjunctival amikacin and topical tobramycin led to gradual improvement, though complications such as corneal scarring and neovascularization remained, indicating potential need for surgical intervention. This case emphasizes the importance of high clinical suspicion and precise laboratory diagnostics in managing rare cases of Nocardia keratitis. Establishing standardized treatment guidelines for rare ocular infections could improve clinical outcomes.

[Bacterial keratitis: Retrospective and prospective 2024]

Bacterial keratitis (BK) is an infection of the cornea caused by one or more bacteria. Contact lens wear is the main risk factor. Staphylococcus and Pseudomonas are the most frequently isolated pathogens in developed countries. BK requires a standardized work-up to avoid diagnostic and therapeutic delays that may negatively affect visual prognosis. Corneal signs, the speed at which lesions progress and the presence of risk factors allow the clinician to presume an empirical microbiological diagnosis, but corneal scraping, which allows the isolation and identification of the bacteria involved in the infection, is the only way to confirm the diagnosis. The type of antibiotic treatment depends on the severity of the lesions, the risk factors involved, and the bacteria identified. Corticosteroids have been shown to be effective as adjuvant therapy and may be used under certain well-defined circumstances. Surgical treatment is sometimes necessary.

Clinical perspective and outcome of culture-negative microbial keratitis: A retrospective study

PURPOSE

To study the risk factors, clinical features, and treatment outcomes of patients with culture-negative keratitis (CNK).

METHODS

A retrospective data review of 933 patients with CNK was performed from January 2018 to December 2020. The variables such as the history of injury, visual acuity, slit-lamp findings with measurements of size and depth of ulcer, microbiological evaluation, duct patency, blood glucose levels, and treatment were considered, and clinical outcome was analyzed.

RESULTS

Of the 933 patients with CNK, 763 (81.8%) were medically managed, with a mean treatment duration of 2.08 ± 1.7 weeks. Among them, 622 (66.7%) were both smear and culture-negative, and 311 (33.3%) showed only smear positivity. Smear-positive patients showed a positive correlation with the history of injury. A higher incidence of fungal growth on repeat culture was observed. Surgical interventions were done only in 18.2% of the patients; the rest were treated with topical medications alone.

CONCLUSION

High clinical suspicion, differentiation of causative organisms based on clinical findings, and initiating empirical therapy with broad-spectrum antibiotics and antifungals improve the ultimate prognosis in patients with CNK, even though a standard protocol for empirical medical treatment may differ among institutions and surgeons based on their clinical experience and geographical variations.

Disorders with Ophthalmic and Thoracic Involvement

A variety of systemic conditions involve the thorax and the eyes. While subtle or nonspecific eye symptoms can be the initial clinical manifestation of some disorders, there can be additional manifestations in the thorax that lead to a specific diagnosis and affect patient outcomes. For instance, the initial clinical manifestation of Sjögren syndrome is dry eye or xerophthalmia; however, the presence of Sjögren lung disease represents a fourfold increase in mortality. Likewise, patients with acute sarcoidosis can initially present with pain and redness of the eye from uveitis in addition to fever and parotitis. Nearly 90% of patients with sarcoidosis have thoracic involvement, and the ophthalmologic symptoms can precede the thoracic symptoms by several years in some cases. Furthermore, a diagnosis made in one system can result in the screening of other organs as well as prompt genetic evaluation and examination of family members, such as in the setting of Marfan syndrome or Ehlers-Danlos syndrome. Multimodality imaging, particularly CT and MRI, plays a vital role in identification and characterization of these conditions. While it is helpful for ophthalmologists to be knowledgeable about these conditions and their associations so that they can order the pertinent radiologic studies, it is also important for radiologists to use the clues from ophthalmologic examination in addition to imaging findings to suggest a specific diagnosis. Systemic conditions with thoracic and ophthalmologic manifestations can be categorized as infectious, inflammatory, autoimmune, neoplastic, or hereditary in origin. The authors describe a spectrum of these conditions based on their underlying cause. ©RSNA, 2024.

