In VitroAntibiotic Susceptibility of Rapidly Growing Nontuberculous Mycobacteria Isolated from Patients with Microbial Keratitis

Ocular infections associated with atypical mycobacteria: A review

Atypical mycobacteria or non-tuberculous mycobacteria (NTM) are a group of acid-fast bacteria that are pathogenic to different parts of the eye. The organisms can cause a spectrum of ocular infections including keratitis, scleritis, uveitis, endophthalmitis and orbital cellulitis. Trauma, whether surgical or nonsurgical, has the highest correlation with development of this infection. Common surgeries after which these infections have been reported include laser in situ keratomileusis (LASIK) and scleral buckle surgery. The organism is noted to form biofilms with sequestration of the microbe at different inaccessible locations leading to high virulence. Collection of infective ocular material (corneal scraping/necrotic scleral tissue/abscess material/vitreous aspirate, etc.) and laboratory identification of the organism through microbiologic testing are vital for confirming presence of the infection and initiating treatment. In cluster infections, tracing the source of infection in the hospital setting via testing of different in-house samples is equally important to prevent further occurrences. Although the incidence of these infections is low, their presence can cause prolonged disease that may often be resistant to medical therapy alone. In this review, we describe the various types of NTM-ocular infections, their clinical presentation, laboratory diagnosis, management, and outcomes.

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.

Outcomes of Nontuberculous Mycobacterial Keratitis After Clear Corneal Incision Phacoemulsification Surgery: A Case Series of 6 Eyes in South Florida

PURPOSE

The purpose of this study was to present the successful management and outcomes in a series of 6 cases of culture-positive nontuberculous mycobacterial keratitis after clear corneal incision phacoemulsification surgery.

METHODS

This is a case series of 6 consecutive eyes that presented at the Cornea Division at an academic institution, diagnosed with culture-positive nontuberculous mycobacterial keratitis after phacoemulsification surgery.

RESULTS

Six eyes of 5 patients were included. The mean interval from cataract surgery to presentation was 7.7 weeks. All cases presented with intrastromal abscesses adjacent to corneal incisions, and 2 had scleral extension of the infection. Isolated organisms were Mycobacterium abscessus (n = 4), Mycobacterium chelonae (n = 1), and Mycobacterium mucogenicum (n = 1). All cases were treated with topical amikacin 8 mg/mL for 10.5 weeks on average. All cases received either oral clarithromycin at 500 mg twice-daily dosage or oral azithromycin at 500 mg daily. Two patients with scleral abscesses underwent surgical debridement with amniotic membrane grafts. All 6 eyes achieved infection resolution and good visual recovery, with the final visual acuity ranging from 20/20 to 20/60. None of the patients experienced recurrence of infection.

CONCLUSIONS

Prompt medical treatment with combined topical and oral therapy can lead to infection resolution and favorable visual recovery. Early surgical intervention can ensure good outcomes in cases of scleral extension.

Increase in infected corneal ulcerations in dogs during the northern Colorado's 2020 wildfire season

OBJECTIVE

In the fall of 2020, Colorado experienced the two largest wildfires in state history. The smoke blanketed the college town of Fort Collins, Colorado, the location of the Veterinary Teaching Hospital at Colorado State University (CSU-VTH). The objective for this cross-sectional observational study was to evaluate how these wildfires and the corresponding elevated air quality index (AQI)) was associated with infected corneal ulcerations in dogs when compared to the two previous years.

ANIMALS

Seventeen dogs were included in this study.

PROCEDURES

Medical records from dogs presented to the CSU-VTH ophthalmology service with infected corneal ulcerations in August, September, and October of 2020, 2019, and 2018 were evaluated. Only corneal ulcerations with growth on their microbial cultures were included in this study.

