Aeromonas Salmonicida as a Causative Agent for Postoperative Endophthalmitis.

We report a case of a 55-year-old female who presented with pain, redness, and profound visual loss in her right eye 2 weeks after cataract surgery. An ophthalmic examination showed light perception vision, corneal edema with severe anterior chamber reaction and hypopyon, exudative membranes on the anterior lens surface, and dense vitreous exudates. Under the impression of acute postoperative exogenous endophthalmitis, immediate pars plana vitrectomy with culture of vitreous aspirate and intravitreal antibiotic injections were performed. Bacterial growth was observed on culture plates and broths which were identified as Aeromonas salmonicida by VITEK 2 compact system. So far, no report has been published regarding endophthalmitis due to A. salmonicida. Here, we present the first report of A. salmonicida isolated from the ocular specimen.

Introduction

The genus Aeromonas consists of Gram-negative, rod-shaped, oxidase-positive, facultative anaerobic bacteria that are widely distributed in the aquatic environment. Previously, Aeromonas species were considered as pathogens in cold-blooded animals only, but gradually, they have been recognized as opportunistic pathogens for humans causing gastrointestinal infections and septicemia.[1] Rarely, they have been reported to cause ocular infections including corneal ulcers and endophthalmitis.[2] A list of infections caused by genus Aeromonas is mentioned in Table 1. There are a few case reports of endophthalmitis caused by Aeromonas species such as Aeromonas hydrophila and Aeromonas sobria in the literature.[34] Aeromonas salmonicida, a primary pathogen of fish, may cause furunculosis and other systemic infections in humans.[5] Ocular infections such as endophthalmitis have never been reported previously. To the best of our knowledge, this is the first report of endophthalmitis caused by A. salmonicida.

Table 1

Infections caused by genus Aeromonas in humans

Case Report

A 55-year-old woman underwent cataract surgery with intraocular lens (IOL) in her right eye (RE) elsewhere. The first postoperative period was uneventful, after which she complained of ocular pain, discharge, and gradual decrease of vision in the same eye for which she reported to our institute. Her best-corrected visual acuity (BCVA) in the RE was light perception. On slit lamp examination, the patient had conjunctival congestion, chemosis, marked corneal edema, grade 4 anterior chamber (AC) reaction with a hypopyon of 3 mm, and a thickened inflammatory fibrous membrane within the AC. There was no view of the fundus. No evidence of corneal, scleral, or orbital involvement was seen. Applanation tonometry reading was 19 mmHg and 12 mmHg in RE and left eye, respectively. The left eye had BCVA of 20/200 with immature cataract and normal fundus. B-scan ultrasonogram revealed dense membranous echoes in vitreous cavity suggesting endophthalmitis [Figure 1]. Aqueous humor and vitreous aspirate were inoculated in chocolate agar, blood agar (BA), thioglycolate broth, Sabaroud's dextrose agar, brain heart infusion broth (BHIB) and sent for Gram and KOH stain. Then, the patient underwent standard 20 g pars plana vitrectomy along with intravitreal injections of vancomycin (1 mg/0.1 ml), ceftazidime (2.25 mg/0.1 ml), and dexamethasone (400 μg/0.1 ml) at the end of the procedure. Direct mount showed Gram-negative rods on Gram's stain. Turbidity was found only in BHIB. Gram-staining from BHIB revealed Gram-negative rods. The subcultured colonies on BA were translucent simulating Pseudomonas aeruginosa. The next day, size of colonies became larger and color turned golden yellow and the isolate was identified as A. salmonicida by VITEK 2 (version 5.02) system (BioMerieux, USA). Antibiotic sensitivity was determined by Kirby-Bauer disc diffusion method, and the isolate was found to be sensitive for amikacin, gentamycin, and colistin. We repeated intravitreal antibiotics (amikacin [125 μg/0.1 ml][6] and dexamethasone) after 48 h and it responded well to the treatment. Six weeks after the surgery, her right eye BCVA was 20/400 with a quiet AC and posterior segment. There was a fibrous membrane anterior to the IOL obscuring the view of posterior segment (vitreous haze 2+). The patient was advised neodymium-doped yttrium aluminium garnet membranectomy for the same which she underwent without improving the visual acuity.

Figure 1

Right eye B-scan ultrasound imaging showing dense vitreous membranes

Discussion

Endophthalmitis is one of the most devastating diagnoses in ophthalmology. Approximately 90% of postoperative endophthalmitis cases develop after cataract surgery. According to the Endophthalmitis Vitrectomy Study, 94.2% of culture-positive endophthalmitis cases involved Gram-positive bacteria. Gram-negative species were isolated in only 5.9% of cases.[7] A. salmonicida, a Gram-negative bacilli belonging to the genus Aeromonas, was first discovered in a Bavarian brown trout hatchery by Emmerich and Weibel in 1894. Until recently, A. salmonicida was considered as a primary fish pathogen infecting cold-blooded vertebrates living at low temperatures (22°C–25°C) mainly salmonid fish hence named salmonicida.[5] It can also be found in the environment, diseased fish, and water and may be transmitted to humans by all these sources. In the present case, the possible route of infection could be eyewash with contaminated water after cataract surgery. Aeromonas species may cause gastrointestinal infections, furunculosis, and septicemia in humans,[1] but ocular infections such as corneal ulcers or endophthalmitis are very rarely reported. A. hydrophila has been reported to cause endophthalmitis after a penetrating injury, post-traumatic keratitis, contact lens-related keratitis, and endogenous endophthalmitis.[389] Lee et al. also reported a case of post-traumatic endophthalmitis in a fisherman caused by A. sobria.[4] However, A. salmonicida has been isolated from human blood samples in patients with furunculosis and septicemia, but it has never been identified in ocular specimens so far.[1] To date, no case of exogenous or endogenous endophthalmitis by A. salmonicida has been reported in the literature. This is the first reported case of culture-positive endophthalmitis caused by A. salmonicida. Initially, we presumed it to be a case of pseudomonas because of similar staining and culture characteristics, but later, it turned out to be a different organism on culture media which was identified as A. salmonicida by VITEK 2 system. In common with other endophthalmitis caused by Aeromonas, this case also showed a rapidly worsening course and a poor prognosis despite prompt diagnosis and management. Furthermore, the initial antibiotic injections possibly were not adequate therapy for this organism given the final sensitivity results, leading to subsequent poor visual outcome in this case.

Utmost microbiological vigilance is required to promptly identify this rare organism so that timely management of the condition is possible with appropriate antibiotics and surgery if required.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.