Post-laser refractive surgery keratitis: A concise narrative review

Laser refractive surgery (LRS) is a specialized surgical discipline within ophthalmology that focuses on vision correction via laser techniques. LRS requires a high rate of accuracy and exactitude to improve the visual outcome and minimize complications, which may lead to delayed visual recovery. Keratitis, either infectious or noninfectious, is a post-LRS complication that requires early diagnosis and proper interventional measures. In this narrative review, we summarize different aspects of keratitis following LRS. This literature review aims to provide a thorough understanding of the causes of post-LRS infectious keratitis and its appropriate management for successful outcomes.

Nocardia infection following ocular surface surgery

OBJECTIVE

To investigate the clinical characteristics and treatment outcomes of Nocardia infection after ocular surface surgery.

METHODS

This is a retrospective study. Eight cases of culture-proven Nocardia infection, which developed within 1 month after ocular surface surgery were included. Demographics and clinical history of patients were investigated.

RESULTS

There were 8 eyes (2 left and 6 right) of 8 patients (5 males and 3 females), aged 27-65, with a median age of 52.9 years. Three cases underwent pterygium excision, three were subjected to conjunctival flap covering, and two were treated with lamellar corneal transplantation. The time interval between previous surgery and the onset of symptoms varied from 7 to 28 days (mean = 20.5 ± 7.13 days). All the cases presented grey-white infiltrates at the surgical incision site while appearing with six corneal ulcers and two conjunctival ulcers. Filaments of Nocardia were founded by confocal microscopy in two of the five cases. All responded poorly to medical therapy. Seven of the eight cases were treated with reoperation. Nocardia infection recurred in three cases after reoperation, and one was eviscerated.

CONCLUSIONS

Surgical trauma is a risk factor for ocular Nocardia infection. Nocardia infection should be suspected when secondary infection occurs in a surgical incision with an atypical clinical presentation. The use of corticosteroids may influence the efficacy of drugs. Complete removal of lesions may lower the recurrence of Nocardia infection with poor drug treatment effects.

Nocardia and Streptomyces keratitis in dogs: In vivo detection of filamentous bacteria by confocal microscopy

OBJECTIVE

To describe the clinical features of dogs with Nocardia and Streptomyces keratitis, including the results of in vivo confocal microscopy examinations.

ANIMAL STUDIED

A 15-year-old, male-castrated, miniature Schnauzer was presented with a multilobulated, cystic, pink, ulcerated corneal mass with surrounding dense leukocyte infiltrates. Cytologic evaluation of a corneal scraping identified pyogranulomatous inflammation and filamentous bacteria. Nocardia nova was cultured from corneal samples. Anterior lamellar keratectomy was performed to excise the affected corneal region and histopathologic evaluation confirmed the diagnosis of pyogranulomatous keratitis. A 10-year-old, male-castrated, Yorkshire terrier was presented for evaluation of a chronic anterior stromal corneal ulcer associated with a brown corneal plaque. Cytologic evaluation of a corneal scraping identified suppurative inflammation and filamentous bacteria. A Streptomyces sp. was cultured from corneal samples. The keratitis in both dogs resolved with therapy.

PROCEDURES

In vivo confocal microscopy examination of the corneal lesions in both dogs revealed dense accumulations of leukocytes and clusters of hyperreflective, slender, branching bacterial structures that were approximately 1.5-2.0 μm in diameter and 25-50 μm in length. Confocal microscopy imaging of the Nocardia isolate in vitro, and ex vivo canine corneas experimentally infected with the bacteria, was performed to corroborate the in vivo findings. The morphology of the filamentous bacteria was similar between the in vivo, in vitro, and ex vivo confocal microscopy examinations.

CONCLUSIONS AND CLINICAL RELEVANCE

Nocardia and Streptomyces spp. can be associated with infectious keratitis in dogs. In vivo detection of filamentous bacteria in the cornea can be accomplished by confocal microscopy.