RESULTS

The study revealed a significant increase in prevalence of infected corneal ulcerations in dogs presented to the CSU-VTH during the three wildfire months of 2020 that is, 3.5% (9/255) when compared with the two previous years, 2019: 1.0% (4/383, p = 0.04), and 2018: 0.9% (4/457) (p = .01). The AQI (mean ± standard error) was also significantly elevated for dogs that presented with infected corneal ulcerations in 2020 (70.2 ± 5.8) compared with 2019 (19.7 ± 8.7) and 2018 (45.6 ± 8.7) (p < .01).

CONCLUSIONS AND CLINICAL RELEVANCE

Elevation of AQI from wildfires seems to be correlated with an increased prevalence of infected corneal ulceration in dogs. As the duration and frequency of wildfires continues to rise globally, the effects of these wildfires on animal health should be investigated further.

Antimicrobial susceptibility of rapidly growing mycobacteria using the rapid colorimetric method

Drug susceptibility testing (DST) of rapidly growing mycobacteria (RGM) are recommended for guiding the antimicrobial therapy. We have evaluated the use of resazurin in Mueller-Hinton medium (MHR) for MIC determination of RGM and compared the results with those obtained with the reference standard broth microdilution in Mueller-Hinton (MH) and with the resazurin microtiter assay (REMA) in 7H9 broth. The MIC of eight drugs: amikacin (AMI), cefoxitin (FOX), ciprofloxacin (CIP), clarithromycin (CLA), doxycycline (DOX), linezolid (LZD), moxifloxacin (MXF) and trimethoprim-sulfamethoxazole (TMP-SMX) were evaluated against 76 RGM (18 species) using three methods (MH, MHR, and REMA) in a 96-well plate format incubated at 37 °C over 3-5 days. Results obtained in the MH plates were interpreted by the appearance of turbidity at the bottom of the well before adding the resazurin. MHR and 7H9-REMA plates were read by visual observation for a change in color from blue to pink. The majority of results were obtained at day 5 for MH and 1 day after for MHR and 7H9-REMA. However, the preliminary experiment on time to positivity results using the reference strain showed that the resazurin can be added to the MH at day 2 to produce the results at day 3, but future studies with large sets of strains are required to confirm this suggestion. A high level of agreement (kappa 1.000-0.884) was obtained between the MH and the MHR. Comparison of results obtained with 7H9-REMA, on the other hand, revealed several discrepancies and a lower level of agreement (kappa 1.000-0.111). The majority of the strains were resistant to DOX and TMP-SMX, and the most active antimicrobials for RGM were AMI and FOX. In the present study, MHR represented an excellent alternative for MIC determination of RGM. The results could be read reliably, more easily, and more quickly than with the classical MH method.

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.

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.

Nontuberculous mycobacterial infection after clear corneal phacoemulsification cataract surgery: a report of 13 cases

PURPOSE

To review the patient profile, clinical presentation, management, and outcomes of nontuberculous mycobacterial (NTM) infection after clear corneal phacoemulsification.

METHODS

Review of consecutive cases diagnosed with NTM infection after phacoemulsification from 2004 to 2009. Demographic data, clinical characteristics, diagnosis, treatment, and outcomes were analyzed.

RESULTS

Thirteen eyes of 13 patients with mean age of 61.1 years, consisting of 7 men and 6 women were included. Twelve of 13 eyes (92%) underwent uncomplicated clear cornea phacoemulsification with posterior lens implant. Mean interval from surgery to onset of symptoms was 6.3 weeks, and time to referral ranged from 2 days to 9 months. Ten eyes (77%) presented with stromal wound abscess, whereas 3 (23%) appeared as iridocyclitis with posterior capsule plaques. Five eyes were clustered while the rest were isolated cases. All cases were culture positive for NTM. Two cases were treated medically, 3 had removal of lens implant and capsule, and 8 had penetrating keratoplasty with or without removal of lens implant, iridectomy, and/or pars plana vitrectomy. After a mean follow-up of almost 22 months, best-corrected visual acuity of 20/40 or better was achieved in half of the cases (54%). One case of recurrence was noted.