Large mediastinal mass diagnosed as Nocardia infection by endobronchial ultrasound-guided transbronchial needle aspiration in a ceramic worker: A case report

Background

Nocardia is a ubiquitous soil saprophyte transmitted through airborne or direct cutaneous inoculation routes. Although Nocardia is more common in immunocompromised patients, Nocardia may also arise in apparently immunocompetent patients.

Case presentation

We report a rare case of Nocardia infection presenting as a large mediastinal mass in an immunocompetent ceramic worker. A 54-year-old man with no previous history of immune dysfunction, a ceramic worker by profession, was referred and admitted to our hospital because of a persistent fever for 19 days. Chest CT showed a large middle mediastinal mass. However, conventional anti-infective treatment was ineffective. Under the guidance of the Virtual bronchoscopic navigation (VBN) system, he underwent Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA). The purulent exudate obtained by EBUS-TBNA was further identified as Nocardia by weak acid-fast and metagenomic next-generation sequencing (mNGS). He was subsequently treated with intravenous imipenem/amikacin, switched to intravenous imipenem and oral trimethoprim/sulfamethoxazole, and the clinical symptoms were significantly improved.

Conclusions

Even in immunocompetent patients, Nocardiosis cannot be excluded. For the public, especially soil contact workers, precautions should be taken to avoid Nocardia infection from occupational exposure. This rare case may provide a diagnosis and treatment reference for clinicians.

A Case of Nocardia africana-Related Keratitis

Nocardia spp. are gram positive, aerobic, weakly acid-fast bacteria. Nocardia spp. keratitis is a rare ocular infection classically described following corneal injury or vegetative and soil exposure. However, keratitis caused by Nocardia africana had never been reported in the literature. We first reported a 70-year-old male who had a traumatic ocular injury to his left eye a month ago. With his complaint of left eye pain, reduced vision, and light sensitivity, the slit-lamp biomicroscopy showed the superficial multi-lobulated epithelial infiltration located at the inferior cornea with a positive fluorescein stain. Microscopic workup from corneal specimens demonstrated dry and chalky white colonies on blood agar and Lowenstein-Jensen media resembling Nocardia spp. The MALDI-TOF MS analyses using VITEK® MS exhibited N. africana. The corneal lesion was treated with 2% amikacin topical eye drops and responded well. The careful history-taking, precise clinical examinations, and meticulous microscopic assessment were the cornerstones of diagnosis. Definite diagnosis and timely treatment were essential to prevention of ocular morbidity in N. africana.

Infectious keratitis: A review

Globally, infectious keratitis is the fifth leading cause of blindness. The main predisposing factors include contact lens wear, ocular injury and ocular surface disease. Staphylococcus species, Pseudomonas aeruginosa, Fusarium species, Candida species and Acanthamoeba species are the most common causal organisms. Culture of corneal scrapes is the preferred initial test to identify the culprit organism. Polymerase chain reaction (PCR) tests and in vivo confocal microscopy can complement the diagnosis. Empiric therapy is typically commenced with fluoroquinolones, or fortified antibiotics for bacterial keratitis; topical natamycin for fungal keratitis; and polyhexamethylene biguanide or chlorhexidine for acanthamoeba keratitis. Herpes simplex keratitis is mainly diagnosed clinically; however, PCR can also be used to confirm the initial diagnosis and in atypical cases. Antivirals and topical corticosteroids are indicated depending on the corneal layer infected. Vision impairment, blindness and even loss of the eye can occur with a delay in diagnosis and inappropriate antimicrobial therapy.

Nocardia sienata: a new causative species of infectious keratitis

A 25-year-old man presented with a 2-month history of progressively worsening left eye pain and an atypical corneal ring infiltrate. His condition deteriorated despite topical antibiotic therapy. Cultures for bacteria, fungus and acanthamoeba, repeated twice, all demonstrated no growth. On third corneal scraping, culture on Middlebrook agar grew colonies after 3 weeks of incubation. Sixteen-second deep sequencing identified Nocardia sienata as the pathogen. This species of Nocardia has not previously been described as a causative pathogen for infectious keratitis. Sloughing and loose epithelium with recurrent filament formation are unusual in infectious keratitis and could be associated with this species. In culture-negative cases, clinicians should consider Nocardia as a cause of keratitis despite its rarity outside of south Asia and use steroids cautiously. Next generation sequencing technology may facilitate identification of the causate of keratitis and can be especially useful in culture-negative cases and with unexpected pathogens.

Amikacin potentiator activity of zinc complexed to a pyrithione derivative with enhanced solubility

Resistance to amikacin in Gram-negatives is usually mediated by the 6'-N-acetyltransferase type Ib [AAC(6')-Ib], which catalyzes the transfer of an acetyl group from acetyl CoA to the 6' position of the antibiotic molecule. A path to continue the effective use of amikacin against resistant infections is to combine it with inhibitors of the inactivating reaction. We have recently observed that addition of Zn²⁺ to in-vitro enzymatic reactions, obliterates acetylation of the acceptor antibiotic. Furthermore, when added to amikacin-containing culture medium in complex to ionophores such as pyrithione (ZnPT), it prevents the growth of resistant strains. An undesired property of ZnPT is its poor water-solubility, a problem that currently affects a large percentage of newly designed drugs. Water-solubility helps drugs to dissolve in body fluids and be transported to the target location. We tested a pyrithione derivative described previously (Magda et al. Cancer Res 68:5318–5325, 2008) that contains the amphoteric group di(ethyleneglycol)-methyl ether at position 5 (compound 5002), a modification that enhances the solubility. Compound 5002 in complex with zinc (Zn5002) was tested to assess growth inhibition of amikacin-resistant Acinetobacter baumannii and Klebsiella pneumoniae strains in the presence of the antibiotic. Zn5002 complexes in combination with amikacin at different concentrations completely inhibited growth of the tested strains. However, the concentrations needed to achieve growth inhibition were higher than those required to achieve the same results using ZnPT. Time-kill assays showed that the effect of the combination amikacin/Zn5002 was bactericidal. These results indicate that derivatives of pyrithione with enhanced water-solubility, a property that would make them drugs with better bioavailability and absorption, are a viable option for designing inhibitors of the resistance to amikacin mediated by AAC(6')-Ib, an enzyme commonly found in the clinics.

Applications of in vivo confocal microscopy in the management of infectious keratitis in veterinary ophthalmology

In vivo confocal microscopy (IVCM) is a relatively new ocular imaging technique that permits morphological and quantitative assessment of the living cornea on the cellular level. The applications for IVCM in clinical ophthalmology are numerous and diverse. There are several advantages inherent to IVCM over standard diagnostic techniques currently used to confirm a diagnosis of infectious keratitis in veterinary ophthalmology. With IVCM, images can be viewed in real-time providing immediate diagnostic information. Traumatic corneal sampling techniques are avoided, and the procedure can be repeated as frequently as is clinically indicated without risk of corneal tissue damage. Both superficial and deep corneal lesions can be evaluated by IVCM in an atraumatic fashion. Microorganism viability is not required for their detection and specialized diagnostic laboratory assay procedures are not necessary. Many larger infectious agents can be directly identified within corneal lesions by IVCM, including fungi and parasites such as Acanthamoeba spp. In other situations, such as bacterial infectious crystalline keratopathy, the biological systems associated with the microorganism can be detected within the cornea. The current resolution of IVCM is inadequate to directly visualize some corneal infectious agents, such as herpesviruses, but host responses and virus-infected epithelial cells can be identified. This review summarizes the current knowledge and applications of IVCM in the management of infectious keratitis in veterinary ophthalmology, including its use in animals with bacterial, fungal, parasitic, and viral keratitis.