CONCLUSIONS

NTM infection should be suspected in patients presenting with corneal stromal wound abscess or iridocyclitis with posterior capsular plaques 6 to 7 weeks after phacoemulsification. Early diagnosis and treatment can lead to good outcomes, and management should include a combination of medical and surgical therapies.

Antibiotic resistance in ocular bacterial pathogens

Bacterial infections of the eye are common and ophthalmologists are spoilt for choice with a variety of antibiotics available in the market. Antibiotics can be administered in the eye by a number of routes; topical, subconjunctival, subtenon and intraocular. Apart from a gamut of eye drops available, ophthalmologists also have the option of preparing fortified eye drops from parenteral formulations, thereby, achieving high concentrations; often much above the minimum inhibitory concentration (MIC), of antibiotics in ocular tissues during therapy. Antibiotic resistance among ocular pathogens is increasing in parallel with the increase seen over the years in bacteria associated with systemic infections. Although it is believed that the rise in resistant ocular bacterial isolates is linked to the rise in resistant systemic pathogens, recent evidence has correlated the emergence of resistant bacteria in the eye to prior topical antibiotic therapy. One would like to believe that either of these contributes to the emergence of resistance to antibiotics among ocular pathogens. Until recently, ocular pathogens resistant to fluoroquinolones have been minimal but the pattern is currently alarming. The new 8-fluoroquinolone on the scene-besifloxacin, is developed exclusively for ophthalmic use and it is hoped that it will escape the selective pressure for resistance because of lack of systemic use. In addition to development of new antibacterial agents, the strategies to halt or control further development of resistant ocular pathogens should always include judicious use of antibiotics in the treatment of human, animal or plant diseases.

Fungal, Mycobacterial, and Nocardia infections and the eye: an update

Although relatively uncommon, fungi, atypical Mycobacteria, and Nocardia have been isolated from a variety of infections of eye including keratitis, scleritis, canaliculitis, dacryocystitis, endophthalmitis and orbital cellulites. The organisms typically cause a slowly progressive disease. The diseases caused by the organisms can pose both diagnostic and therapeutic challenges. In this manuscript we will describe updates on important aspects of the ocular infections caused by these organisms.

Phenotypic and molecular characterization of quinolone resistance in Mycobacterium abscessus subsp. bolletii recovered from postsurgical infections

Several outbreaks of infections caused by rapidly growing mycobacteria (RGM) were reported in many Brazilian states (2032 notified cases) from 2004 to 2010. Most of the confirmed cases were mainly associated with Mycobacterium massiliense (recently renamed as Mycobacterium abscessus subsp. bolletii) BRA100 clone, recovered from patients who had undergone invasive procedures in which medical instruments had not been properly sterilized and/or disinfected. Since quinolones have been an option for the treatment of general RGM infections and have been suggested for therapeutic schemes for these outbreaks, we evaluated the in vitro activities of all generations of quinolones for clinical and reference RGM by broth microdilution, and analysed the peptide sequences of the quinolone resistance determining regions (QRDRs) of GyrA and GyrB after DNA sequencing followed by amino acid translation. Fifty-four isolates of M. abscessus subsp. bolletii, including clone BRA100, recovered in different states of Brazil, and 19 reference strains of RGM species were characterized. All 54 M. abscessus subsp. bolletii isolates were resistant to all generations of quinolones and showed the same amino acids in the QRDRs, including the Ala-83 in GyrA, and Arg-447 and Asp-464 in GyrB, described as being responsible for an intrinsic low level of resistance to quinolones in mycobacteria. However, other RGM species showed distinct susceptibilities to this class of antimicrobials and patterns of mutations contrary to what has been traditionally defined, suggesting that other mechanisms of resistance, different from gyrA or gyrB mutations, may also be involved in resistance to high levels of quinolones.